1584_lnote_welding 2009.ppt

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Dr. N. RAMACHANDRAN, NITC 1




METAL JOINING

• Even the simplest object is an assembly ofcomponents

• Complex ones - greater number of parts-subassemblies joined to perform the function

• METHODS-

WELDING,

BRAZING,

SOLDERING,ADHESIVE BONDING,

MECHANICAL JOINING

NITC




WHY JOINING?

• IMPOSSIBLE TO MAKE AS ONE PIECE

• EASINESS AND ECONOMY INMANUFACTURE

• EASY IN REPAIRS AND MAINTENANCE

• FUNCTIONAL PROPERTIES DIFFER-

e.g.: Carbide tips of tools,corrosion resistant

parts, tungsten carbide tip of pens, brake shoes tometal backing etc…

• TRANSPORTING SITE/ CUSTOMER

NITC




CL SSIFIC TION

• According to the STATE of the materials

being joined

• Extent of external heating- PRESSURE• Use of FILLER materials

NITC




Joining Processes

RESISTANCE

MECH.

JOINING

ARCCUTTINGCHEMICAL

CONSUMABLE NON CONSUMABLE

Oxy-fuel

Thermit

LIQUID

SOLID

LIQUID-SOLID

Spot

Seam

Projection

Flash

Stud

percussion

GTAW

PAW

EBW

LBW

SMAWSAW

GMAW

FCAW

EGW

ESW

Forge

ColdUltrasonic

Friction

Explosion

Diffusion

Brazing

Soldering

AdhesiveBonding

Fastening

Crimping

Seaming

Stitching

NITC




H istory of welding

And

American Welding Society




Vulcan

The Roman

ire God




Welding Heat Exchanger




• Thermite Welding Patent 729573




• The Bible mentions Tubal Cain, " forged alltypes of tools from bronze and iron." Hemay have been the first to join metals withthe forging process. His flame was an openhearth into which he placed the metals to be

heated to the forging temperature.• In 1892 Morehead and Wilson accidentallydiscovered how to make acetylene. It wasfound that combining acetylene withoxygen produced the hottest flametemperature--5720 degrees F. Since this iswell above the melting point of most metalsthe oxyacetylene welding process soondeveloped.

HISTORY OF WELDING




HISTORY OF WELDING3000 B.C.

• It was around this time that the Sumerians joinedmetals together in a “hard soldering” process to createswords for battle.

• In the tomb of Queen Pu-abi, several gold artifacts buried with her show signs of being brazed.

• Also around this time, the Egyptian culture usedcharcoal fires to turn iron ore into sponge iron.

• This was then beaten to weld the particles together,creating some of the first accounts of “pressurewelding” (Sapp 2003)




• 1000 B.C.

• The first forge welding came along around 1000

B.C. (Sapp 2003). This process involves heating themetals and then using pressure to bond the piecestogether (Fogg 1997). An archeological dig found ironand bronze artifacts that had been forge welded anddated from this time.

• Four boxes made of gold were also found around thistime in Ireland. These boxes showed evidence of being

pressure welded on some of the joints. This was donethrough a hammering process that fused the piecestogether (Sapp 2003).




• 60 A.D.

• Around 60 A.D., an author named Pliny wrote

about some of the information that he knew aboutwelding. He wrote about the brazing process for goldat this time and talked of the salts that were used for aflux mixture (Sapp 2003). Brazing is defined as, “a

process intended to permanently join two or more

metals/materials together to form a single assembly by heating them in the presence of a filler metal that begins to melt above 450° C (840° F)” (Kay2003). Flux is a material used to melt and keep themetal from oxidizing (Fogg 1997). Pliny also goes

on to describe a way to determine how easily a metalwill braze by looking at the metals color after itoxidizes (Sapp 2003).




• 400 A.D.

• The Iron Pillar in Delhi, India, is a monument to

welding technology itself. Created around 400 A.D.and weighing around six tons, this giant column is

around 25 feet tall and 16 inches in diameter at the

base. Formed from iron billets, this column was

fused together by forge welds. This pillar is even

more impressive when one realizes that the iron

obtained for use at this time was harvested from

meteors, and only in small quantities (Sapp 2003)




• 1776

• A scientist named Antoine Lavoisierdiscovered in 1776 that if an atmosphere

were made entirely of oxygen, a metal

could be burnt in that environment. This

experiment with oxygen lead to a belief that

oxygen could be used to cut metals. This

left over metal oxide could also be melted at

lower temperatures, showing a change inthe state of the metal (Sapp 2003).

1801




• 1801

Sir Humphrey Davy was also a leadingscientist in the production of modernwelding practices. In 1802, Sir Humphrey

created the first human created electricarc. He used high voltage electricity and a

pair of carbon rods and produced a changein one that jumped to the other. This is nowthe basis for what is now known as arc

welding (Hoyle 2003).• 1846

• A British scientist named James Nasmyth develops a uniform convex curveto the sides of metal pieces to be

welded. By doing this, the adhesion between the two metals starts at the middleand works its way out. This helps inexpelling the flux and other impurities outof the joint, instead of trapping them inwhich makes the joint weaker (Nasmyth

1997).

Sir Humphrey Davy Bachman, Michal. (2003).

Davy, sir humphery.Retrieved December 1, 2003

fromhttp://www.jergym.hiedu.cz/~bachmanm/images/davy.jpg

http://www.jergym.hiedu.cz/~bachmanm/images/davy.jpg








• 1800-1850s• Scientists are using the oxy-hydrogen blowpipe as a laboratory tool

to examine refractory metals to the extreme temperature of 4468°F.• 1800• Alessandra Volta discovers that two dissimilar metals connected by

a substance became a conductor when moistened, forming a'Voltaic Cell'.

• 1801• Sir Humphrey Davy (1778-1829) of London England, experimented

and demonstrated the arc between two carbon electrodes using abattery. This was the forerunner to electric-arc lighting.

• Vanadium was discovered in Mexico and was thought to be a formof chromium for the next three decades. In 1830, it wasrediscovered by N.C. Sefstrom, and in 1887, H.E. Rosco isolatedthe element from its compounds, mainly vanadite and carnotite. Itwas named for the Scandinavian love goddess Vanadis.

• 1808• Magnesium is discovered as a chemical element by Sir Humphrey

Davy.• Sir Humphrey Davy proved the existence of aluminum.




• 1818• Robert Hare, a professor of Chemistry at the University of

Pennsylvania invents the hydrogen blowpipe.• 1820• Hans Christian Oersted established connection between electricity

and magnetism.• Andre-Marie Ampere pioneered the field of electromagnetism.• 1823• Charles Macintosh opens a rubber factory in Glasgow Scotland.

• 1827• Friedrich Wholer discovers aluminum in 1827• 1828• Wallaston produced sponge platinum and welded it together by

cold-pressing, sintering and then hammering while the metal washot.

• 1831• Michael Faraday invents the Dynamo creating electricity from

magnets




• 1835-1836• English chemist Edmund Davy (1785-1857), a cousin of Sir Humphrey Davy described the

properties of acetylene, but was unable to give correct formula.• Frenchman Sainte Claire Deville invents the oxygen-hydrogen blowpipe. Used mainly as

laboratory equipment for melting platinum and producing enamel.

• 1838• Charles Goodyear discovers the vulcanization of rubber, giving rise to the development ofrubber hoses for welding gases.

• Eugene Desbassayrs de Richemont patents a process of fusion welding• 1839• Michael Faraday discovers the homopolar device that generates voltage.• 1840

• Frenchman E. Desbassayns de Richemont invents the first air-hydrogen blowpipe.• de Richemont coins the phrase "soudure autogène", improperly translated into English as

"autogenous welding". Welding implies solid state whereas fusion welding implies a liquidstate.

• 1841• German H. Rossier used the air-hydrogen blowpipe for soldering lead.• 1846

• James Nasmyth, while investigating the proving of ship chain for the British Admiralty,discovered and gave the reason for the convex forge welding "scarf". By preparing thesurfaces to be welded with a slightly convex surface the flux and swarf are squeezed outof the joint. Otherwise they are trapped in the joint weakening it. This was the firstimprovement in the forge welding process in 3000 years. Prior to this time the shape of the

joint was randomly flat concave or convex.




• 1856 • James Joule begins to experiment with a relatively new form of power

called electricity. Through his experiments, James develops the first arcwelding techniques in history (Roberge 2003).

• 1860s• An Englishman named Wilde successfully used the theories of Volta and Davyand the primitive electric sources of the time to make "Joins" and received apatent for the earliest form of the art now known as "electric welding".

• 1860• French chemist Berthelot (1827-1907) accurately gave the correct formula of

C2H2 to acetylene. Also found it to be unstable (1863) under certain pressure

and temperature.• 1862• A German, Friedrich Wohler (Woehler), produces acetylene gas from calcium

carbide.• 1863• The first successful oil pipeline was built by Samuel Van Sickel at Titusville,

Pennsylvania where 2-1/2 miles of 2 inch diameter cast Pipeline was laid forthe transfer of 800 barrels of crude oil. The pipe was screw coupled andhammered since welding was not yet invented for pipe joining. The Dressercoupling, invented in 1891 was the first time a mechanical joint could beassembled without excessive leaking. This method was the standard forpipelining until the mid-1930s, when welding overtook the assembly process.




• 1865• John Motley Morehead, a graduate of North Carolina State

University in 1891, was working as a chemist for Willson AluminumCompany determined that when heating slacked lime mixed withcoal tar and immersed in water would produce acetylene gas.

Acetylene is formed when bicarburet of H2 and ground carbonproduces a solid of calcium carbide when immersed in water. Thiswas originally discovered 56 years earlier by Edmund Davy.

• 1876• Otto Bernz of Newark New Jersey founded the Otto Bernz Company

selling plumber's tools and the gasoline torch "Alway's Reliable".

• 1877-1903• Development of gas welding and cutting, carbon arc and metal arc

welding.• Elihu Thomson invents a low-pressure resistance welding machine

which was accomplished by causing internal resistance enough toreach the plastic stage of a metal. Later, it was referred to as

Incandescent Welding.• 1877• During a lecture at the Franklin Institute (Philia), E. Thomson

reversed the process of (...)




• 1881

• A man named Augusta De Meritens used a form of arcwelding to adhere two lead plates together to made a

battery. He worked along with another man named NikolaiN. Bendaros, who would later gain the patent for thiswelding process. Known as carbon arc welding, Bendarosand another Russian scientist, Stanislaus Olszewski, wouldobtain patents for this variation of arc welding in various

countries, including America and Britain in the next fewyears. This type of welding would gain in popularity at theend of the 19th century and into the first years of the 20thcentury (Cary pg. 9).

• 1886

• Bendaros receives a patent from Russia for a form ofcarbon arc welding that actually could cut metal. Theprocess was named "Electrohefest" after the Greek god ofFire and Blacksmithing, Hephaestus (Sapp 2003).

• 1881

http://www.bsu.edu/web/cwjohnson2/welding.html

http://www.bsu.edu/web/cwjohnson2/welding.html




1881

• Auguste DeMeritens working at an associated laboratory founded by theperiodical "l'Electricien" - Cabot Laboratory (Cabat), France was using arc heat to join lead plates for storage battery. French Patent Number 146010 was issued.

• 1885• Nikolai N. Benardos (Bernados) and Stanislav Olszewaski (Olszewaski) secured a

British patent with carbon arc welding. Both men were working under the directionof A. DeMeritens with the arc lighting industry at the Cabot Laboratory (Cabat) inFrance. Carbon was oxidized at the carbon tip and created CO2 at the arc forshielding. Both men had to generate their electricity using a steam-engine (prime-mover) to turn the generator and produce electricity. The alternative was to usebatteries which did not last long because of the short-circuiting involved. Patentsapplied for and received besides Britain: Belgium, Germany, Sweden, andFrance.

• 1886• N. N. Benardos obtained Russian Patent (No. 11982) electric arc welding with

carbon electrode called ""Elecktrogefest" or "Electrohephaestus". The methods ofcutting and welding metals by the arc was termed "Electrohefest" in memory(sic)of Hephaestus, the ancient Greek god of Fire and Blacksmith work. (The Romansrenamed Hephaestus to Vulcan and which is shown on the title page, giving

instruction to the craftsmen forging metal.)• Benardos receives permission from the Russian Government to organizeproduction in 1885 for "The production of this plant is based on welding andbrazing by electricity and also producing devices for electrical illumination"(Note: emphasis mine)

• Electric furnace installed for production of aluminum alloys. An important step inearly development of the Aluminum industry.




• 1887• N.N. Benardos and S. Olszewaski secured an American Patent for

the welding apparatus. (U.S. Patent No. 363320, May 17)• The "blowpipe" or "torch", using the gases acetylene and liquefied

air or oxygen, was developed.• Thomas Fletcher develops blowpipe that could be used with eitherhydrogen or coal gas and oxygen

• An English shop began making tanks, casks, and iron gardenfurniture with the electric arc process.

• 1888

• Benardos/Olczewski granted patent 12984 for Carbon Arc Welding.• 1889• Hans Zerner is issued German Patent 53502.3.12.1889 for the Twin

Carbon Arc welding process?.• C. Coffin is issued patent 395878, 'Process of Electric Welding'.• The US Commissioner to the 1889 Paris Universal Exposition upon

seeing the arc welding process demonstrated wrote in a report "...Asthe metal is burnt and brittle where it is welded, the process is not asuccess."




• 1890 • C.L. Coffin discovers a method of transferring metal from a metal electrode to

the joint to fill the gap in the joint. For his work, Coffin was able to patent his idea,which was the first to use a metal electrode (Cary pg. 9).

• C. L. Coffin in Detroit Michigan awarded first U.S. Patent (No. 419032, Jan 1) formetal electrodes. This was the first record of metal melted from an electrode andactually carried across the arc to deposit filler metal in the joint to make the weld. Oneelectrode was carbon and the other electrode was filler material.

• Coffin also described the GTAW beginnings when a weld was made in non-oxidizingatmospheres.

• A bank robber in Great Britain used the newly developed "blowtorch" to gain accessto bank vaults.

• 1892

• Canadien Thomas 'Carbide' Willson and American James Turner Moorhead begin tocommercially produce acetylene as a product from calcium carbide in Spray, NorthCarolina.

• Slavianoff suggests that a bare metallic electrode could be substituted for the carbonelectrodes of the Benardos process.

• Concurrently, C. L. Coffin is also credited with introducing the bare metallic electrodein the US

• Baldwin Locomotive Works was using Carbon Arc Welding (CAW) for locomotivemaintenance. The weld joints were hard and brittle because of the carbon flaking offinto the weld puddle.

• 1886-1898• Elihu Thompson of the Thompson Welding Co. invented Resistance Welding (RW).




• 1895

• The combustion of Oxygen and Acetylene wasdiscovered by Henri LeChatelier in his home country of

France. Describes combustion of acetylene with equalvolume of oxygen proceeds in two stages:

• Step 1: 4 CO + 2O2 = 4CO2

• Step 2: 2 H2 + O2 = 2H2O• Machine for liquid air generation placed in operation

• Lord Reyleigh and Sir William Ramsey discover Argon(Ar).

• Konrad Roentgen (Bavaria) observed the effects of x-radiation while passing electric current through a vacuumtube.




• 1895-1905• During a 10 year period in the U.S. and at a rate of one

accident per day, boilers were exploding with the loss of

life from the accidents at twice that rate.• 1900• E. Fouch and F. Picard develops oxyacetylene torch in

France.• 1901

• Menne invented the Oxygen Lance in Germany.• Soon after Charles Picards invention of the oxyacetylene

blowpipe in Paris France, this invention was called uponto repair a cast iron part on an acetylene pump. Quite byaccident, the filler metal had enough silicon present to

prevent the formation of the excessively hard white iron.• 1902• President Teddy Roosevelt took over the Panama Canal

project from the French.

1903




• 1903• Hans Goldschmidt of Essen, Germany invented Thermit Welding (TW), an

exothermic reaction between aluminum powder and a metal oxide.. Used to weldrailroad rails together.

• Oxyacetylene is applied commercially.• 1904

• Concentrated Acetylene Company invents the portable cylinder for the autoheadlights.• 1905• L. W. Chubb of Westinghouse Electric & Manufacturing, East Pittsburg, PA,

experiments with electrolytic condensers and rectifiers and found that wires could beconnected to aluminum plates. Also found that copper could be joined in a likemanner. When the cells discharged, sparks were formed.

• 1907• Two German welders came to the U.S. and formed Siemund-Wienzell ElectricWelding Co. and patented a metal arc welding method. Another German formedcompany, Enderlein Electric Welding Co. also started up. This was the beginning ofthe arc welding industry in the U.S.

• Lincoln Electric Company of Cleveland Ohio began by manufacturing electric motorsin 1895. By 1907, Lincoln Electric were manufacturing the first variable voltage DCwelding machine.

• 1907-1914• Oscar Kjellberg (pronounced 'Shellberg') of Sweden and the ESAB (Elektriska

Svetsnings-AtkieBolaget) Company invented the covered or coated electrode bydipping bare iron wire in thick mixtures of carbonates and silicates. The purpose ofthe coating was to protect the molten metal from oxygen and nitrogen. His pioneeringof covered electrode development paved the road during the next twenty years in theresearch of reliable flux coated electrodes.




• 1908• Oscar Kjellberg received Patent No. 231733 for the coated welding

electrode.• N. N. Benardos develops electroslag welding process.• 1909• Strohmenger developed the Quasi-arc electrode which was wrapped in

asbestos yarn.• The keel of the H.M.S. TITANIC was laid on March 31 at Harland and

Wolff shipyard.

• Schonner, a physicist with BASF (Badischen Anilen und SodaFabrik)invents the plasma arc system using a gas vortex stabilized arc.

• First industrial application of plasma at BASF (Badische Anilin undSodafabrik) by a physicist manufacturing nitrogen dioxide (NO2).• 1910• Charles Hyde of Great Britain is issued a patent for brazing steel tubes. By

clamping two pieces into position, copper is placed in the joints as metallicstrips, plating or powder mixed in a paste. Heated in a hydrogen furnace(oxygen-free atmosphere) and by capillary attraction flows copper into the

joint• 1911• H.M.S. TITANIC is launched on May 31. • First attempt to lay 11 miles of pipeline using oxy-acetylene welding near

Philadelphia, Pennsylvania.• American physicist (Matters) developed a plasma arc torch for heating a

metal fusing furnace.




• 1912• Lincoln Electric Co. introduced the first welding machines after

experimentation started in 1907.• E. G. Budd Spot Welds (SW) the first automobile body in Philadelphia,

Pennsylvania.• Langmuir gives the "plasma" to a gas or gas mixture brought to such ahigh temperature that all diatomic molecules are dissociated and theatoms partially ionized and where all monotomic gases are fully ionized.

• Firecracker welding technique, a version of shielded metal arc welding ispatented in Germany.

• Strohmenger introduced coated metal electrodes in Great Britain. Theelectrodes had a thin wash coating of lime or clay resulting in a stablearc.

• Strohmenger obtained US patent covering an electrode coated with ablue asbestos with a binder of Sodium Silicate (NAXX). This was the firstelectrode which produced weld metal free of impurities.

• 1913• Avery and Fisher develop the acetylene cylinder in Indianapolis, Indiana.• 1914• A 34 mile pipeline was laid near Enid, Oklahoma using oxy-aceylene

welding for the oil industry.




• 1915-1916• Underwater cutting was carried out but interest did not come about until 1926.• 1916• Companies licensed resistance welding equipment, mostly spot welding was the

intended use.

• 1917• Because of a gas shortage in England during World War I, the use electric arc

welding to manufacture bombs, mines, and torpedoes became the primaryfabrication method.

• 1918• Admiralty testing of metal-arc welding on Barge Ac 1320 leads Lloyd's Register to

permit metal-arc welding in main structures on an experimental basis.• 1917-1920• During World War I, a Dutchman, Anthony Fokker, began using welding in the

production of Fuselages in German fighter planes.• HMS Fulagar (Fullagar) was first all welded hull vessel - Great Britain.• The repair of sabotaged German ships in New York Harbor highlighted the first

important use welding because the German merchant marines tried to destroythe ships boilers on 109 ships. A team of engineers from a railroad company(possibly the Rock Island Line) was tasked to the repair. Later, 500,000 troopswere delivered to the European War in France using these repaired ships. Thesuccess of the weld repairs catapulted welding to the arena for manufacturingand repair and dashed it sordid past as a controversial operation.




• 1919• President Woodrow Wilson established The United States Wartime Welding

Committee of the Emergency Fleet Corporation under the leadership of Dr. Comfort Avery Adams.

• Dr. Comfort Avery Adams, held a meeting on January 3rd to form the "AmericanWelding Society ". The Constitution of this meeting was approved on March 27.

• C. J. Holslag used Alternating Current (AC) for welding, but this was not popular until1930.

• The AWS Constitution of the January meeting was approved on March 27.• Reuben Smith developed and patented the paper-coated electrode. The weld did not

leave a slag and produced an acceptable weld.• 1920s• Various welding electrodes were developed:

– Mild steels electrodes for welding steels of less than 0.20% carbon; – Higher carbon and alloy electrodes; and

– Copper alloy rods.

• Researchers found that Oxygen (O2) and Nitrogen (N2) when in contact with moltenmetal caused brittle and porous welds.

• Alexandre and Langmuir, from General Electric Co., used Hydrogen in chambers toweld. Began with two carbon electrodes and later switched to Tungsten.

• Bundy-Weld of Bundy Company, Detroit Michigan uses sheetmetal coated with acopper paste and is rolled tightly around itself and placed in a furnace. The brazed joint is formed into one piece tubing.

• The automotive industry began using Automatic Welding with a bare wire fed to theworkpiece to the production of differential housings.

• Poughkeepsie Socony (1235 tons), the first all-welded tanker was launched in theUSA.

1920




• 1920• P.O. Nobel of General Electric Company developed automatic welding,

using Direct Current (DC) using the arc voltage to regulate feed rate.Primary use was to repair worn motor shafts and crane wheels.

• The British ship "Fulagar" was constructed by the Cammell-Lairds and

launched. In 1924, the ship grounded. A report in the British "Journal ofCommerce" (July 17, 1924) reported that she held steadfast and if rivetswere used in the construction, the ship would surely have opened up andnot be able to get off the bank.

• After WW I, the Treaty of Versailles limited the Germans from designing andbuilding ships in excess of 10, 000 tons for armored ships and cruisers notto exceed 6,000 tons. Welding was an experimental production option

before WW I but the Germans used it to develop the next stage of warshipsby saving weight whereby the ship could then carry more armament orarmor plating in selected areas.

• Torch brazing is in full swing using silver and gold filler metals and mineralfluxes as protective cover.

• Electrification of Russia begins utilizing hydroelectric power sources.• 1921

• Leslie Hancock pioneered flame cutting machine where the burner followedthe path of a magnetized stylus tracking around the contour of a metaltemplate. The stylus is propelled by a gramophone motor.

1922




• 1922• "No longer in the tones of a Walt Whitmanesque muscular America, the

skyscraper celebrated the technology that was bringing the world together."• The first issue of the "Proceedings of the American Welding Society" was

published in January (Vol. 1, No. 1). The name was changed in February,

the next month, to "Journal of American Welding Society ".• The Prairie Pipeline Company weld an 8 inch diameter pipeline 140 mileslong to carry crude oil from Mexico to Jacksboro, Texas. The advantage ofwelding over fittings saved the project 35 percent and the cost of weld, laborand material was $2.00 per welded joint.

• 1923• Institute of Welding Engineers was formed and headquartered in New York

City.• Naval Research Laboratory (NRL) was formed by the US Government

which was motivated by Thomas Edison's belief that history demonstrates arelationship between technological innovation and national security.

• 1924• 1st all-welded steel buildings constructed in U.S. by General Boiler Co. "to

the exclusion of rivets".• Resistance, gas and metallic arc welding in the manufacturing of all steel

automobile bodies at the E.G. Budd Manufacturing Company.• Mechanical flash welder used for joining rails together.• First recognition of welding design was presented in papers written by: J. C.

Lincoln, S. W. Miller, C. J. Holslag, H. A. Woofter, and J. H. Deppler.

1925




• 1925• ASME Boiler Code Construction Code Section VIII is issued for unfired pressure

vessels.• AWS Board of Directors approves "Standardization of Hose Connections for Welding,

and Cutting Torches and Regulators"• AWS held First Welding Show with the National Fall Meeting, 21-23 October, in Boston.

• A.O. Smith fabricates a single-piece heavy walled pressure vessel entirely by weldingand was PUBLICLY tested then placed in an oil cracking service.

• 1926• H.M. Hobart and P.K. Devers used atmospheres of Helium and Argon for welding with a

bare rod inside the atmosphere. Due to the impurities of the inert gases and thecorresponding high cost along with a lack of knowledge about current density,commercial applications were not realized at this time.

• UNA-METHOD - Trade name for the rail joint welding process, arc welding apparatus,electrodes and supplies. UNA Welding & Bonding Co. Cleveland Ohio.• FUSARC - (need info)...?• Irving Langmuir, a noted chemist with General Electric Co. developed the Atomic

Hydrogen Welding (AHW) Process. Co-authored with R. A. Weinman the paper was"Atomic Hydrogen Arc Welding"

• Naval Research Laboratory (NRL) employee, P. W. Swain authored a paper "X-raytests of weld " which was to have an impact with the welding industry much longer thanthe introduction of Atomic Hydrogen Arc Welding. The technique used a gamma-rayradiation as a shadow method to detect flaws in cast or welded steels. The techniqueswas used to detect flaws on the US Navy 9000 tonne heavy cruisers. The process waslater identified as a Nondestructive test method and contributed to the success ofdeveloping improved steel castings for the U.S. Navy.

• Landstroth and Wunder of A. O. Smith Co. solid extruded heavy coatings for metal-arcwelding electrodes.




• 1927• Lindberg's Ryan monoplane fuselage was manufactured with welded steel

alloy tubing.• Soviet Union production of Resistance Welding machines at Elektrik Works

called the "AT-8" and the "ATN-8: apparatus's for spot-welding and the"AS-1" and the "AS-25-1" for buttwelding.• John J. Chyle of A. O. Smith Corp. invented and patented the first

extruded, all-position, cellulosic, titanium dioxide later classified as E6010type welding electrode.

• 1928

• In East Pittsburgh, Pennsylvania, on the Turtle Creek, America's First All-Welded Railroad Bridge was erected by Westinghouse Electric andManufacturing Company. Westinghouse used the bridge to transport thelarge generators from facilities to the rest of the country by way of therailways. Weighing in at 20,000 pounds and at 62 foot long, the bridge wasmanufactured without the use of rivets, a common method of bridgeconstruction of those days. The testing of the bridge was completed by

driving a locomotive on the bridge. (Information Courtesy of Mr. LaFave)• Code for Fusion Welding and Gas Cutting in Building Construction

(predecessor of AWS D1.1) was issued by the American Welding Society.




• 1929• Lincoln Electric Co. started production of heavy coated electrodes

(Fleetweld 5) and sold the electrodes to the public. Sues A.O. Smithand wins.

• 1st European All-Welded bridge in Lowicza, Poland. Designed in1927 by Professor Stefana Bryly and spanning the Sludwie Riverthis bridge was still in use as late as 1977, whereby it was beingreplaced with a newer highway and bridge which is designed forwider traffic. The Polish Government planned to move the bridge 80meters up stream and establish the bridge as a historical monument.In 1995, AWS President ED Bohnart presented to the Governmentof Poland, the AWS Historic Welded Structure Award.

• Welding symbols are established by the American WeldingSociety

• General Electric experiments with "Controlled-Atmosphere brazing",using hydrogen gas for copper to steel brazes.

• Welding conferences are held on the campuses of Lehigh andSyracuse

1930 1940




• 1930-1940s• Atomic hydrogen arc welding process developed. Found that hydrogen

was liberated releasing heat, which was 1/2 of the BTU of acetylene.Used primarily for tools steels. Development included an automaticversion of the process.

• 1930• Specifications for welding electrodes were beginning to be written.• H. M. Hobart issued Patent Number 1746081, for "Arc Welding" and P.

K. Devers was issued Patent Number 1746191 for "Arc Welding" on Feb4 for using a concentric nozzle with a wire feed. This became known lateras Gas Metal Arc Welding (GMAW). Work was based on various

atmospheres in 1926.• Germany started development work to find a suitable substitute for their

dwindling supply of critical alloys. Experiments in the U.S. and Germanyfound that Thermoplastics when heated could be pressed together andobtain a permanent bond. In 1938 this principle was incorporated into"Hot Gas" welding technique. Thermoplastic rod and sheet were heated

simultaneously by a stream of hot air while the rod was pressed into thesheet causing a bond. World War II forced Germany to further developand use welded Thermoplastic as a corrosion resistant structuralmaterial.




• 1930 continued…. • Stud Welding (SW) was developed by the New

York Navy Yard to fasten wood to steel.• Submerged arc welding developed by National

Tube Co. in McKeesport, PA by Robinoff. Latersold rights to Linde Air Products and renamedUNION-MELT. Used in late 30s and early 40s in

shipyards and ordnance factories.• 1st all-welded merchant ship was built in

Charleston, South Carolina.• Advancements in protective atmospheres that

dissociate chromium oxide from the surface ofstainless steel are performed in furnaces withoutthe mineral flux and were found in laboratorieswith no commercial equivalence

• 1931




• 1931• E. G. Budd Manufacturing Company of Philadelphia spot welded stainless steel

(18-8) and built the Privateer. The spot-welding was a process called"shotwelding" a proprietary process developed by E.G. Budd.

• Combustion Engineering shipped the first commercial land boiler fabricated by

ASME welding code to Fisher Body Div. of General Motors Corporation.• 1932• Submerged Arc Welding (SAW) developed by National Tube Co. in McKeesport,

PA by Robinoff. Later sold rights to Linde Air Products and renamed UNION-MELT. Used in late 30s and early 40s in shipyards and ordnance factories.

• British Corporation Register and Lloyd's introduce revised rules and approvals forthe use of welding on ships.

• 1933• Lincoln Electric Co. published 1st edition of "Procedure Handbook of Arc Welding

Design and Fabrication" with the purpose to have its customers use arc weldingefficiently. As a full service company, this book provided the customers aknowledge of welding education and training.

• English Antiquarian, H. A. P. Littledale patents the "Littledale Process (BritishPatent No. 415,181)", following the same approach that Pliny and Theophiluswrote about from the past two millenniums. Mixing copper salts with seccotineglue ultimately would produce the following reaction {CuO+C -> Cu + CO} which iswhere brazing would theoretically be reached. The temperature the reaction takesplace: 850C.




• A major innovation wasdescribed in a patent (USPatent number 2,043,960)

that defines the Submerged Arc Process invented byJones, Kennedy andRothermund. This patentwas filed in October

1935 and assigned to UnionCarbide Corporation. TheSpecification states, Page 4,Column 2, Lines 4 through 7that the application was in

part a continuation ofapplications Serial Numbers657,836 and 705,893 filed inFebruary 1933 and January1934.

1934

http://www.netwelding.com/History_Submerged_Arc%202.htm







• 1934• 1st All-welded Excavator - HARNISCHFAGER Corp.• 1st All-welded British bridge - Middlesborough, England

• Lloyd's Rules for pressure vessels permits inspectionusing X-Ray technology. In Scotland, welding wasbeginning to be recognized as a separate crafts trade andthe Trade Unions were opposed to this recognition. TheGeneral Secretary of the Boilermaker's Union argued thatit was unfair to condemn any young man to a lifetime of

welding. (Scotland). The Shipbuilding Employers insistedon the separate recognition.

• Westinghouse introduces the "Ignitron" which wouldbecome the basis for resistance welding timing controllers.

• American Welding Society presents John C. Lincoln the

Samuel Wylie Miller Medal for "Meritorious Achievement".The award cited him for his work on the variable voltagemachine, the ductility and strength of welds, the carbonarc automation process, and his efforts to expand the useof welding in many industries.

• 1935




• 1935• Granulated flux developed in 1932 and a continuous bare wire feed became

known as "Submerged Arc Welding (SAW)" and saw major applications inshipbuilding and pipe fabrication (see 1932 for a different account).

• Solid extruded electrodes are introduce in Britain and subsequently the first

British welding electrode standard written.• Welding has "Arrived" when London, England hosts 900 attendees at the "GreatSymposium" on the "Welding of Iron and Steel"

• Solar Aircraft Company of San Diego California develops a flux to combatwelding problems with stainless steel manifolds for the U.S. Navy and wasregarded as a closely-guarded military secret. Where flux is applied to the frontof the weld, this was placed on the backside of weld, protecting from oxide

formation. Later, the product was developed further to accommodate the Heliarcprocess.• 1936• 1st All-welded Box Girder Crane by HARNISCHFAGER Corp., Milwaukee WI.• 1st All-welded Gear were fabricated by HARNISCHFAGER Corp. Milwaukee WI.• First Specification for Design, Construction, Alteration and Repair of Highway

and Railway Bridges by Fusion Welding was issued by the American WeldingSociety.

• Tentative Rules for the Qualification of Welding Processes and Testing ofWelding Operators was submitted by AWS.

• The Soviet Union at the Electrik Works started using the electronic control gearsas the first valve timer with a thyristor contactor (RVE-1) for resistance welding.

• Japan Welding Society stipulates the rules of qualification testing in "The

Standard of Qualification for Arc Welding Operator".

1937




• 1937• BS 538: Metal arc welding in mild steel, was issued, legitimizing arc

welding structural applications.• Norman Cole and Walter Edmonds, metallurgists from California are

granted a patent for their product named "Colmonoy". Derived fromCOLe and edMONds and allOY.

• 1938• The Welding Handbook, First Edition was printed and edited by

William Sparagen and D. S. Jacobus.• Pressure vessel industry began implementing the high production

value of Automatic Welding.• The German Shipbuilding Industry uses welding extensively toreduce the weight of warships and increase the overall size of theship. This restriction was put in place after World War I.

• K. K. Madsen of Denmark describes Gravity Welding as aspecialized electrode holder and the mechanism which will maintain

a covered electrode in contact with the workpiece.• A.F. Wall purchases Colmonoy and renames to Wall-Colmonoy(Detroit).

1939




• 1939• Floyd C. Kelly of General Electric publishes "Properties of Brazed 12% Chrome Steel" as

an early investigation of the strength of brazed joints.4Aluminum Spot Welding sawapplication in the Aviation Industry. He describes: – Single lap tensile specimens – 45 degree vee-type tensile specimen – Butt brazed tensile specimens.

• Aluminum Spot Welding saw application in the Aviation Industry.• Ultrasonic Fluxless soldering patented in Germany. Process is conceived in 1936.• Air Arc Gouging is developed (USA).• Stud Welding (Nelson Stud Welding Co.) used by the US Navy to reduce time installing

studs during fabrication of ships and aircraft carriers.

• 1940s• With World War II GTAW was found to be useful for welding magnesium in fighter planes,and later found it could weld stainless steel and aluminum.

• Canadian Welding Society (CWS) formed.• Exchequer, first all-welded ship built at Ingalls Shipyard in Mississippi.• J. Dearden and H. O'Neill (UK) discuss "Weldability" in terms of carbon equivalencies.• Sun Shipbuilding Company builds the world's largest ocean-going tanker, I. Van Dyck

(11650 DWT). This was the first large scale use of automatic welding applied in shipyardwork.• First mass soldering technique, Dip Soldering, is used for Printed Wiring Boards (PWB) to

keep up with the development of electronic equipment such as, Television, radios, etc.• Little advancement was made in brazing and there were no dry-hydrogen facilities, except

for laboratories, for brazing Stainless steel and there were no vacuum furnaces.• Germany was using 85Ag-15Mn brazing alloys as the best high temperature filler metal

available. Used for brazing hollow sheet metal blades used in the turbine engines and

stators.

1940




• 1940• Gas shielded metal arc welding developed by Hobart

and Devers at Battelle Memorial Institute.• 1941• Engineers at Northrup Aircraft Co. and Dow Chemical

Co. developed the GMAW process for weldingmagnesium, and later licensed it to Linde Co. with awater cooled, small diameter electrode wires using CVpower. Because of the high cost of inert gas, the cost

savings were not recognized until much later.• PLUTO - PipeLine Under The Ocean was created using

the Flash Weld (FW) process for 1000 miles of 3 inchdiameter pipe, to assist in the invasion of NormandyBeach, France. Once in place, the pipeline began

pumping 1 million gallons of petrol per day directly todepots deep in the French country side.• Friction Surfacing. H. Klopstock and A. R. Neelands "An

Improved Method of Joining and Welding Metals" BritishPatent 572789, October 1941.

• 1942




1942• Chief of Research, V. H. Pavlecka, and engineer Russ Meredith of Northrup Aircraft Inc.

designed the Gas Tungsten Arc Welding (GTAW) process to weld magnesium andstainless steel. Alternate names are TIG (tungsten inert gas) and Argonarc and Heliarc.Heliarc is the term originally applied to the GTAW process. (Patent Number 2274631, 24February 1942).

• The invention of GTAW was probably the most significant welding process developedspecifically for the aircraft industry and remained so until recently, with the Friction SirWeld process of the 1990's. Mr. Northrup of Northrup Aircraft Inc. was a visionary whowanted an all-welded aircraft (i.e., manufacturing costs, and lightweightness of theaircraft). Meredith was working from research of Devers and Hobart at General Electric(1920s) who had experimented with tungsten arcs in non-oxidizing atmospheres. The highreactivity of magnesium (Northrup's dream metal) would cause problems with moreconventional processes, so, Meredith to began developing a torch with better handlingcharacteristics and would use inert gas enshrouding tungsten. Thus, the Heli-arc process.

• From the Dec 1942 Welding Journal: "The full importance of arc welding on the future ofmagnesium alloys cannot be fully appreciated at this time but the fabrication of thesestrong light alloys has opened the possibilities that were not considered even a year ago.For the man in industry, this method of joining offers simplicity of structure, ease andspeed of fabrication and over-all economy."

• US Patent 2269369, Jan 6, 1942 issued to George Hafergut for Firecracker Welding.• Traveling 285 miles north of Edmonton Canada and barging 1100 miles north to the

Norman Well refinery a base camp was setup to build the Canadian Oil (CANOL) project.Working for 20 months, 1800 miles of pipeline was laid along side of 2000 miles of road.The last weld was laid on 1 February 1944. On 1 April 1945 the wells were shut down.

• Second Edition of the Welding Handbook was printed and issued.• SAW proves it worthiness during World War II with the building of the Liberty Ships.• G.L. Hopkins of Woolrich Arsenal defines the problem of cracking in alloy steels and

hydrogen in welding electrodes.

1943




• 1943• Union-Melt is now commonly referred to as Submerged Arc Welding

(SAW). The process used rods rather than wire filler metal and couldweld work pieces up to 2 -1/2 inches thick.

• Sciaky (USA) markets the three-phase resistance welder.• 1944• 1st Low-hydrogen electrodes used in fabrication of alloy armor tanks

vehicles by the Heil Corp in response to the chrome and nickelshortages from World War II for the U.S. Army.

• The Bureau of Navy Aeronautics designed and E. G. Budd Mfg. built

the "Conestoga", a stainless steel aircraft. Despite the success ofthe aircraft, aluminum and rivets became the influencing factor inaircraft design.

• 1945• After World War II, the Allies brought from Germany the alloy

combination, 85Ag-15Mn which has a 1760°F brazing temperature.

• ElectoBrazing is used for manufacturing shafts to gears.

• 1946




1946• Sprayweld Process (US Patent 2361962) issued to Wall-Colmonoy uses

an alloy powder spray which produces a smooth, welded deposits.• General Electric Co. Ltd (UK) invents the Cold Pressure Welding

Process.

• High Frequency (HF) stabilized AC tungsten-arc welding is used foraluminum alloys.

• 1947• The Final Report of a Board of Investigation, ordered by the Secretary of

the Navy, "To Inquire Into The Design and Methods of Construction ofWelded Steel Merchant Vessels, 15 July 1946" was issued.

• Canadian Welding Bureau was created as a division of the CanadianStandards Association

• The Austrian Welding Society is formed and publishes a monthlymagazine "Scheisstechnik"

• Nicrobraz, developed by Robert Peaslee of Wall-Colmonoy, is a 2500°Fnickel alloy braze filler metal used in hydrogen furnaces. Used forstainless steel fuel supply connecting injectors to injector pumps for 18cylinder reciprocating engines. The fledgling aircraft engine industryneeded something else for engines to experience a hot shutdownwithout blowing the silver braze filler metal out from the brazed joints.Typical alloy was 85Ag-15Mn (BAg-23).

1948




• 1948

The Ohio State University Board of Trustees establishedthe Department of Welding Engineering on January 1 as

the first of its kind for a Welding Engineering cirriculumat a University. OSU pioneered the Welding Engineeringthrough an emphasis in the Industrial EngineeringDepartment the previous nine years. The advantages ofthis engineering degree is 1) Enable satisfactory

administration of problems relating to education andresearch in the welding field. 2) Recognition is given to theWelding Engineer as an entity among applied sciences. 3)A degree is authorized which is descriptive of a particulardiscipline imposed in training for professional work in the

field. Air Reduction Company develops the Inert-Gas Metal-

Arc (MIG) process.




SIGMA Welding (Shielded Inert Gas Metal Arc) was developed to weldplate greater than1/8 inch instead of the "Heli-Arc" welding process. The arcis maintained in a shield of argon gas between the filler metal electrode andthe workpiece. No flux is used. Licensed by Linde Air Products Co.

•1948-1949

Curtiss-Wright Corporation looks at brazing as a strong, lightweightprocess for durable assemblies.

•1949

American Westinghouse introduces and markets welding machines usingSelenium Rectifiers.

US Navy uses inert-gas metal arc welding for aluminum hulls of 100 feet inlength.

•1950

The Kurpflaz Bridge in Germany was built as the first welded orthotropicdeck.




•1950s

Electron Beam (EB) welding process developed in France by J. A.Stohr of the French Atomic Energy Commission. First Public disclosurewas 1957.

Wave soldering is introduced to keep up with the demand of PrintedWiring Boards used in the electronics age.

Research on testing of brazed joint begins as serious endeavor for the

next ten years.•1950

Electroslag Welding (ESW) is developed at the E. O. Paton WeldingInstitute, Ukraine USSR.

Third Edition of the Welding Handbook is printed by AWS. Flash Butt Welding is the standard for welding rail line construction.




•1951

Russia use Electroslag Welding (ESW) process in production.

The Philip Roden Co. of Milwaukee Wisconsin announces theDryRod electrode oven. This oven is intended to provide acontrolled moisture environment of 0.2% moisture standard setforth by the government. This oven provides adjustabletemperature control of 200-550 F, vented and holding 350 pounds

of electrodes.

•1953

Modifying the Gas Metal Arc Welding (GMAW) process,Lyubavskii and Novoshilov used CO2 with consumable electrodes.

Resulted in hotter arc, uses higher current, and larger diameterelectrodes.

The Ohio State University established a Welding EngineeringCollege curriculum out of the Industrial Engineering Department.

•

•1957

http://www.weldinghistory.org/htmlhistory/link_osu_we.html







•1957 Flux Cored-Arc Welding (FCAW) patented and reintroduced byNational Cylinder Gas Co. Plasma Arc Welding (PAW) Process developed by Robert M.

Gage Russia, Britain, and USA independently develop a short-circuiting transfer for low-current low-voltage welding in acarbon dioxide atmosphere. Braze repair process for cracks in jet engine combustionchambers and transition ducts.1958 The Soviet Union introduced the Electroslag Welding (ESW) Process at theBrussels World Fair in Belgium. This welding process had been used since 1951in the USSR which was based on the concept and work of an American, R. K.

Hopkins. Perfected at the Paton Institute Laboratory in Kiev, Ukraine, USSRand the Welding Research Laboratory in Braitislava, Czechoslovakia. AWS Committee on Brazing and Soldering is formed to develop a test forevaluating strength of brazed joints. Robert Peaslee proposes a test in the

Welding Journal.




• 1959

Electroslag welding process was first used at the ElectromotiveDivision of General Motors in Chicago and was called the

"Electro-Molding Process".

Development of Inside-Outside Electrode which did not requirean external gas shielding - Innershield from Lincoln Electric Co.

• 1958-1959

Short Arc (Micro-wire Short Arc) developed from refined powersupplies and smaller diameter wires.

• 1960s

Pulsed Arc Welding...(more to follow)

Space Program is underway...(more to follow) Difficult to stabilize GTAW at below 15 amps, Microplasma is

developed to overcome the limitation.




1960

Development of a cold wall vacuum furnace.

First laser beam produced using a ruby crystal for the Light Amplification

Stimulated Emission Radiation (LASER).

Explosive welding is developed in USA.

Hughes Aircraft Company (Mainar) develops the first ruby laser

(springtime).

Bell Telephone Laboratories (Ali Javan) developed and presented the first

gas laser using neon and helium (fall time)

1962The Mercury Space Capsule is formed using inner and outer titanium

shell, seam welded together using a three-phase resistance welder by Sciaky.

1963

U.S.S. Thresher sinks off the coast of New Hampshire and by December,

the U.S. Navy charters the Submarine Safety Program (SUBSAFE) tocontrol the fabrication, inspection and quality control of submarine

construction. The presumed failure was with a silver-brazed piping joint, but

after the investigation, the whole welding and brazing program was suspect.

Included was the material properties of the welding and brazing filler

metals.

• 1965-1967




CO2 lasers are developed for cutting and welding.

• 1967

H. J. Clarke makes the following Predictions during the AWS PlummerLecture in Houston as he ties the current state of technology of welding tothe future of progress:

World's Population would be greater than 5 Billion.

Large scale farming of the ocean and fabrication of synthetic protein.

Controlled thermonuclear power as a source of energy.

General immunization against bacteria and virile infections, perfectedand available.

Primitive forms of life will created in the lab.

Automation will have advance for performance of menial chores andcomplicated functions.

Housewives would be ordering groceries and everyday items fromcentral stores linked to the home electronically. (!!!)




• Children will be receiving education at home - "either by television orwith personal teaching machines and programmed instructions"

Moon - mining and manufacture of propellant and on Mars,

permanent unmanned research stations.

Weather manipulation by the military.

Effective anti-ballistic missile defense in the form of air-launchedmissiles and directed energy beams.

Libraries will be "computer-run"

Gravity welding is introduced in Britain after its initial discovery byJapan.

• 1969

The Russian Welding Program in Space began by producingElectron Beam welds on SOYUZ-6. Welding an AMG6 and DM-20aluminum alloys with the Vulkan process. Sponsored by the E. O.Paton Welding Institute Academy of Science.

• 1970




As miniaturization developed from the pressure to increasecomponent densities, Surface Mount Technology is developed.This required new ways to make soldered joints, including thedevelopment of vapor phase, infrared, hot gas and other re-flow technologies.

First AWS International Brazing Conference including 24papers presented created much interest in the brazing

process.

BP discovers oil off the coast of Scotland.

• 1971

British Welding Institute (Houldcroft) adds oxidizing gas jetaround laser beam to develop laser cutting.

1973




• 1973

The American Astronauts used Electron

Beam welding process in June 1973 weldingAluminum Alloy 2219-T87, Stainless 304 andPure Tantalum.

Welding equipment manufacturers

concentrate on equipment refinement insteadof new processes.

Two Supertankers, Globtik Tokyo andGlobtik London (476025 DWT) were built forcarrying 153 million gallons (3 million barrels)of crude oil

1976




• 1976

First automotive production application of lasers weld begins with GeneralMotors Corporation, Dayton Ohio using two 1.25 kW CO2 lasers. for weldingvalve assemblies for emission control systems.

• 1977

The US Federal Highway Administration issues a moratorium of ElectroslagWelding (ESW) when cracks are discovered during an inspection of a bridge inPittsburgh, Pennsylvania on an interstate highway. Failure analysis was

conducted by Lehigh University on Interstate 79.• 1980

The Fort McHenry tunnel contract, for 750 Million Dollars, is awarded tobegin construction, completing Intestate 95 through Baltimore, Maryland. Thisis the largest tunnel of its kind, 180 feet at the bottom with two separate four

lane immersed tunnels removing 3.5 million cubic yards of dredge.

• 1983




• 1983

Homopolar pulse welding variation of the upset welding process researchbegins at the University of Texas at Austin at the Center forElectromechanics.

• 1987

Laser research begins a unique method for depositing complex metal alloys(Laser Powder Fusion).

• 1991

TWI of Cambridge England develops the Friction Stir Weld (FSW) processin its laboratory. This process differs from conventional rotary technologywhereby a hard, non consumable, cylindrical tool causes friction, plasticizingtwo metals into a Solid-State Bond. No shielding gas or filler metal isrequired. Metals joined successfully include, the 2XXX, 6XXX and 7XXX

series aluminum. NASA is the first US venture which welded the massive fueltank for the Space Shuttle.

Brazing Handbook (Fourth Edition) shows the data of the filler metal/basemetal failure transitions between 1T and 2T overlap and is the key for thedesign data (factor of safety).

1996




1996

Over 7,00,000 brazements are produced for the aircraft industry in the US

and Canada.

Over 132,010,00 units of brazed automotive parts are produce.

1999The Edison Welding Institute develops a solution to obtaining deeper

penetration of a GTA weld by introducing FLUX onto the surface of the weld.

This FLUX helps drive the welding arc heat deeper into the weld joint and

permits 300 percent more penetration.

2000

Magnetic Pulse Welding (MPW) is introduced by Pulsar Ltd. of Israel using

capacitive power as a solid state welding process. Discharging 2 Million amps

in less than 100 microseconds this process can create a metallurgical, a non-

metallurgical or a mechanical lock, depending on the substrate involved. No

heat affected zone (HAZ) is created since only a rise of 30oC occurs.

Tailored welded blanks of aluminum are used where spot welding was once

performed.

2000




Researchers from Argonne National Laboratory use the energy of

the x-ray to weld metal-matrix composite (Ti or Al / Al2O3 or

SiC) materials.

Diode laser welding, once limited to compact disks, laserprinters, and laser pointers, are now making their way to the

manufacturing floor. Welding Type 304 Stainless steel (0.024

inch), Titanium foil (0.005 inch thick) and laser brazing with a

silicon-bronze brazing wire.Conductive heat resistance seam welding (CHRSEW) is

developed. The process uses steel cover sheets placed on top of

aluminum butted together. Using conventional seam welding, the

heat generated from the steel forms a molten interface on the

aluminum and fusion is made at the butt joint. The steel covers

are then removed.

• 2001




2001AWS D17.1, "Specification for Fusion Welding for Aerospace

Applications" is published in March. The efforts of approximately 50individuals from a cross-section of the Aviation Industry and governmentproduces the first commercial aviation welding specification.

Flame brazing 5XXX aluminum alloys using non-corrosive flux.Sulzar Elbar introduces laser powder welding technology. Permits

rebuilding of substrate material (High Creep Resistance) and reproductionof the single crystal structure.

• 2002From Linde Gas in Germany, a Diode laser using process gases and "active-gascomponents" is investigated to enhance the "key-holing" effects for laser welding.The process gas, Argon-CO2, increases the welding speed and in the case of a diodelaser, will support the transition of heat conductivity welding to a deep welding, i.e.,'key-holing'. Adding active gas changes the direction of the metal flow within a weldpool and produces narrower, high-quality weld.

CO2 Lasers are used to weld polymers. The Edison Welding Institute is usingthrough-transmission lasers in the 230-980 nm range to readily form welded joints.Using silicon carbides embedded in the surfaces of the polymer, the laser is capableof melting the material leaving a near invisible joint line.

2003 2004 2005 Future developments.

ABOUT AWS




ABOUT AWS The American Welding Society (AWS) was founded in 1919 as a

multifaceted, nonprofit organization with a goal to advance the

science, technology and application of welding and related joining disciplines

• The Engineer ing

Societies Bui lding (lef t)

in New York Ci ty was thehome of AWS unti l 1961

when the Society moved

to the Uni ted Engineer ing

Center, also in New YorkCity.




From factory floor to high-rise construction, from

military weaponry to home products, AWS continues

to lead the way in supporting welding education andtechnology development to ensure a strong,

competitive and exciting way of life for all Americans.

• The Societymoved i ts

headquarters to

M iami in 1971

(left).




• The American Welding Society, in

conjunction with the Department of

Energy, has put together a vision that willcarry the welding industry through 2020.




• Technical Publications

• AWS offers over 300 books, charts, videos,

replicas, proceedings, and software. 160 AWS-

developed codes, recommended practices, and

guides are produced under strict AmericanNational Standards Institute (ANSI) procedures,

including one of the most consulted codes in the

world, D1.1 Structural Welding Code - Steel.

http://www.aws.org/foundation/





Foundation

• Founded in 1989, to support research andeducation in welding and related technologies. Itis committed to annually awarding fellowships todeserving graduate students for important

research in areas important to the requirementsof industry. Accordingly, each year the AWSFoundation administers six $20,000 grants -matched in kind by the participatinguniversities. The award of scholarships tovocational and undergraduate college students isalso a high priority and a student loan programhas also been developed to prepare students forwelding related careers.






• The Professional Program

The AWS Professional Program offers a broadspectrum of Technical Papers describing thelatest findings in welding research, processes andapplications. Special sessions and gatheringsexploring the boundaries of industry issues arealso significant features of the convention.Subjects cover an entire range of industryconcerns from the joining of space age materialsto production management techniques, testing,quality assurance and more.

Whi h ldi ( ) ill




Which welding process(es) will see an

increase in use and which will see a

decrease in use during the next decade?• There was much speculation, but

almost unanimously the process

chosen for decline was shielded metal

arc welding (SMAW). A very fewspeculated a decline in the use of gas

metal arc (GMAW) and gas tungsten arc

welding (GTAW). A significant group

felt the continuous wire processes

(FCAW, GMAW) would experience themost use. The GTAW process was the

next most mentioned. One of the

reasons stated for its increase was "the

need for high-quality work on thin

materials."




Welding Forges into the

Future

Where do you see the use of welding automation

heading in your industry?




• In what areas of welding do we need moreknowledge?

• Safety and Health. The industry needs more knowledge andawareness regarding the hazards of welding, according to the

respondents.

Welding of the newer grades of high-strength steels,high- alloy steels and heat treatable steels.

• We need to "keep up the 'how to weld' information with the increase in'new' alloys, which are becoming more difficult to weld."

Automation. A variety of topics relating to automation. Theseincluded training in computerization and automation; information onshort-run automation; and the need to create standard platforms for

welding equipment, robot controllers, sensing devices and otherautomation peripherals.

The basics While universities and institutions are doing basicresearch, they cannot tell you the best process and fastest speed for a

1Ž4-in. fillet weld."




• What are the strengths of the welding

industry? What are its weaknesses?

• What business improvements during thenext ten years would be in your company's

best interests?

• What has to be done in the future to keepthe welding industry healthy?

More than 50% of the respondents believe

improving the image of welding so top students

will be drawn to the industry and bettering trainingmethods for welders and welding engineers are the

keys to welding's future.

A ti i ti i i ti b t th




• Are you optimistic or pessimistic about the

future of your particular industry?

92% of respondents indicated they are at leastoptimistic about the future.

One respondent summed up his reasons thisway:

Metallics will be around for a long time andthey will need to be joined.

• Since time machines still exist only in the stories of H.




Since time machines still exist only in the stories of H.G. Wells and other works of science fiction, no one cantell us exactly how welding will fare in the 21st century.However, the people who responded to the WeldingJournal survey represent a cross section of fabricatorsof welded products and producers of weldingequipment and related products. Together they offer awide range of experience and knowledge. Answering

the questions separately, in their respective cities, theystill formed a consensus. They agree the future lookspromising for welding. It remains and will continue to bea productive, cost-effective manufacturing method.However, steps must be taken to bring more skilled

personnel into the industry, or changes must be madeto accommodate for the lack of skilled personnel (e.g.,welding automation). They also indicated the weldingindustry must embrace all of the modern-daytechnological tools to keep pace with the rest of the

world. .




LIQUID STATE PROCESSES

• Partial melting and fusion of joint

• Physical and mechanical changes taking place

• Can be with application of pressure or by additionof filler material

• Prior to joining, PREPARATION TO BE DONE

STANDARDS- AWS; ASTM-

TYPES OF GROOVES, JOINTS

NITC




Types of welds and symbols

• FILLET, SQUARE BUTT, SINGLE V,

• DOUBLE V, SINGLE U, DOUBLE U,

• SINGLE BEVEL BUTT, DOUBLE BEVEL BUTT,• SINGLE J BUTT, DOUBLE J BUTT,

• STUD, BEAD(EDGE OR SEAL), PLUG,

• SPOT, SEAM, MASHED SEAM,• STITCH, PROJECTION,

• FLASH, UPSET etc. (REFER sketches supplied)

NITC

Standard location of elements of weld symbol




Standard location of elements of weld symbol

L PS

Specification

process.

No tail-

SMAW

Other side of arrow

Near side of Arrow

Field weld

Weld all around

Size

Length of weld

Unwelded length

G- Grind C- Chip

F-File M-Machine

R- Rolling

Reference line

Finish symbol

Arrow connecting reference

line to arrow side of joint /to

edge prepared /member or

both

NITC

G f




ROOT

GROOVE ANGLE

Joint angle

Root Face

Groove face

NITC




WELD POSITIONS WELD MOVEMENTS

• FLAT

• HORIZONTAL

• VERTICAL

• OVERHEAD

• H

• O

• C

• J

• U• ZIGZAG

NITC

WELDING TERMINOLOGY



Slide 2 of 18

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http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WELD/tsld002.htm

http://www.staff.ncl.ac.uk/s.j.bull

http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WELD/index.htm







WELDING TECHNIQUES

FOREHAND BACKHAND

THIN

Same direction torch

Heat concentrated away from

bead

Even flow, rippled design

THICK

Opposite direction torch

Heat concentrated on bead

Broad bead

WELD POSITIONS




WELD POSITIONS

• FLAT HORIZONTAL VERTICAL OVERHEAD

NITC




WELD MOVEMENTS

OZIGZAG

L

ISTRAIGHT

Z

ASME P Material Numbers Explained

http://www.gowelding.com/wp/pnumbers.htm

http://www.gowelding.com/wp/pnumbers.htm




ASME has adopted their own designation for welding processes,

which are very different from the ISO definitions adopted by

EN24063.

Designation Description

OFW Oxyfuel Gas Welding

SMAW Shielded Metal Arc Welding (MMA)

SAW Submerged Arc Welding

GMAW Gas Metal Arc Welding (MIG/MAG)

FCAW Flux Cored Wire

GTAW Gas Tungsten Arc Welding (TIG)

PAW Plasma Arc Welding

Straight polarity = Electrode -ve

Reverse polarity = Electrode +ve

ASME F Numbers




F Number General Description

1 Heavy rutile coated iron powder electrodes :- A5.1 : E7024

2 Most Rutile consumables such as :- A5.1 : E60133 Cellulosic electrodes such as :- A5.1 : E6011

4 Basic coated electrodes such as : A5.1 : E7016 and E7018

5 High alloy austenitic stainless steel and duplex :- A5.4 : E316L-16

6 Any steel solid or cored wire (with flux or metal)2X Aluminium and its alloys

3X Copper and its alloys

4X Nickel alloys

5X Titanium6X Zirconium

7X Hard Facing Overlay

Note:- X represents any number 0 to 9

ASME A Numbers




These refer to the chemical analysis of the deposited weld and not

the parent material. They only apply to welding procedures in

steel materials.

A1 Plain unalloyed carbon manganese steels.

A2 to A4 Low alloy steels containing Moly and Chrome Moly

A8 Austenitic stainless steels such as type 316.

ASME Welding PositionsNote the welding progression (vertically upwards or downwards)




Note the welding progression, (vertically upwards or downwards),

must always be stated and it is an essential variable for both

procedures and performance qualifications.

Welding Positions For Groove welds:-

Welding PositionTest Position ISO and EN

Flat 1G PA

Horizontal 2G PCVertical Upwards Progression 3G PF

Vertical Downwards Progression 3G PG

Overhead 4G PE

Pipe Fixed Horizontal 5G PFPipe Fixed @ 45 degrees Upwards 6G HL045

Pipe Fixed @ 45 degrees Downwards 6G JL045




HORIZONTAL

VERTICAL UPWARDVERTICAL DOWNWARD




OVERHEAD




Multiple-pass layers. Weld layer sequence




G

for Groove

Welds

F

for Fillet

Welds



Dr. N. RAMACHANDRAN, NITC 104PREPARATION FOR PIPE WELDING

Welding Positions For Fillet welds:-




Welding PositionTest Position ISO and EN

Flat (Weld flat joint at 45

degrees)1F PA

Horizontal 2F PB

Horizontal Rotated 2FR PB

Vertical Upwards

Progression3F PF

Vertical Downwards

Progression

3F PG

Overhead 4F PD

Pipe Fixed Horizontal 5F PF




Welding Positions




g

QW431.1 and

QW461.2

Basically there are three

inclinations involved.

Flat, which includes

from 0 to 15 degrees

inclination15 - 80 degrees

inclination

Vertical, 80 - 90 degrees

For each of these

inclinations the weldcan be rotated from the

flat position to

Horizontal to overhead.

ELECTRODE IDENTIFICATION



ELECTRODE IDENTIFICATION

Arc welding electrodes are identified usingthe A.W.S, (American Welding Society)numbering system and are made in sizes

from 1/16 to 5/16 . An example would be a welding rodidentified as an 1/8" E6011 electrode.

The electrode is 1/8" in diameterThe "E" stands for arc welding electrode.

• Next will be either a 4 or 5 digit number stampedon the electrode The first two numbers of a 4




on the electrode. The first two numbers of a 4digit number and the first 3 digits of a 5 digitnumber indicate the minimum tensile strength (inthousands of pounds per square inch) of the weldthat the rod will produce, stress relieved.Examples would be as follows:

• E60xx would have a tensile strength of 60,000 psi

E110XX would be 110,000 psi• The next to last digit indicates the position the

electrode can be used in.• EXX1X is for use in all positions

• EXX2X is for use in flat and horizontal positions• EXX3X is for flat welding

• The last two digits together, indicate the




g g ,type of coating on the electrode and the

welding current the electrode can be usedwith. Such as DC straight, (DC -) DCreverse (DC+) or A.C.Type of coatings of the various electrodesare explained elsewhere.

• Examples of the type current each will workwith are as below.

• ELECTRODES AND CURRENTS USED

• EXX10 DC+ (DC reverse or DCRP) electrode positive




• EXX10 DC+ (DC reverse or DCRP) electrode positive.

• EXX11 AC or DC- (DC straight or DCSP) electrodenegative.

• EXX12 AC or DC-

• EXX13 AC, DC- or DC+


• EXX15 DC+

• EXX16 AC or DC+


• EXX20 AC ,DC- or DC+



• EXX28 AC or DC+

• CURRENT TYPES




• SMAW is performed using either AC orDCcurrent. Since DC current flows in one

direction, DC current can be DC straight,(electrode negative) or DC reversed (electrodepositive). With DC reversed,(DC+ OR DCRP)the weld penetration will be deep. DC straight(DC- OR DCSP) the weld will have a faster meltoff and deposit rate. The weld will have mediumpenetration.

Ac current changes it's polarity 120 times asecond by it's self and can not be changed ascan DC current.

ELECTRODE SIZE AND AMPS USEDThe table shown will serve as




Electrode Table

ELECTRODE

DIAMETER

AMP

RANGE

PLATE

1/16" 20 - 40 UP TO 3/16"

3/32" 40 - 125 UP TO 1/4"

1/8 75 - 185 OVER 1/8"

5/32" 105 - 250 OVER 1/4"

3/16" 140 - 305 OVER 3/8"

1/4" 210 - 430 OVER 3/8"

5/16" 275 - 450 OVER 1/2"

The table shown will serve asa basic guide of the amprange that can be used for

different size electrodes.These ratings can be differentbetween various electrodemanufactures for the samesize rod.

The type coating on theelectrode could effect theamperage range.Check manufacturer’s

recommended amperagesettings.

Note! The thicker the material

to be welded, the higher the

current needed and the larger

the electrode needed



Effects of expansion and




contraction

CONTROLLING DISTORTION




HEAT AFFECTED ZONE




L IQUID STATE PROCESSES




L IQUID STATE PROCESSES

• Partial melting and fusion of joint

• Physical and mechanical changes taking place

• Can be with application of pressure or by additionof filler material

• Prior to joining, PREPARATION TO BE DONE

STANDARDS- AWS; ASTM-

TYPES OF GROOVES, JOINTS

NITC

OXY ACETYLENE WELDING (OAW)



Oxyacetylene Welding (OAW)

The oxyacetylene welding process

uses a combination of oxygen and

acetylene gas to provide a hightemperature flame.

O t l W ldi (OAW)




Oxyacetylene Welding (OAW)

• OAW is a manual process in which the

welder must personally control the the torch

movement and filler rod application• The term oxyfuel gas welding outfit refers

to all the equipment needed to weld.

• Cylinders contain oxygen and acetylene gasat extremely high pressure.

Typical Oxyacetylene Welding

(OAW) St ti




(OAW) Station

O t l ldi




Oxy acetylene gas welding

STEPS for OAW

1 PREPARE THE EDGES AND MAINTAIN




1. PREPARE THE EDGES AND MAINTAIN

PROPER POSITION-………………………….(USE OF FIXTURES, CLAMPS)

2. OPEN ACETYLENE AND IGNITE

3. OPEN OXYGEN AND ADJUST FLAME

4. HOLD TORCH AT ABOUT 45O AND

FILLER METAL AT 30 TO 40 O

5. TOUCH FILLER ROD TO JOINT ANDCONTROL MOVEMENT

6. SINGLE BEAD MADE

• FOR DEEP JOINTS, MULTIPLE PASSES




• CLEANING EACH WELD BEAD ISIMPORTANT

• EQUIPMENT- WELDING TORCH-VARIOUS SIZES AND SHAPES

• CYLINDERS DIFFERENT THREADS,

ANCHORED AND NOT DROPPED

CAPABILITIES




CAPABILITIES

• LOW COST. MANUAL AND HENCE SLOW

• PORTABLE, VERSATILE AND ECONOMICALFOR LOW QUANTITY AND REPAIR WORKS

• FOR ALL FERROUS AND NONFERROUSMETALS

LIMITATIONS THICKNESS < 6 MM

• SKILL ESSENTIAL---FOR PIPE, PRESSUREVESSELS, LOAD BEARING STRUCTURALMEMBERS

O C li d




Oxygen Cylinders

• Oxygen is stored within cylinders of varioussizes and pressures ranging from 2000-2640 PSI. (Pounds Per square inch)

• Oxygen cylinders are forged from solidarmor plate steel. No part of the cylindermay be less than 1/4” thick.

• Cylinders are then tested to over 3,300 PSIusing a (NDE) hydrostatic pressure test.

O C li d




Oxygen Cylinders

• Cylinders are regularly

re-tested using

hydrostatic (NDE)

while in service

• Cylinders are regularly

chemically cleaned

and annealed to relieve“jobsite” stresses

created by handling .

Cylinder Transportation




Cylinder Transportation

• Never transport cylinders without the safety

caps in place

• Never transport with the regulators in place• Never allow bottles to stand freely. Always

chain them to a secure cart or some other

object that cannot be toppled easily.

Oxygen Cylinders




Oxygen Cylinders

• Oxygen cylinders

incorporate a thin metal

“pressure safety disk”

made from stainless steeland are designed to

rupture prior to the

cylinder becoming

damaged by pressure.

• The cylinder valve should

always be handled

carefully

Pressure Regulators for

Cylinders




Cylinders

• Reduce high storage

cylinder pressure to

lower working

pressure.

• Most regulators have a

gauge for cylinder

pressure and working pressure.

Pressure Regulators for

Cylinders




Cylinders

• Regulators are shut off

when the adjusting screw

is turn out completely.

• Regulators maintain a

constant torch pressure

although cylinder pressure

may vary

• Regulator diaphragms are

made of stainless steel

Pressure Regulators Gauges

Using a “Bourdon” movement




Using a Bourdon movement

• Gas entering the gauge fills a

Bourdon tube

• As pressure in the semicircular

end increases it causes the freeend of the tube to move

outward.

• This movement is transmitted

through to a curved rack whichengages a pinion gear on the

pointer shaft ultimately

showing pressure.

Regulator Hoses




Regulator Hoses

• Hoses are are fabricated from

rubber

• Oxygen hoses are green in

color and have right handthread.

• Acetylene hoses are red in

color with left hand thread.

• Left hand threads can beidentified by a groove in the

body of the nut and it may

have “ACET” stamped on it

Check Valves &

Flashback Arrestors




Flashback Arrestors

• Check valves allow gas

flow in one direction only

• Flashback arrestors are

designed to eliminate the possibility of an explosion

at the cylinder.

• Combination Check/

Flashback Valves can be placed at the torch or

regulator.

Acetylene Gas




Acetylene Gas

• Virtually all the acetylene distributed for welding and cutting use is

created by allowing calcium carbide (a man made product) to react

with water.

• The nice thing about the calcium carbide method of producingacetylene is that it can be done on almost any scale desired. Placed

in tightly-sealed cans, calcium carbide keeps indefinitely. For years,

miners’ lamps produced acetylene by adding water, a drop at a time,

to lumps of carbide.

• Before acetylene in cylinders became available in almost every

community of appreciable size produced their own gas from calcium

carbide.

Acetylene Cylinders




Acetylene Cylinders

• Acetylene is stored in cylinders specially designed for

this purpose only.

• Acetylene is extremely unstable in its pure form at

pressure above 15 PSI (Pounds per Square Inch)

• Acetone is also present within the cylinder to stabilize

the acetylene.

• Acetylene cylinders should always be stored in theupright position to prevent the acetone form escaping

thus causing the acetylene to become unstable.

Acetylene Cylinders




Acetylene Cylinders

• Cylinders are filled with a

very porous substance

“monolithic filler” to help

prevent from large pocketsof pure acetylene forming

• Cylinders have safety

(Fuse) plugs in the top and

bottom designed to melt at212° F (100 °C)

Acetylene Valves




Acetylene Valves

• Acetylene cylinder shut

off valves should only be

opened 1/4 to 1/2 turn

• This will allow thecylinder to be closed

quickly in case of fire.

• Cylinder valve wrenchesshould be left in place on

cylinders that do not

have a hand wheel.

Oxygen and Acetylene Regulator

Pressure Settings




Pressure Settings

• Regulator pressure may vary with different torchstyles and tip sizes.

• PSI (pounds per square inch) is sometimes shown as PSIG

(pounds per square inch -gauge) • Common gauge settings for cutting

– 1/4” material Oxy 30-35psi Acet 3-9 psi

– 1/2” material Oxy 55-85psi Acet 6-12 psi

– 1” material Oxy 110-160psi Acet 7-15 psi

• Check the torch manufactures data for optimum

pressure settings

Regulator Pressure Settings




• The maximum safe working pressure for

acetylene is 15 PSI !

Typical torch styles




Typical torch styles

• A small welding torch, with throttle valveslocated at the front end of the handle. Ideallysuited to sheet metal welding. Can be fittedwith cutting

• attachment in place of the welding headshown. Welding torches of this general designare by far the most widely used. They willhandle any oxyacetylene welding job, can befitted with multiflame (Rosebud) heads forheating applications, and accommodatecutting attachments that will cut steel 6 in.

thick.

• A full-size oxygen cutting torch which has allvalves located in its rear body. Another styleof cutting torch, with oxygen valves located atthe front end of its handle.



• Fuels

• The most commonly used fuel gas is acetylene

http://en.wikipedia.org/wiki/Acetylene




• The most commonly used fuel gas is acetylene.

• Other gases used are propylene, liquified petroleumgas (LPG), propane, natural gas, hydrogen, and

MAPP gas.

• Acetylene and gases that liquify under cylinder

pressure should only be used where it can be reliedon that the gas cylinder in use will always be vertical

with its valve on top.

• Note that there is not a single gas called

"oxyacetylene"; that misconception is sometimes

found among the unknowledgeable.

• Acetylene• Acetylene is the fuel first used for oxy-fuel welding and

remains the fuel of choice for repair work and general


http://en.wikipedia.org/wiki/Propylene

http://en.wikipedia.org/wiki/Liquified_petroleum_gas


http://en.wikipedia.org/wiki/Propane

http://en.wikipedia.org/wiki/Natural_gas

http://en.wikipedia.org/wiki/Hydrogen

http://en.wikipedia.org/wiki/MAPP_gas



http://en.wikipedia.org/wiki/Natural_gas










p gcutting and welding. Acetylene gas is shipped in special

cylinders designed to keep the gas dissolved.

• The cylinders are packed with various porous materials

(e.g. kapok fibre, diatomaceous earth, or, formerly,asbestos), then filled about half way with acetone.

• Acetylene dissolves into the acetone. This method is

necessary because above 207 kPa (30 lbf/in²) acetylene isunstable and may explode. There is about 1700 kPa (250lbf/in²) of pressure in the tank when full.

• Acetylene when burned with oxygen gives a

temperature of 3200 °C to 3500 °C (5800 °F

http://en.wikipedia.org/wiki/Kapok

http://en.wikipedia.org/wiki/Diatomaceous_earth

http://en.wikipedia.org/wiki/Asbestos

http://en.wikipedia.org/wiki/Acetone

http://en.wikipedia.org/wiki/Pascal

http://en.wikipedia.org/wiki/Pound-force_per_square_inch

http://en.wikipedia.org/wiki/Instability

http://en.wikipedia.org/wiki/Explosion

http://en.wikipedia.org/wiki/KPa

http://en.wikipedia.org/wiki/Pressure

http://en.wikipedia.org/wiki/Pressure

http://en.wikipedia.org/wiki/KPa

http://en.wikipedia.org/wiki/Explosion

http://en.wikipedia.org/wiki/Instability

http://en.wikipedia.org/wiki/Pound-force_per_square_inch

http://en.wikipedia.org/wiki/Pascal

http://en.wikipedia.org/wiki/Acetone

http://en.wikipedia.org/wiki/Asbestos

http://en.wikipedia.org/wiki/Diatomaceous_earth

http://en.wikipedia.org/wiki/Kapok

http://en.wikipedia.org/wiki/Oxygen

http://en.wikipedia.org/wiki/Celsius






temperature of 3200 C to 3500 C (5800 F

to 6300 °F), which is the highest temperatureof any of the commonly used gaseous fuels.

Its main disadvantage is its comparatively

high cost.

• As acetylene is unstable at a pressure

equivalent to being roughly 33 feet = 10

meters underwater, underwater cutting and

welding must use hydrogen instead of

acetylene.

• Hydrogen

• Hydrogen has a clean flame and is good for use on


http://en.wikipedia.org/wiki/Fahrenheit






http://en.wikipedia.org/wiki/Aluminum




y g galuminum. It can be used at a higher pressure than

acetylene and is• therefore useful for underwater welding. For smalltorches, hydrogen is often produced, along withoxygen, by electrolysis of water in an apparatuswhich is connected directly to the torch.

• Propane

• Propane does not burn as hot as acetylene, and so canonly be used for cutting, not for welding.

• Propylene

• Propylene is used in production welding.

MAPP gas

• MAPP gas is a registered product of the Dow



http://en.wikipedia.org/wiki/Electrolysis





http://en.wikipedia.org/wiki/Electrolysis




http://en.wikipedia.org/wiki/Dow_Chemical_Company





MAPP gas is a registered product of the Dow

Chemical Company.• It is liquified petroleum gas mixed with

methylacetylene- propadiene. It has the storage and

shipping characteristics of LPG and has a heat

value a little less than acetylene. Because it can be

shipped in small containers for sale at retail stores,

it is used by hobbyists. Other welding gasses that

develop comparable temperatures require special procedures for safe shipping and handling.

Typical startup procedures




http://en.wikipedia.org/wiki/Methylacetylene

http://en.wikipedia.org/wiki/Allene

http://en.wikipedia.org/wiki/Allene

http://en.wikipedia.org/wiki/Methylacetylene








• Verify that equipment visually appears safe ie: Hose

condition, visibility of gauges

• Clean torch orifices with a “tip cleaners” (a small wire

gauge file set used to clean slag and dirt form the torch

tip)

• Crack (or open) cylinder valves slightly allowing

pressure to enter the regulators slowly• Opening the cylinder valve quickly will “Slam” the

regulator and will cause failure.






• Never stand directly in the path of a regulator

when opening the cylinder

• Check for leaks using by listening for “Hissing” or

by using a soapy “Bubble” solution

• Adjust the regulators to the correct operating

pressure

• Slightly open and close the Oxygen andAcetylene valves at the torch head to purge any

atmosphere from the system.






• Always use a flint and steel spark lighter to light the

oxygen acetylene flame.

• Never use a butane lighter to light the flame

Flame Settings




Flame Settings

• There are three distinct types of oxy-acetylene

flames, usually termed:

– Neutral

– Carburizing (or “excess acetylene”)

– Oxidizing (or “excess oxygen” )

• The type of flame produced depends upon the

ratio of oxygen to acetylene in the gas mixture

which leaves the torch tip.

TYPES of FLAMES




• Neutral- with inner cone(30400C-33000C), outer envelope,

(21000C near inner cone, 12600C at tip)- high heating

• Reducing- Bright luminous inner cone, acetylene feather,

blue envelope

– Low temperature, good for brazing, soldering, flame

hardening

Hydrogen, methyl acetylene, propadiene also used as fuel.

• Oxidising- pointed inner cone, small and narrow outerenvelope

– Harmful for steels, good for Cu- Cu based alloys

NITC

OXY ACETYLENE WELDING (OAW)




(OAW)

Types of Flames

Neutral Reducing Oxidising

high heating low temperature good for Cu- Cu alloys

Pure Acetylene and Carburizing

Flame profiles




Flame profiles

Neutral and Oxidizing Flame

Profiles




Profiles

Flame definition




lame definition

• The neutral flame is produced when the ratio of oxygen to acetylene,

in the mixture leaving the torch, is almost exactly one-to-one. It’s

termed ”neutral” because it will usually have no chemical effect on the

metal being welded. It will not oxidize the weld metal; it will not cause

an increase in the carbon content of the weld metal.• The excess acetylene flame as its name implies, is created when the

proportion of acetylene in the mixture is higher than that required to

produce the neutral flame. Used on steel, it will cause an increase in

the carbon content of the weld metal.

• The oxidizing flame results from burning a mixture which containsmore oxygen than required for a neutral flame. It will oxidize or

”burn” some of the metal being welded.

Quiz time




Q

• The regulator diaphragm is often made from

_______?

A: reinforced rubberB: malleable iron

C: tempered aluminum

D: stainless steel

Quiz time




Q

• The hose nuts for oxygen and acetylene

differ greatly, because the acetylene hose

nut has.A: a left hand thread.

B: has a groove cut around it.

C: may have ACET stamped on it.D: All of the above.

Quiz time




Q

• An oxygen cylinder must be able to

withstand a ________ pressure of 3300 psi

(22753 kPa) to be qualified for service.A: atmospheric

B: hydrostatic

C: hydroscopicD: vapor

Quiz time




Q

• Why is the area above 15 psig often marked

with a red band on a acetylene low pressure

regulator ?• Answer

– Acetylene pressure above 15 psig is unstable

and should not be used

Quiz time




Q

• True or False ?

– A flint and steel spark lighter is the generally

used to light the oxyacetylene flame.

• Answer: True

Quiz time




Q

• Acetylene cylinder fuse plugs melt at a

temperature of ________° F or 100°C

• Answer

– 212°F

Quiz time




Q

• What is the maximum safe working gauge

pressure for acetylene gas?

A: 8 psig (55 kPa)

B: 15 psig (103 kPa)

C: 22 psig (152 kPa)

D: 30 psig (207 kPa)

Quiz time




Q

• The colour of and oxygen hose on a

oxyacetylene welding outfit is ______?

• Answer

– Green/Blue

Quiz time




Q

• The type of safety device is used on a

oxygen cylinder.

A: A fusible plugB: A check valve

C: A pressure safety disk

D: A spring loaded plug

Quiz time




Q

• True or False ?

– The regulator is closed when the adjusting

screw is turned out.

• Answer: True

Quiz time




Q

• The colour of acetylene hose on a

oxyacetylene welding outfit is ______?

• Answer

– Red

Quiz time




Q

• No part of an oxygen cylinder walls may be

thinner than _______?

A: 1/4”in (6.4 mm) B: 3/8”in (9.5 mm)

C: 3/16”in (4.8 mm)

D: 7/32”in (5.6 mm)

Quiz time




Q

• To prevent the occurrence of flashbacks, a

________ should be installed between

either the torch and hoses or regulators andhoses.

A: a two way check valve.

B: flame screen.C: flashback arrestor.

D: three way check valve.

Quiz time




• What type of safety device is used on a

acetylene cylinder.

A: A spring loaded plugB: A pressure safety disk

C: A fusible plug

D: A check valve

Quiz time




• Mixing _______ and water will produce

acetylene gas.

A: calcium carbideB: potassium carbonate

C: carbon dioxide

D: acetylene carbide

LIQUID STATE PROCESS




PARTIAL MELTING

BY STRIKING AN ARC

AFTER THE INVENTION OF ELECTRICITY

HOW ARC STRUCK?

ARC COLUMN THEORY



ARC WELDING




• ARC WELDING

ELECTRIC ARC




ELECTRIC ARC

WITHOUT ADDITIONAL EXTERNAL SOURCE

AUTOGENEOUS NONCONSUMABLE- CONSUMABLE

CARBON ARC WELDING (CAW) - OLDEST

METALLIC ARC WELDING (MAW)

COATING MATERIALS

ARC TO BE CREATED BY ELECTRICITY

WHEN? WITH THE INVENTION OF AC DYNAMO IN 1877

BEGINNING IN 1881- TO CONNECT PLATES OF STORAGE BATTERY

1886- BUTT WELDING TECHNIQUE WAS DEVELOPED




Q

BUTTED, CLAMPED HIGH CURRENT PASSED

AT THE JOINT, RESISTANCE OF METAL TO ELECTRIC CURRENT

PRODUCES HIGH HEAT- PIECES FUSED

ARC WELDING- MELTING AND FUSING OF METAL BY ELECTRODES

1ST BY N V BERNADO USING CARBON ELECTRODES




1ST BY N.V. BERNADO USING CARBON ELECTRODES

CONSISTANTLY IMPROVED

1895 N.G. SLAVIANOFF USED METALLIC ELECTRODES

1905 BARE ELECTRODES COATED—SHIELDING--- (SAW)

PORTABLE AND AUTOMATIC WELDING MACHINES

ARC WELDING PROCESSES




USE OF CONSUMABLE ELECTRODESSHIELDED METAL ARC WELDING(SMAW)

• SIMPLEST AND MOST VERSATILE

• ABOUT 50% OF INDUSTRIAL WELDINGBY THIS PROCESS

• CURRENT- 50 TO 300 A, < 10 KW

• AC/DC USED

• FOR THICKNESSES UPTO 19 –20 MM

SHIELDED METAL ARC WELDING(SMAW)



•Shielded metal arc welding (SMAW),

•Also known as Manual Metal Arc (MMA) welding

I f ll stick welding




• Informally as stick welding

is a manual arc welding process that uses a

consumable electrode coated in flux to lay the weld.

•An electric current, in the form of either alternating

current or direct current from a welding power supply, is

used to form an electric arc between the electrode and

the metals to be joined.

ELECTRICAL / IONIC THEORY

IONS FROM ANODE TO CATHODE,

AS METAL IONS ARE +VE CHARGED

ARC COLUMN THEORY

http://en.wikipedia.org/wiki/Arc_welding

http://en.wikipedia.org/wiki/Electrode

http://en.wikipedia.org/wiki/Flux_%28metallurgy%29

http://en.wikipedia.org/wiki/Current_%28electricity%29

http://en.wikipedia.org/wiki/Alternating_current


http://en.wikipedia.org/wiki/Direct_current

http://en.wikipedia.org/wiki/Welding_power_supply

http://en.wikipedia.org/wiki/Electric_arc

http://en.wikipedia.org/wiki/Metal







http://en.wikipedia.org/wiki/Current_%28electricity%29






ANODE +

CATHODE -

DC

•TOUCH AND THEN ESTABLISH A GAPTO BALANCE THE ATOMIC STRUCTURE

•IONS COLLIDE WITH GAS MOLECULES

•PRODUCES A THERMAL IONISATION LAYER

•IONISED GAS COLUMN – AS HIGH

RESISTANCE CONDUCTOR

•ON STRIKING CATHODE, HEAT GENERATED

•TERMED AS IONIC THEORY

•NOT COMPLETE IN EXPLAINING ARC

COLUMN THEORY •THUS, ELECTRON THEORY

ELECTRON THEORY

IONS FROM ANODE TO CATHODE

AS METAL IONS ARE +VE

CHARGED

ARC COLUMN THEORY




ANODE +

CATHODE -

CHARGED

-VELY CHARGED ELECTRONS

DISSOCIATED FROM CATHODE

MOVE OPPOSITE WITH HIGH

VELOCITY

DC(MASS- 9.1x 10-28 gm)

CAUSES HEAT IN ARC COLUMN RELEASES HEAT ENERGY IN

STRIKING THE ANODE

CALLED

ELECTRON IMPINGEMENT

AND

IONIC BOMBARDMENT




HIGH HEAT

MEDIUM HEAT

LOW HEAT

ANODE+

CATHODE -

ELECTRON IMPINGEMENT

IONIC BOMBARDMENT

MAGNETIC FLUX THEORY




• THE COLUMN NOT FLAIRINGDUE TO THE FLUX LINES AROUND

THE ARC COLUMN.

(Right hand Thumb Rule)

THIS COMPLETES THE ARC COLUMN THEORY

POLARITYAC

1. Currents higher thanthose of DCRP can beemployed (400 A to 500Afor 6 mm electrode)




Afor 6 mm electrode)

2. Arc cleaning of the basemetal

3. Normal penetration

4. Equal heat distribution

at electrode and job5. Electrode tip is colderas compared to that inDCRP

6. Average arc voltage in

argon atmosphere is16V

DCRP 1. Currents generally lessthan 125 amps (upto 6mm dia electrodes) toavoid overheating




avoid overheating

2. 2/3rd heat at electrodeand 1/3rd at the job

3. Least penetration

4. Average arc voltage on

argon atmosphere is19V

5. Chances of electrodeoverheating, melting andlosses

6. Better arc cleaningaction

DCSP1. Welding currents upto

1000 amps can beemployed for 6 mm




electrodes

2. 33.33% heat is generatedat the electrode and66.66% at the job.

3. Deep penetration

4. Average arc voltage in anargon atmsphere is 12 V

5. Electrode runs colder ascompared to AC or DCRP

6. No arc cleaning of base

metal




METALLURGY OF WELDING



During joining, localized heating occurs.

This leads to metallurgical and physical changes in materials welded.

Hence, study of:

1. Nature of welded joint

2. Quality and property of welded joint

3. Weldability of metals

4. Methods of testing welds

5. Welding design

6. Process selection- important

.




(2) Fusion Zone

(1) Base Metal

Structures: (1) SMALL (2) MEDIUM (3) LARGE

Properties of (2) and (3) important

(3) Heat Affected Zone (HAZ)



Arc column makes CRATER on

Gas shield




striking the surface- Temperature

above 1500 C

Flux + impurities- less dense. Floats as SLAG

Slag prevents heat loss- makes an evenly distribution

of heat radiation.

Preheating to receive the molten metal at an elevated temperature and

modify the structure. Not for M.S.

Locked in stresses due to heating and cooling- to be relieved by

PEENING, or other heat treatment processes.

MAGNETIC ARC BLOW -- FOR AC SUPPLY.




Current through conductor- magnetic Flux lines perpendicular tocurrent flow- apply Right hand Thumb Rule.

Three areas of magnetic field

1. Arc; 2. Electrode; 3. Work piece, when ground.

Forward pull of Arc column results, called as Magnetic Arc Blow.

EQUIPMENT



ELECTRODE COATING INGREDIENTS

• Slag forming ingredients- silicates of sodium, potassium, Mg,




Al, iron oxide, China clay, mica etc.

• Gas shielding- cellulose, wood, starch, calcium carbonate

• De-oxidising elements- ferro manganese, ferro silicon- torefine molten metal

• Arc stabilizing – calcium carbonate, potassium silicate,

titanates, Mg silicate etc.

• Alloying elements- ferro alloys, Mn, Mo., to impart specialproperties

• Iron powder- to improve arc behaviour, bead appearance

• Other elements - to improve penetration, limit spatter,improve metal deposition rates,

• As the weld is laid, the flux coating ofthe electrode disintegrates, giving offvapors that serve as a shielding gas

http://en.wikipedia.org/wiki/Shielding_gas





and providing a layer of slag, both ofwhich protect the weld area fromatmospheric contamination.

• Because of the versatility of theprocess and the simplicity of itsequipment and operation, shielded

metal arc welding is one of the world'smost popular welding processes.

• It dominates other welding processes in themaintenance and repair industry, usedextensively in the construction of steel




structures and in industrial fabrication.

• The process is used primarily to weld iron and steels (including stainless steel) but

aluminum, nickel and copper alloys can alsobe welded with this method.

• Flux-Cored Arc Welding (FCAW) , a

modification to SMAW is growing inpopularity

http://en.wikipedia.org/wiki/Iron

http://en.wikipedia.org/wiki/Steel

http://en.wikipedia.org/wiki/Stainless_steel


http://en.wikipedia.org/wiki/Nickel

http://en.wikipedia.org/wiki/Copper

http://en.wikipedia.org/wiki/Alloy

http://en.wikipedia.org/wiki/Flux-cored_arc_welding










http://en.wikipedia.org/wiki/Iron



(A).BARE ELECTRODE MOLTEN METAL TRANSFER

(B). LIGHT COATED ELECTRODE ARCACTION



Dr. N. RAMACHANDRAN, NITC 203Various welding electrodes and an electrode holder

SAFETY PRECAUTIONS• Uses an open electric arc, so

risk of burns – to be prevented




by protective clothing in theform of heavy leather gloves

and long sleeve jackets.

•The brightness of the weld area

can lead arc eye, in which

ultraviolet light causes the

inflammation of the cornea and

can burn the retinas of the eyes.

•Welding helmets with dark faceplates to be worn to prevent this

exposure

• New helmet models have been produced thatfeature a face plate that self-darkens uponexposure to high amounts of UV light

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http://en.wikipedia.org/wiki/Leather

http://en.wikipedia.org/wiki/Glove

http://en.wikipedia.org/wiki/Arc_eye

http://en.wikipedia.org/wiki/Ultraviolet_light

http://en.wikipedia.org/wiki/Cornea

http://en.wikipedia.org/wiki/Retina

http://en.wikipedia.org/wiki/Helmet

http://en.wikipedia.org/wiki/Helmet

http://en.wikipedia.org/wiki/Retina


http://en.wikipedia.org/wiki/Ultraviolet_light

http://en.wikipedia.org/wiki/Arc_eye

http://en.wikipedia.org/wiki/Glove

http://en.wikipedia.org/wiki/Leather

http://en.wikipedia.org/wiki/Protective_clothing




• To protect bystanders, especially inindustrial environments, transparent weldingcurtains often surround the welding area.

• These are made of a polyvinyl chloride plastic film, shield nearby workers fromexposure to the UV light from the electric arc,but should not be used to replace the filterglass used in helmets.

Arc eye, also known as arc flash or welder's flash orcorneal flash burns, is a painful condition sometimes

i d b ld h h f il d t d t

ARC EYE

http://en.wikipedia.org/wiki/Polyvinyl_chloride

http://en.wikipedia.org/wiki/Polyvinyl_chloride

http://en.wikipedia.org/wiki/Welder





experienced by welders who have failed to use adequateeye protection.It can also occur due to light from sunbeds, light

reflected from snow (known as snow blindness), water

or sand. The intense ultraviolet light emitted by the arc

causes a superficial and painful keratitis.

Symptoms tend to occur a number of hours

after exposure and typically resolve

spontaneously within 36 hours.It has been described as having sand poured

into the eyes.

Signs

Intense lacrimation Blepharospasm Photophobia


http://en.wikipedia.org/wiki/Eye

http://en.wikipedia.org/wiki/Sunbed

http://en.wikipedia.org/wiki/Snow

http://en.wikipedia.org/wiki/Snow_blindness

http://en.wikipedia.org/wiki/Water

http://en.wikipedia.org/wiki/Sand

http://en.wikipedia.org/wiki/Ultraviolet

http://en.wikipedia.org/wiki/Keratitis

http://en.wikipedia.org/wiki/Keratitis

http://en.wikipedia.org/wiki/Ultraviolet

http://en.wikipedia.org/wiki/Sand

http://en.wikipedia.org/wiki/Water

http://en.wikipedia.org/wiki/Snow_blindness

http://en.wikipedia.org/wiki/Snow

http://en.wikipedia.org/wiki/Sunbed

http://en.wikipedia.org/wiki/Eye


http://en.wikipedia.org/wiki/Lacrimation

http://en.wikipedia.org/wiki/Blepharospasm

http://en.wikipedia.org/wiki/Photophobia


http://en.wikipedia.org/wiki/Blepharospasm

http://en.wikipedia.org/wiki/Lacrimation




p

Fluorescein dye staining will reveal corneal ulcers

under blue light

Management

• Instill topical anaesthesia

• Inspect the cornea for any foreign body

• Patch the worse of the two eyes and prescribe analgesia

• Topical antibiotics in the form of eye drops or eyeointment or both should be prescribed for prophylaxisagainst infection

SUBMERGED ARC WELDING (SAW)


http://en.wikipedia.org/wiki/Fluorescein

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http://en.wikipedia.org/wiki/Analgesia

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http://en.wikipedia.org/wiki/Image:Submerged_arc_welder.lincoln.triddle.jpg






http://en.wikipedia.org/wiki/Image:Submerged_arc_welder_control_panel.lincoln.triddle.jpg




CONTROL PANEL

SUBMERGED ARC WELDING

http://en.wikipedia.org/wiki/Image:Submerged_arc_welder_control_panel.lincoln.triddle.jpg




DC-:




DC+ = Optimum Penetration DC - = Optimum deposition rate

Submerged Arc Welding (SAW)

• Is a common arc welding process

http://en.wikipedia.org/wiki/Welding





• Is a common arc welding process.

• A continuously fed consumable solid or tubular(metal cored) electrode used.

• The molten weld and the arc zone are protected

from atmospheric contamination by being―submerged‖ under a blanket of granular fusibleflux.

• When molten, the flux becomes conductive, and

provides a current path between the electrodeand the work

• Normally operated in the automatic ormechanized mode.

• Semi-automatic (hand-held) SAW guns with








pressurized or gravity flux feed delivery areavailable.

• The process is normally limited to the 1F, 1G, orthe 2F positions (although 2G position welds

have been done with a special arrangement tosupport the flux). Deposition rates approaching45 kg/h have been reported — this compares to~5 kg/h (max) for shielded metal arc welding.

• Currents ranging from 200 to 1500 A arecommonly used; currents of up to 5000 A havebeen used (multiple arcs).

• Single or multiple (2 to 5) electrode wirevariations of the process exist

• SAW strip-cladding utilizes a flat strip

http://en.wikipedia.org/wiki/Shielded_metal_arc_welding

http://en.wikipedia.org/wiki/Electrical_current

http://en.wikipedia.org/wiki/Electrical_current





electrode (e.g. 60 mm wide x 0.5 mmthick).

• DC or AC power can be utilized, andcombinations of DC and AC are commonon multiple electrode systems.

• Constant Voltage welding power supplies are most commonly used, however

Constant Current systems in combinationwith a voltage sensing wire-feeder areavailable.

SAW

• Fusion Welding Process





• Automatic / Semi Automatic• Arc Between Consumable Electrode And Work

• Arc Covered Under granular Flux

• Wire / Electrode Continuously Fed To Weld Pool

• Wire / Arc Under Flux Moves Along The Groove

• Wire, BM & Flux Close to Arc Melt Under Flux

• On Cooling Weld Metal Solidifies

• Molten Flux Forms Thick Slag Coating On Weld

SAW

Hopper

Power Source



•••••••••••••••• •••

+ – Wire

Flux

SlagWeld

Base Metal

Power SourceFlux

+

Arc

Flux For SAW



• Sodium Chloride

• Potassium Chloride

• Titanium Dioxide• Sodium Silicate

• Deoxidizing Agents

Types Of Flux



• Fused Flux

• Agglomerated Flux » Neutral Flux

» Active Flux

Types Of Flux



• Neutral Flux-Wire compatible to base metal

- Single flux suitable for several material

• Active Flux- Single flux suitable for specific application

- Wire may be different from basemetal

- To be welded within the recommended parameters

Function Of Flux In SAW• Stabilizes Arc

• Prevents contamination of weld metal



• Prevents contamination of weld metal

• Cleans the weld from unwanted impurities

• Increases Fluidity of molten metal

• Generates inert gas shielding while metal transfers

• Forms slag after melting & covers weld

• Allows deposited metal to cool slowly

• Compensates alloying elements Within the weld

• Eliminates spatter generation

• Helps in even & uniform bead finish

Baking Requirements For Flux



• Spread the loose Flux in a Tray Of baking Oven• Identify The Tray With The Quality/Grade Of Flux

• Bake Tray in an Oven Between 300° C to 350° C

• Baking Time 2 Hrs to 3 Hrs

• Reduce the temperature to 100 ° C to 150 ° C

• Hold the Flux at this temperature till use

Why Baking Flux?



• To remove the moisture (H2O)

• To avoid possible cracking of weld dueto H2

How Does Moist Flux GenerateCrack Within Weld?



• Moist Flux introduce atomic hydrogen at hightemperature in weld

• On cooling, atomic hydrogen try to formmolecules

• The reaction results in stresses and fine cracks

• Cracks occur within hardened metal - HAZ

• Known as “Hydrogen Embrittlement” or “UnderBead Crack” or Delayed Crack

Reuse Of Flux



• Flux May Be Reused Provided- Weld Not Highly Critical In Impact / Chemistry

- Reuse Limited To Maximum Twice

- All Slag Particles Are sieved & Removed

- Rebaked If not Remained In Hot

- Minimum 50% Fresh Flux Well Mixed

- Customer Spec. Doesn't Prohibit The Same

Types Of Power Source



• Thyrester – DC

• Rectifier – DC

• Motor Generator – DC

• Transformer - AC

Characteristic Of Power Source



Machine welding

Drooping – Cons. A Linear – Cons. V

V V

A A

V1

V2V2

V1

A2A1 A2A1

SAW Wire - Electrode

• Consumable Electrode / Wire



• Layer Wound On Spool / Coil

• CS & LAS Wires Coated with Cu

• Conducts Current and generates Arc

• Chemistry Compatible To Base Metal

• Grade Of Flux Can Be Same For CS & LAS

• Wire melts & deposited as filler in joint

Typical Welding Parameter



Srno

WireØ mm

Current A VoltageV

Speedmm/min

Dep. RatePer Arc Hr

Wire & Flux

1 1.6 200-300 22-26 750-1500 3 – 4 kgs CS wire

+

Neutral

Flux

2 2 250-350 24-26 750-1250 3- 4.5 kgs

4 2.5 300-350 25-27 750-1250 4 – 4.5 kgs

5 3 400-500 28-30 500-100 5 – 5.5 kgs

6 4 550-650 30-32 400-750 5.5 - 7 kgs

7 5 600-800 30-34 350-700 6 - 8 kgs

Important parameters




Current

Wave Offset

Wave Balance

Frequency

•Wave Offset Variation

w e r

Level 150%,50%

Level 2+75%,-25%

Level 3+25%,-75%




time

C u r r e n t , V o l t a g e ,

P o w

* Wave offset refers to the shift in the amplitude direction. Equal amplitude in positiveand negative side is referred as zero offset whereas an increase in wave offset implies

that the positive amplitude is increased from its equilibrium position of 50% andproportionate decrease in negative amplitude from its equilibrium position of 50% anddecrease in wave offset implies that the positive amplitude is decreased from itsequilibrium position of 50% and proportionate increase in negative amplitude from itsequilibrium position of 50%

•Wave Balance VariationLevel 1+50, -50

Level 2+75, -25

Level 3+25, -75




time

C u r r e n t , V o

l t a g e ,

P o w e r

Wave balance refers to the amount of time the waveform spends inDC+ part of cycle but the amplitude will be same.

•Effect of Frequency

Level 1Low

Level 2medium

Level 3High




time

C u r r e n t , V o l t a g e ,

P o w e r

Frequency refers to shift of peak current with respect to the zero crossing.

Here we observe that at lower frequency shift of peak current withrespect to the zero crossing is less than in comparison to higherfrequency. So Penetration & deposition will be more at lower frequency.

Important Terminology used inCritical SAW



• Preheating

• Post Heating or Dehydrogenation

• Intermediate Stress leaving• Inter pass Temperature

• Post Weld Heat Treatment

What Is Preheating?

• Heating the base metal along the weld joint to a



g g j

predetermined minimum temperature

immediately before starting the weld.

• Heating by Oxy fuel flame or electric resistant

coil

• Heating from opposite side of welding wherever

possible

• Temperature to be verified by thermo chalks

prior to starting the weld

Why Preheating?

• Preheating eliminates possible cracking of weld and



HAZ

• Applicable to

-Hardenable low alloy steels of all thickness

-Carbon steels of thickness above 25 mm.

-Restrained welds of all thickness

• Preheating temperature vary from 75°C to 200°C

depending on hardenability of material, thickness & joint restrain

How does Preheating EliminateCrack?



• Preheating promotes slow cooling of weld and

HAZ

• Slow cooling softens or prevents hardening of

weld and HAZ

• Soft material not prone to crack even in

restrained condition

What Is Post Heating?

• Raising the pre heating temperature of the weld joint to



a predetermined temperature range (250° C to 350° C)for a minimum period of time (3 Hrs) before the weldcools down to room temperature.

• Post heating performed when welding is completed or

terminated any time in between.

• Heating by Oxy fuel flame or electric resistant coil

• Heating from opposite side of welding wherever possible

• Temperature verified by thermo chalks during the period

Why Post Heating?

• Post heating eliminates possible delayed cracking



g p y g

of weld and HAZ

• Applicable to

-Thicker hardenable low alloy steels-Restrained hardenable welds of all

thickness

• Post heating temperature and duration dependson hardenability of material, thickness & joint

restrain

How does Post Heating EliminateCrack?

• SAW introduces hydrogen in weld metal



• Entrapped hydrogen in weld metal induces

delayed cracks unless removed before cooling to

room temperature

• Retaining the weld at a higher temperature for a

longer duration allows the hydrogen to come out

of weld

What Is Intermediate StressRelieving?

• Heat treating a subassembly in a furnace to a



predetermined cycle immediately on completionof critical restrained weld joint / joints withoutallowing the welds to go down the pre heat

temperature. Rate of heating, Soakingtemperature, Soaking time and rate of coolingdepends on material quality and thickness

• Applicable to

Highly restrained air hardenable material

Why Intermediate StressRelieving?

• Restrained welds in air hardenable steel highly



prone to crack on cooling to room temperature.

• Cracks due to entrapped hydrogen and built in

stress

• Intermediate stress relieving relieves built in

stresses and entrapped hydrogen making the jointfree from crack prone

What Is Inter- Pass Temperature?• The temperature of a previously layed weld bead



immediately before depositing the next bead overit

• Temperature to be verified by thermo chalk prior

to starting next bead

• Applicable to

Stainless Steel

Carbon Steel & LAS with minimum impact

Why Inter Pass Temperature?



• Control on inter pass temperature avoids overheating, there by

-Refines the weld metal with fine grains

-Improves the notch toughness properties-Minimize the loss of alloying elements in

welds

-Reduces the distortion



Material applications




• Carbon steels (structural and vesselconstruction);

• Low alloy steels;

• Stainless Steels;• Nickel-based alloys;

• Surfacing applications (wearfacing, build-

up, and corrosion resistant overlay ofsteels).

Advantages of SAW




• High deposition rates (over45 kg/h) have beenreported;

• High operating factors in mechanizedapplications;

• Deep weld penetration;• Sound welds are readily made (with good

process design and control);• High speed welding of thin sheet steels at over

2.5 m/min is possible;• Minimal welding fume or arc light is emitted.

Limitations of SAW

f ( )




• Limited to ferrous (steel or stainless steels) andsome nickel based alloys;

• Normally limited to the 1F, 1G, and 2F positions;• Normally limited to long straight seams or

rotated pipes or vessels;• Requires relatively troublesome flux handling

systems;• Flux and slag residue can present a health &

safety issue;• Requires inter-pass and post weld slag removal.

Key SAW process variables

• Wire Feed Speed (main factor in welding current control);

A V lt




• Arc Voltage;• Travel Speed;• Electrical Stick-Out (ESO) or Contact Tip to Work (CTTW);• Polarity and Current Type (AC or DC).

Other factors

• Flux depth/width;• Flux and electrode classification and type;• Electrode wire diameter;• Multiple electrode configurations.



Shielded Metal Arc Welded plate (distortion 11.3

)

s h r i n k a g e




Transverse shrinkage

L o n g i t u d i n a l s

Angular

distortion

Bowing

X X

Y

x

y




m

Y

Y

TENSIONCOMPRESSION

x

(b)

X

y

COMPRESSION

base

metal

TENSION

With External

Constraint

X

(c)

Y

(a)

Typical distribution of residual stresses (b) Longitudinal and (c ) Transverse tothe butt-weld line (a)

50°

6

Number of weld

pass Carriage speed

(m/min)




Weld passes for Submerged Arc Welding

6

1

25 2

3

4

5

1

1 0.5

2 0.5

3 0.32

4 0.24

5 0.22

6 0.22




Submerged Arc Welded plate (distortion 5.08 )




Ultrasonic measuring area on SMAW plate




Ultrasonic measuring area on SAW plate (half of the test plate)

FCAW




Atomic hydrogen welding

• Atomic hydrogen welding (AHW) is an arc welding process that uses anarc between two metal tungsten electrodes in a shielding atmosphere ofhydrogen The process was invented by Irving Langmuir in the course of his


http://en.wikipedia.org/wiki/Tungsten



http://en.wikipedia.org/wiki/Irving_Langmuir









hydrogen. The process was invented by Irving Langmuir in the course of hisstudies in atomic hydrogen. The electric arc efficiently breaks up thehydrogen molecules, which later recombine[dubious – discuss] withtremendous release of heat, greater than any other chemicalreaction[dubious – discuss], reaching temperatures from 3400 to 4000 °C.This device may be called an atomic hydrogen torch, nascent hydrogentorch or Langmuir torch. The process was also known as Arc-Atom

welding.• The heat produced by this torch is sufficient to melt and weld tungsten

(3422 °C), the most refractory metal. Because of the atmosphere ofhydrogen, metals are protected from contamination by carbon, nitrogen, oroxygen which can severely damage the properties of many metals.[dubious – discuss]

• In atomic hydrogen welding, filler metal may or may not be used. In this

process, the arc is maintained entirely independent of the work or partsbeing welded. The work is a part of the electrical circuit only to the extentthat a portion of the arc comes in contact with the work, at which time avoltage exists between the work and each electrode.

• It is a welding process wherein coalescence (fusion) is

produced by heating the job with an electric arc




http://en.wikipedia.org/wiki/Wikipedia:Disputed_statement

http://en.wikipedia.org/wiki/Talk:Atomic_hydrogen_welding




http://en.wikipedia.org/wiki/Refractory_metal

http://en.wikipedia.org/wiki/Carbon

http://en.wikipedia.org/wiki/Nitrogen




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http://en.wikipedia.org/wiki/Filler_metal






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produced by heating the job with an electric arcmaintained between two tungsten electrodes in anatmosphere of hydrogen, which also acts as a shieldinggas. Filler rod and pressure mayor may not be applieddepending upon job conditions.

• PRINCIPLE

• Atomic hydrogen welding possesses the features of botharc and flame welding processes. The job does not forma part of the electrical circuit. The arc remains only

between two tungsten electrodes and the edge of the arcflame is used to weld the work pieces




ATOMIC HYDROGEN WELDING TORCH

• Atomic Hydrogen Welding (AHW) issimilar to GTAWand uses an arc betweentwo tungsten or carbon electrodes in ashielding atmosphere of hydrogen




shielding atmosphere of hydrogen.Therefore, the work piece is not part of theelectrical circuit.

GAS TUNGSTEN ARC WELDING (GTAW)



GTAW

http://en.wikipedia.org/wiki/Image:GTAW_welding.jpg




GTAW• Fusion Welding Process

• Arc Between Non-Consumable Tungsten

Rod And Work

http://en.wikipedia.org/wiki/Image:GTAW.png

http://en.wikipedia.org/wiki/Image:GTAW_welding.jpg

http://en.wikipedia.org/wiki/Image:GTAW.png




Rod And Work• Arc & Weld Pool Shielded By Argon/Gas

• Filler Wire Separately Added To Weld Pool

• Welding Torch & Tungsten Rod Cooled byFlow OF Argon / Cooling Water

GAS TUNGSTEN ARC WELDING (GTAW)

• ELECTRODE NOT CONSUMED

• TUNGSTEN ELECTRODES USED

ARGON HEAVIER FOR NARROW AND LIMITED




• ARGON- HEAVIER FOR NARROW AND LIMITED

EXPANSION,WIDER, DEEPER PUDDLE

• HELIUM FOR EVEN EXPANSIONLIMITED

STRESS BUILDUP

• MORE He, MORE HEAT IN ARC

• Ar-He MIX FOR AUTOMATIC GTAW

• Ar- CO2 FOR CARBON STEELS, ECONIMICAL,

INCREASES WETTING ACTION• GTAW TORCH- WATER OR AIR COOLED

CONSTANT CURRENT SOURCE.(IIIr TO SMAW)

GTAW Equipment &Accessories

• Power Source – Inverter, Thyrister, Rectifier,

Generator




Generator• High Frequency Unit

• Water Cooling System

• Welding Torch- (Ceramic Cup, Tungsten Rod, Collet,

Gas-lens) • Pedal Switch

• Argon Gas Cylinder

• Pressure Gauge, Regulator, Flow Meter

• Earthing Cable With Clamp



Dr. N. RAMACHANDRAN, NITC 267• A TYPICAL GTAW WELDING SET UP

Equipment & Accessories

Flow Meter

Pressure Regulator

Tungsten Rod



Dr. N. RAMACHANDRAN, NITC 268 – +

Argon Gas In

Welding Cable & CoolingWater In Tube

HF Unit &Water Cooling

System

Argon Cylinder Cooling Water In

Cooling Water Out Argon Shielding

Tungsten Rod

Power Source

Work

Arc

+

High FrequencyConnection

SolenoidValve

Ceramic Cup

Pedal Switch

Gas Lens

Equipment

http://en.wikipedia.org/wiki/Image:TIG_torch_breakdown.JPG

http://en.wikipedia.org/wiki/Image:TIG_torch-accs..JPG




GTAW torch, disassembledGTAW torch with variouselectrodes, cups, collets and gasdiffusers

Gas tungsten arc welding (GTAW),commonly known as Tungsten Inert Gas

(TIG) welding• Is an arc welding process that uses a

nonconsumable tungsten electrode to produce


http://en.wikipedia.org/wiki/Image:TIG_torch-accs..JPG










nonconsumable tungsten electrode to producethe weld.

• The weld area is protected from atmosphericcontamination by a shielding gas (usually an

inert gas such as argon), and a filler metal isnormally used, though some welds, known asautogenous welds, do not require it.

• A constant current welding power supply

produces energy which is conducted across thearc through a column of highly ionized gas andmetal vapors known as a plasma.

• Most commonly used to weld thin sectionsof stainless steel and light metals such asaluminum, magnesium, and copper alloys.

• The process grants the operator greater

control over the weld than competingprocedures such as shielded metal arc




http://en.wikipedia.org/wiki/Argon


http://en.wikipedia.org/wiki/Plasma

http://en.wikipedia.org/wiki/Plasma







http://en.wikipedia.org/wiki/Aluminium

http://en.wikipedia.org/wiki/Magnesium











control over the weld than competingprocedures such as shielded metal arcwelding and gas metal arc welding, allowingfor stronger, higher quality welds.

• GTAW is comparatively more complex and

difficult to master, and furthermore, it issignificantly slower than most other weldingtechniques.

• A related process, plasma arc welding, uses

a slightly different welding torch to create amore focused welding arc and as a result isoften automated.

GTAW system setup



http://en.wikipedia.org/wiki/Gas_metal_arc_welding

http://en.wikipedia.org/wiki/Plasma_arc_welding

http://en.wikipedia.org/wiki/Plasma_arc_welding




http://en.wikipedia.org/wiki/Image:GTAW_setup.png




Applications

• Aerospace industry is one of the primary users of gastungsten arc welding. The process is used in a number of otherareas.

• Many industries use GTAW for welding thin workpieces,

http://en.wikipedia.org/wiki/Image:GTAW_setup.png




Many industries use GTAW for welding thin workpieces,especially nonferrous metals.

• It is used extensively in the manufacture of space vehicles, andis also frequently employed to weld small-diameter, thin-walltubing.

• Is often used to make root or first pass welds for piping ofvarious sizes.

• In maintenance and repair work, the process is commonly usedto repair tools and dies, especially components made ofaluminum and magnesium.

• Because the welds it produces are highly resistant to corrosionand cracking over long time periods, GTAW is the weldingprocedure of choice for critical welding operations like sealingspent nuclear fuel canisters before burial.

QualityGTAW ranks the highest in terms of the

quality of weld produced.Operation must be with free from oil,

moisture, dirt and other impurities, as

these cause weld porosity and

consequently a decrease in weld

strength and quality.

To remove oil & grease, alcohol or

http://en.wikipedia.org/wiki/Nuclear_fuel

http://en.wikipedia.org/wiki/Nuclear_fuel

http://en.wikipedia.org/wiki/Image:08-TIG-weld.jpg




g ,

similar commercial solvents used, while

a stainless steel wire brush or chemical

process remove oxides from the

surfaces of metals like aluminum.

Rust on steels removed by first gritblasting the surface and then using a

wire brush to remove imbedded grit.

These steps important when DCEN

used, because this provides no cleaning

during the welding process, unlike

DCEPor AC.To maintain a clean weld pool during welding, the shielding gas flow should besufficient and consistent so that the gas covers the weld and blocks impurities inthe atmosphere. GTA welding in windy or drafty environments increases theamount of shielding gas necessary to protect the weld, increasing the cost andmaking the process unpopular outdoors.

• Because of GTAW's relative difficulty and theimportance of proper technique, skilledoperators are employed for importantapplications.

• Low heat input caused by low welding


http://en.wikipedia.org/wiki/Grit_blasting





http://en.wikipedia.org/wiki/Image:08-TIG-weld.jpg




Low heat input, caused by low weldingcurrent or high welding speed, can limitpenetration and cause the weld bead to liftaway from the surface being welded.

• If there is too much heat input, the weldbead grows in width while the likelihood ofexcessive penetration and spatter increase.

• If the welder holds the welding torch too farfrom the workpiece, shielding gas is wastedand the appearance of the weld worsens.

• If the amount of current used exceeds thecapability of the electrode, tungsteninclusions in the weld may result. Known astungsten spitting, it can be identified with

radiography and prevented by changing thet f l t d i i th l t d

http://en.wikipedia.org/wiki/Radiography





radiography and prevented by changing thetype of electrode or increasing the electrodediameter.

• If the electrode is not well protected by the

gas shield or the operator accidentally allowsit to contact the molten metal, it can becomedirty or contaminated. This often causes thewelding arc to become unstable, requiring

that electrode be ground with a diamondabrasive to remove the impurity.

• GTAW welding torches designed for either automaticor manual operation and are equipped with coolingsystems using air or water. The automatic andmanual torches are similar in construction, but themanual torch has a handle while the automatic torch

normally comes with a mounting rack.Th l b t th t li f th h dl d





normally comes with a mounting rack. • The angle between the centerline of the handle and

the centerline of the tungsten electrode, known asthe head angle, can be varied on some manualtorches according to the preference of the operator .

• Air cooling systems are most often used for low-current operations (up to about 200 A), while watercooling is required for high-current welding (up toabout 600 A).

• The torches are connected with cables to the powersupply and with hoses to the shielding gas sourceand where used, the water supply.

• The internal metal parts of atorch are made of hard alloysof copper or brass in order totransmit current and heateffectively.

• The tungsten electrode mustb h ld fi l i th t f

http://en.wikipedia.org/wiki/Ampere

http://en.wikipedia.org/wiki/Ampere


http://en.wikipedia.org/wiki/Brass







e tu gste e ect ode ustbe held firmly in the center ofthe torch with anappropriately sized collet,and ports around the

electrode provide a constantflow of shielding gas.• The body of the torch is

made of heat-resistant,insulating plastics coveringthe metal components,providing insulation fromheat and electricity to protectthe welder.

GTAW TORCH

http://en.wikipedia.org/wiki/Collet


http://en.wikipedia.org/wiki/Collet




Tungsten Rod

Ceramic Cup

Arc

Argon Gas Inlet

Cooling Water Outlet

Cooling Water Inlet Tube with cable

Base Metal

Torch Handle Cap with collet ForHolding Tungsten

Argon Shielding Gas

Earthing Cable

• The size of the welding torch nozzle dependson the size of the desired welding arc, and

the inside diameter of the nozzle is normally

at least three times the diameter of the

electrode




electrode.

• The nozzle must be heat resistant and thus is

normally made of alumina or a ceramic

material, but fused quartz, a glass-likesubstance, offers greater visibility.

• Devices can be inserted into the nozzle for

special applications, such as gas lenses or

valves to control shielding gas flow and

switches to control welding current.

Power supply • GTAW uses a constant

current power source,

meaning that the current (and

thus the heat) remains

relatively constant, even if

the arc distance and voltage

http://en.wikipedia.org/wiki/Alumina

http://en.wikipedia.org/wiki/Alumina

http://en.wikipedia.org/wiki/Image:Welding_power_supply-Miller-Syncrowave350LX-front-triddle.jpg




g

change.

• This is important because

most applications of GTAW

are manual or semiautomatic,

requiring that an operatorhold the torch.

• Maintaining a suitably steady

arc distance is difficult if a

constant voltage power

source is used instead, sinceit can cause dramatic heat

variations and make welding

more difficult.

• The preferred polarity of the GTAW system depends largely onthe type of metal being welded.

• DCEN is often employed when welding steels, nickel, titanium,and other metals. It can also be used in automatic GTA weldingof aluminum or magnesium when helium is used as a shielding

gas. The negatively charged electrode generates heat byemitting electrons which travel across the arc, causing thermal

http://en.wikipedia.org/wiki/Image:Welding_power_supply-Miller-Syncrowave350LX-front-triddle.jpg



http://en.wikipedia.org/wiki/Titanium







emitting electrons which travel across the arc, causing thermalionization of the shielding gas and increasing the temperatureof the base material. The ionized shielding gas flows toward theelectrode, not the base material, and this can allow oxides tobuild on the surface of the weld.

• DCEP is less common, and is used primarily for shallow weldssince less heat is generated in the base material. Instead offlowing from the electrode to the base material, as in DCEN,electrons go the other direction, causing the electrode to reachvery high temperatures. To help it maintain its shape andprevent softening, a larger electrode is often used. As the

electrons flow toward the electrode, ionized shielding gas flowsback toward the base material, cleaning the weld by removingoxides and other impurities and thereby improving its qualityand appearance.

• AC commonly used when welding aluminum andmagnesium manually or semi-automatically, combinesthe two direct currents by making the electrode andbase material alternate between positive and negativecharge. This causes the electron flow to switchdirections constantly, preventing the tungsten electrode

from overheating while maintaining the heat in the basematerial This makes the ionized shielding gas








g gmaterial. This makes the ionized shielding gasconstantly switch its direction of flow, causingimpurities to be removed during a portion of the cycle.

• Some power supplies enable operators to use an unbalancedalternating current wave by modifying the exact percentage of timethat the current spends in each state of polarity, giving them morecontrol over the amount of heat and cleaning action supplied bythe power source.

• In addition, operators must be wary of rectification, inwhich the arc fails to reignite as it passes from straight

polarity (negative electrode) to reverse polarity (positiveelectrode).

• To remedy the problem, a square wave power supplycan be used, as can high frequency voltage toencourage ignition.

Tungsten Rod

• Non Consumable Electrode.

• Maintains Stable Arc

Tungsten Rod

ISO Colour Code

http://en.wikipedia.org/wiki/Rectification_%28electricity%29

http://en.wikipedia.org/wiki/Square_wave

http://en.wikipedia.org/wiki/Square_wave

http://en.wikipedia.org/wiki/Rectification_%28electricity%29




Maintains Stable Arc

• Tip to be Ground to a cone Shape of 60º to 30ºangle

• Thoriated Tungsten for General Application,Zerconiated Tungsten for AluminiumWelding

• Sizes :- 2, 2.4 & 3 mm Ø

Ground to

300

-60ºangle

ISO

Class ISO Color AWS Class

AWS

Color Alloy [18]

WP Green EWP Green None

WC20 Gray EWCe-2 Orange ~2% CeO2

•The electrode used in GTAW ismade of tungsten or a tungsten alloy,because tungsten has the highestmelting temperature among metals,at 3422 °C.

• The electrode is not consumedduring welding though some erosion

http://en.wikipedia.org/wiki/Gas_tungsten_arc_welding

http://en.wikipedia.org/wiki/Ceria
















WL10 Black EWLa-1 Black ~1% LaO2

WL15 Gold EWLa-1.5 Gold ~1.5% LaO2

WL20 Sky-blue EWLa-2 Blue ~2% LaO2

WT10 Yellow EWTh-1 Yellow ~1% ThO2

WT20 Red EWTh-2 Red ~2% ThO2

WT30 Violet ~3% ThO2

WT40 Orange ~4% ThO2

WY20 Blue ~2% Y2O

3

WZ3 Brown EWZr-1 Brown ~0.3% ZrO2

WZ8 White ~0.8% ZrO2

during welding, though some erosion(called burn-off) can occur.•Electrodes can have either a cleanfinish or a ground finish—clean finishelectrodes have been chemicallycleaned, while ground finishelectrodes have been ground to auniform size and have a polishedsurface, making them optimal forheat conduction.

•The diameter of the electrode canvary between 0.5 mm and 6.4 mm,and their length can range from 75 to610 mm .

• A number of tungsten alloys have been standardized by the InternationalOrganization for Standardization and the American Welding Society in ISO

6848 and AWS A5.12, respectively, for use in GTAW electrodes- refer table

• Pure tungsten electrodes (classified as WP or EWP) are general purposeand low cost electrodes. Cerium oxide (or ceria) as an alloying elementimproves arc stability and ease of starting while decreasing burn-off. Using

an alloy of lanthanum oxide (or lanthana) has a similar effect. Thorium oxide(or thoria) alloy electrodes were designed for DC applications and can

http://en.wikipedia.org/wiki/Lanthanum(III)_oxide


http://en.wikipedia.org/wiki/Thoria


http://en.wikipedia.org/wiki/Yttrium(III)_oxide




http://en.wikipedia.org/wiki/Zirconia












http://en.wikipedia.org/wiki/International_Organization_for_Standardization


http://en.wikipedia.org/w/index.php?title=American_Welding_Society&action=edit

http://en.wikipedia.org/wiki/Cerium


http://en.wikipedia.org/wiki/Lanthanum

http://en.wikipedia.org/wiki/Lanthanum%28III%29_oxide

http://en.wikipedia.org/wiki/Thorium



http://en.wikipedia.org/wiki/Thorium

http://en.wikipedia.org/wiki/Lanthanum%28III%29_oxide

http://en.wikipedia.org/wiki/Lanthanum


http://en.wikipedia.org/wiki/Cerium

http://en.wikipedia.org/w/index.php?title=American_Welding_Society&action=edit






(or thoria) alloy electrodes were designed for DC applications and canwithstand somewhat higher temperatures while providing many of thebenefits of other alloys.

• However, it is somewhat radioactive, and as a replacement, electrodes withlarger concentrations of lanthanum oxide can be used. Electrodescontaining zirconium oxide (or zirconia) increase the current capacity while

improving arc stability and starting and increasing electrode life.

• Electrode manufacturers may create alternative tungsten alloys withspecified metal additions, and these are designated with the classificationEWG under the AWS system.

• Filler metals are also used in nearly all applications of GTAW, the majorexception being the welding of thin materials. Filler metals are available withdifferent diameters and are made of a variety of materials. In most cases,the filler metal in the form of a rod is added to the weld pool manually, butsome applications call for an automatically fed filler metal, which is fed fromrolls.

shielding gases • Necessary in GTAW to protect the welding area from atmospheric

gases such as nitrogen and oxygen, which can cause fusiondefects, porosity, and weld metal embrittlement if they come incontact with the electrode, the arc, or the welding metal. The gas

also transfers heat from the tungsten electrode to the metal, and ithelps start and maintain a stable arc.


http://en.wikipedia.org/wiki/Radioactive_contamination

http://en.wikipedia.org/wiki/Zirconium



http://en.wikipedia.org/wiki/Zirconium

http://en.wikipedia.org/wiki/Radioactive_contamination











p• The selection of a shielding gas depends on several factors,

including the type of material being welded, joint design, and desiredfinal weld appearance.

• Argon is the most commonly used shielding gas for GTAW,

since it helps prevent defects due to a varying arc length. Whenused with alternating current, the use of argon results in highweld quality and good appearance.

• Another common shielding gas, helium, is most often used toincrease the weld penetration in a joint, to increase the weldingspeed, and to weld conductive metals like copper andaluminum.

• A significant disadvantage is the difficulty of striking an arcwith helium gas, and the decreased weld quality associatedwith a varying arc length.

Shielding Gas• Inert Gas - Argon , Helium

• Common Shielding Gas – Argon


http://en.wikipedia.org/wiki/Helium





http://en.wikipedia.org/wiki/Helium





Common Shielding Gas Argon

• When Helium Is Used – Called Heli – Arc Welding

• When Argon Is Used – Called Argon Arc Welding

• Inert Gas Prevents Contamination Of Molten Metal

• It Prevents Oxidation Of Tungsten Rod

• It Ionizes Air Gap and Stabilizes Arc

• It Cools Welding Torch & Tungsten Rod

Shielding Gas

• Argon - Purity 99.95%

• Impure Argon Results In Porosities




• Impure Argon Results In Porosities

• Purity Verified by Fusing BQ CS plate

• Leakage of Argon in Torch Results in

Porosity.

• Check Leakage by Closing the Ceramic CupWith Thump

Argon Gas Cylinder

• Light Blue In Colour

2




• Full Cylinder Pressure: 1800 psi ( 130 Kgs / Cm2 )

• Volume Of Argon In Full Cylinder: 7.3 M3

• Commercial Argon (99.99%) Cost: Rs 70/- Per M3

• High Purity Argon (99.999) Cost: Rs 87/- Per M3

Back Purging

Purging Gas Commercial Argon or

Nitrogen

• Applicable to Single

Sided full penetration




g p• Prevents oxidation of

root pass from opposite

side of weld

• Essential for high alloy

steels, nonferrous

metals and alloys

• Desirable For AllMaterial

Welding Torch

Root Pass

Purging Gas InPurging

Gas Out

Purgingchamber

Filler Wire

• Argon-helium mixtures are also frequently utilized inGTAW, since they can increase control of the heat inputwhile maintaining the benefits of using argon. Normally,the mixtures are made with primarily helium (often about75% or higher) and a balance of argon. These mixtures

increase the speed and quality of the AC welding ofaluminum and also make it easier to strike an arc




aluminum, and also make it easier to strike an arc.

• Argon-hydrogen, is used in the mechanized welding oflight gauge stainless steel, but because hydrogen cancause porosity, its uses are limited.

• Nitrogen can sometimes be added to argon to helpstabilize the austenite in austentitic stainless steels andincrease penetration when welding copper. Due toporosity problems in ferritic steels and limited benefits,

however, it is not a popular shielding gas additive.

Materials • Most commonly used to weld stainless steel

and nonferrous materials, such as aluminumand magnesium, but it can be applied to

nearly all metals, with notable exceptionsbeing lead and zinc



http://en.wikipedia.org/wiki/Austenite

http://en.wikipedia.org/wiki/Austenite



http://en.wikipedia.org/wiki/Lead

http://en.wikipedia.org/wiki/Zinc






y pbeing lead and zinc.

• Its applications involving carbon steels arelimited not because of process restrictions,

but because of the existence of moreeconomical steel welding techniques, suchas gas metal arc welding and shielded metalarc welding.

• GTAW can be performed in a variety of other-

than-flat positions, depending on the skill ofthe welder and the materials being welded.











http://en.wikipedia.org/wiki/Image:TIG_weld_etch_zone_closeup.jpg

http://en.wikipedia.org/wiki/Image:TIG_Weld_low_magnification.jpg




A TIG weld showing anaccentuated AC etched zone

Closeup view of an

aluminium TIG weld AC etch zone

• Aluminum and magnesium are most often welded usingalternating current, but the use of direct current is alsopossible, depending on the properties desired. Beforewelding, the work area should be cleaned and may bepreheated to 175-200 °C for aluminum or to a maximumof 150 °C for thick magnesium workpieces to improve

penetration and increase travel speed.AC c rrent can pro ide a self cleaning effect remo ing

http://en.wikipedia.org/wiki/Image:TIG_weld_etch_zone_closeup.jpg

http://en.wikipedia.org/wiki/Image:TIG_Weld_low_magnification.jpg












• AC current can provide a self-cleaning effect, removingthe thin, refractory aluminium oxide (sapphire) layer thatforms on aluminium metal within minutes of exposure toair. This oxide layer must be removed for welding to

occur. When alternating current is used, pure tungstenelectrodes or zirconiated tungsten electrodes arepreferred over thoriated electrodes, as the latter aremore likely to "spit" electrode particles across thewelding arc into the weld.

• Blunt electrode tips are preferred, and pure argonshielding gas should be employed for thin workpieces.Introducing helium allows for greater penetration inthicker workpieces, but can make arc starting difficult.

• Direct current of either polarity, positive or negative,can be used to weld aluminum and magnesium aswell.

• DCEN allows for high penetration, and is mostcommonly used on joints with butting surfaces, such

as square groove joints. Short arc length (generallyless than 2 mm or 0.07 in) gives the best results,

http://en.wikipedia.org/wiki/Sapphire

http://en.wikipedia.org/wiki/Sapphire




making the process better suited for automaticoperation than manual operation. Shielding gaseswith high helium contents are most commonly usedwith DCEN, and thoriated electrodes are suitable.

• DCEP is used primarily for shallow welds, especiallythose with a joint thickness of less than 1.6 mm.While still important, cleaning is less essential forDCEP than DCEN, since the electron flow from theworkpiece to the electrode helps maintain a clean

weld. A large, thoriated tungsten electrode iscommonly used, along with a pure argon shieldinggas.

Steels• For GTA welding of carbon and stainless steels, theselection of a filler material is important to preventexcessive porosity. Oxides on the filler material andworkpieces must be removed before welding to prevent

contamination, and immediately prior to welding, alcoholor acetone should be used to clean the surface.

http://en.wikipedia.org/wiki/Carbon_steel







• Preheating is generally not necessary for mild steels lessthan one inch thick, but low alloy steels may requirepreheating to slow the cooling process and prevent the

formation of martensite in the heat-affected zone.• Tool steels should also be preheated to prevent crackingin the heat-affected zone. Austenitic stainless steels donot require preheating, but martensitic and ferriticchromium stainless steels do. A DCEN power source isnormally used, and thoriated electrodes, tapered to asharp point, are recommended. Pure argon is used forthin workpieces, but helium can be introduced asthickness increases.

Dissimilar metals

• Welding dissimilar metals often introduces new difficulties toGTA welding, because most materials do not easily fuse toform a strong bond. Welds of dissimilar materials havenumerous applications in manufacturing, repair work, and the

prevention of corrosion and oxidation. In some joints, acompatible filler metal is chosen to help form the bond, and

http://en.wikipedia.org/wiki/Martensite

http://en.wikipedia.org/wiki/Heat-affected_zone

http://en.wikipedia.org/wiki/Tool_steel

http://en.wikipedia.org/wiki/Tool_steel





http://en.wikipedia.org/wiki/Corrosion

http://en.wikipedia.org/wiki/Oxidation

http://en.wikipedia.org/wiki/Oxidation

http://en.wikipedia.org/wiki/Corrosion




p pthis filler metal can be the same as one of the base materials(eg:, using a stainless steel filler metal stainless steel andcarbon steel as base materials), or a different metal (such asthe use of a nickel filler metal for joining steel and cast iron).Very different materials may be coated or "buttered" with amaterial compatible with a particular filler metal, and thenwelded. In addition, GTAW can be used in cladding oroverlaying dissimilar materials.

• When welding dissimilar metals, the joint must have anaccurate fit, with proper gap dimensions and bevel angles. Careshould be taken to avoid melting excessive base material.

Pulsed current is particularly useful for these applications, as ithelps limit the heat input. The filler metal should be addedquickly, and a large weld pool should be avoided to preventdilution of the base materials.

Process variationsPulsed-current

• In the pulsed-current mode, the welding current rapidlyalternates between two levels.

• The higher current state is known as the pulse current, while the lower current level is called the backgroundcurrent


http://en.wikipedia.org/wiki/Cast_iron

http://en.wikipedia.org/wiki/Cladding

http://en.wikipedia.org/wiki/Overlaying

http://en.wikipedia.org/wiki/Overlaying

http://en.wikipedia.org/wiki/Cladding






current.

• During the period of pulse current, the weld area isheated and fusion occurs. Upon dropping to thebackground current, the weld area is allowed to cool and

solidify.• Pulsed-current GTAW has a number of advantages,

including lower heat input and consequently a reductionin distortion and warpage in thin workpieces. In addition,it allows for greater control of the weld pool, and can

increase weld penetration, welding speed, and quality. Asimilar method, manual programmed GTAW, allows theoperator to program a specific rate and magnitude ofcurrent variations, making it useful for specializedapplications.

Dabber

• The Dabber variation is used to precisely placeweld metal on thin edges. The automatic

process replicates the motions of manualwelding by feeding a cold filler wire into the weld




g y garea and dabbing (or oscillating) it into thewelding arc. It can be used in conjunction with

pulsed current, and is used to weld a variety ofalloys, including titanium, nickel, and tool steels.Common applications include rebuilding seals in

jet engines and building up saw blades, milling

cutters, drill bits, and mower blades

Heat-affected zone

http://en.wikipedia.org/wiki/Jet_engines

http://en.wikipedia.org/wiki/Milling_cutter


http://en.wikipedia.org/wiki/Drill_bit

http://en.wikipedia.org/wiki/Drill_bit



http://en.wikipedia.org/wiki/Jet_engines

http://en.wikipedia.org/wiki/Image:Welded_butt_joint_x-section.png




The cross-section of a welded butt joint, with thedarkest gray representing the weld or fusion zone,

the medium gray the heat affected zone, and

the lightest gray the base material.

• The heat-affected zone (HAZ) is the area of basematerial, either a metal or a thermoplastic, which hashad its microstructure and properties altered by welding.The heat from the welding process and subsequent re-cooling causes this change in the area surrounding theweld. The extent and magnitude of property changedepends primarily on the base material, the weld fillermetal and the amount and concentration of heat input

http://en.wikipedia.org/wiki/Image:Welded_butt_joint_x-section.png


http://en.wikipedia.org/wiki/Thermoplastic



http://en.wikipedia.org/wiki/Thermoplastic





metal, and the amount and concentration of heat inputby the welding process.

• The thermal diffusivity of the base material plays a largerole – if the diffusivity is high, the material cooling rate is

high and the HAZ is relatively small. Alternatively, a lowdiffusivity leads to slower cooling and a larger HAZ. Theamount of heat inputted by the welding process plays animportant role as well, as processes like oxyfuel welding use high heat input and increase the size of the HAZ.

Processes like laser beam welding give a highlyconcentrated, limited amount of heat, resulting in a smallHAZ. Arc welding falls between these two extremes, withthe individual processes varying somewhat in heat input

• To calculate the heat input for arc weldingprocedures, the formula used is:

http://en.wikipedia.org/wiki/Thermal_diffusivity

http://en.wikipedia.org/wiki/Oxyfuel_welding

http://en.wikipedia.org/wiki/Laser_beam_welding

http://en.wikipedia.org/wiki/Laser_beam_welding

http://en.wikipedia.org/wiki/Oxyfuel_welding

http://en.wikipedia.org/wiki/Thermal_diffusivity




where Q = heat input (kJ /mm), V = voltage (V), I =current (A), and S = welding speed (mm/min). The

efficiency is dependent on the welding process used,

with shielded metal arc welding having a value of

0.75, gas metal arc welding and submerged arcwelding, 0.9, and gas tungsten arc welding, 0.8.

Types Of GTAW Power Source

• Inverter- DC

• Thyrister – DC

http://en.wikipedia.org/wiki/Kilojoule

http://en.wikipedia.org/wiki/Millimetre

http://en.wikipedia.org/wiki/Volt

http://en.wikipedia.org/wiki/Amp



http://en.wikipedia.org/wiki/Submerged_arc_welding








http://en.wikipedia.org/wiki/Amp

http://en.wikipedia.org/wiki/Volt

http://en.wikipedia.org/wiki/Millimetre

http://en.wikipedia.org/wiki/Kilojoule




y



• Transformer – AC (For Aluminium Welding Only)

Power Source

• Provides Electric Energy – Arc – Heat

D i Ch i i




• Drooping Characteristic

• OCV – Appx. 90V,

• Current Range 40 A to 300 A ( Capacity Of M/s)

• Arc Voltage 18V to 26V

Characteristic Of GTAW

Power Source

Drooping Constant Current




A

Vertical

Curve

V1

V2

A1 A2

Drooping – Constant Current

V

High Frequency Unit

• Provides High Voltage Electric Energy With Very

high Frequency – 10000 Cycles / Sec.




• Initiates low energy Arc / Spark & Ionize Air Gap.

• Electrically charges Air Gap For welding Currentto Jump Across the Tungsten Tip & BM to FormAn Arc.

• HF Gets Cut Off, Once Welding Arc Struck.



Pedal Switch

S it h t

When Pedal Pressed

• Solenoid valve opens, Argon gas flows

• High Frequency current jumps from

tungsten rod generating sparks• Welding current flows generating an




Switches system

on And off in sequence

• Welding current flows generating anarc across tungsten rod and work.

• High frequency gets cut off from the

system & welding continues.When Pedal Released

1 Current gets cut off, Arc extinguishes

2 Gas flow remains for few moreseconds before it stops.

Argon Gas Cylinder- Pressure Regulator +

Flow Meter

• Cylinder Stores Argon At

Hi h P




High Pressure

• Regulator Regulates

Cylinder Pressure to

Working Pressure

• Flow Meter Controls

Flow Rate

Argon Cylinder

Flow Meter

Pressure Regulator

Flow Regulator

Pressure gauges

Cylinder Valve

Connection To Torch

Tools For GTAW

• Head Screen




• Hand gloves

• Chipping Hammer

• Wire Brush

• Spanner Set

Filler Wire

• Added Separately to the weld pool.

C ibl b l




• Compatible to base metal

• Used in cut length for manual welding.

• Used from layer wound spool for automaticwelding.

• Sizes :- 0.8, 1, 1.2, 1.6, 2, 2.4 & 3 mm

ASME Classification Of Filler Wire

SS Filler Wire:

SFA-5.9, ER 308, 308L, 316, 316L, 347, 309




LAS Filler Wire:

SFA 5.28, ER 70S A1, ER 80S B2, ER90S D2,

ER 80S Ni2

CS Filler Wire:

SFA- 5.18 , ER 70S2C = 0.07%, Mn = 0.9% – 1.4%, Si = 0.4 – 0.7%, P = 0.025%, S = 0.035%

Dos & Don'ts In GTAW

• Always Connect

Electrode – Ve

• Keep Always Flow

• Don’t Strike Arc With

Electrode + Ve

• Don’t strike Arc Without

Dos Don’ts




Meter Vertical

• Check & Confirm

Argon Purity

• Clean Groove & Filler

wire With Acetone

• Grind Tungsten Tip toPoint

Argon Flow

• Don’t Strike Arc By

touching Tungsten Rod

• Don’t Touch Weld Pool

With Tungsten Rod

• Don’t Lift and break Arc



Dos & Don'ts In GTAW

• Provide Back Purging For

Single Sided FullPenetration Welds

• Don’t Weld Single Sided

Full Penetration WeldsWithout Back Purging

Dos Don’ts




Penetration Welds

• Use N2 or Argon as Back

Purging Gas For CS &

LAS

• Use Argon As Back

Purging Gas For SS &

Non Ferrous Alloys

Without Back Purging

• Don’t Use N2 As Back

Purging Gas For Non

Ferrous Alloys

• Don’t Empty Ag Cylinders

Fully.

Defects In GTAW

1. Cracks 2. Lack Of Fusion

i d




3. Porosity 4. Undercut

5.Lack Of Penetration 6. Excess Penetration

7.Overlap 8. Suck Back

9. Under Flush 10. Burn Through

11. Tungsten Inclusion 11.Stray Arcing

Crack

Cause Remedy

1) Wrong Consumable2) Wrong Procedure

1) Use Right Filler Wire2) Qualify Procedure




2) Wrong Procedure

3) Improper Preheat

4) Inadequate ThicknessIn Root Pass

2) Qualify Procedure

3) Preheat Uniformly

4) Add More Filler Wirein root Pass

crack

Lack Of Fusion

Cause Remedy

1) Inadequate Current 1) Use Right Current




) q

2) Wrong Torch angle

3) Improper bead placement

) g

2) Train /Qualify welder

3) Train/Qualify Welder

Lack Of Fusion

PorosityCause Remedy

1) Impure Argon Gas

2) Argon Leak Within Torch

3) Defective Filler Wire

1) Replace Argon Cylinder

2) Replace Leaking Torch

3) Replace Filler Wire




4) Wet surface of BM

5) Rusted / Pitted Filler wire

6) Improper Flow Of Argon

4) Clean & Warm BM

5) Clean Filler Wire

6) Provide Gas lens

Porosity . .

Undercut

Cause Remedy1) Excess Current 1) Reduce the Current




)

2) Excess Voltage

3) Improper Torch angle

)

2) Reduce Arc length

3) Train & Qualify the Welder

Under cut

Lack Of Penetration*

Cause Remedy

1) Excess Root Face

2) Inadequate Root opening3) Over size Filler Wire

1) Reduce Root Face

2) Increase Root Opening3) Reduce Filler Wire size




3) Over size Filler Wire

4) Wrong Direction of Arc

5) Improper bead placement6) Improper weaving technique

3) Reduce Filler Wire size

4) Train / Qualify Welder

5) Train / Qualify Welder6) Train & Qualify Welder

LOP

* Applicable to SSFPW

Excess Penetration*Cause Remedy

1)Excess root opening

2) Excess Current

1) Reduce root gap

2) Reduce Current




3) Inadequate root face

4) Excess Weaving

5) Wrong Direction Of Arc

3) Increase Root face

4) Train Welder

5) Train Welder

Excess Penetration


Overlap

Cause Remedy

1) Wrong Direction Of Arc 1) Train & Qualify Welder




2) Inadequate Current

3) Excess Filler Wire

2) Increase Current

3) Reduce Filler Metal

Overlap

Suck Back *

Cause Remedy

1) Excess weaving in root 1) Reduce weaving




2) Excess Current

3) Inadequate root face

4) Wrong Electrode angle

2) Reduce Current

3) Increase root face


Suck Back

* Applicable to SSFPW in 4G, 3G & 2G

Under flushCause Remedy

1) Inadequate weld beads in

final layer

2) Inadequate understanding on

ld i f t

1) Weld some more beads

in final layer

2) Train / Qualify welder




weld reinforcement

3) Wrong selection of filler wire

size


Under flush

Burn through*Cause Remedy

1) Excess Current

2) Excess Root opening3) Inadequate Root face

1) Reduce the Current

2) Reduce root opening3) Increase root face




) q

4) Improper weaving

)


Burn trough

*Applicable to root pass

Tungsten InclusionCause Remedy

1) Ineffective HF

2) Improper Starting of Arc

1) Rectify HF Unit

2) Never Touch Weld




3) Tungsten Tip Comes in

Contact With Weld

With Tungsten Rod


Tungsten Inclusion

Stray Arcing

Cause Remedy

1) HF Not In Operation2) Inadequate Skill of Welder

1) Rectify HF Unit2) Train the Welder




2) Inadequate Skill of Welder 2) Train the Welder

Arc Strikes



What Is GMAW ?• A Fusion Welding Process – Semi Automatic

• Arc Between Consumable Electrode &Work

• Arc Generated by Electric Energy From a Rectifier



• Arc Generated by Electric Energy From a Rectifier/ Thyrester / Inverter

• Filler Metal As Electrode Continuously fed FromLayer Wound Spool.

• Filler Wire Driven to Arc By Wire Feeder throughWelding Torch

• Arc & Molten Pool Shielded by Inert Gas throughTorch / Nozzle

Gas Metal Arc Welding

• MIG – Shielding Gas Ar / Ar + O2 / Ar + Co2

MAG Shi ldi G C



• MAG – Shielding Gas Co2

• FCAW – Shielding Gas Co2 With Flux cored

Wire

Note:- Addition of 1 – 5% of O2 or 5 – 10% of Co2 in Ar.

increases wetting action of molten metal

Power Source For MIG / MAG

• Inverter- DC



• Thyrister – DC



Characteristic Of GMAW PowerSource

Constant V / Linear Characteristic

V



Appx. Horizontal

Curve

V1V2

A1 A2A

V

Current & Polarity

DC- Electrode +Ve

Stable Arc

S h l f



Smooth Metal Transfer

Relatively Low Spatter

Good Weld Bead Characteristics

DC- Electrode – ve, Seldom Used

AC- Commercially Not In use

Accessories Of GMAW

• Power Source• Wire Feed Unit



• Shielding Gas Cylinder, Pressure gauges/

Regulator, Flow meter (Heater For Co2 )• Welding Torch

• Water Cooling System (For Water cooled Torch)


Tools For GMAW• Head Screen With DIN 13 / 14 Dark Glass

• Hand Wire Brush / Grinder With Wire Wheel

• Cutting Pliers



Cutting Pliers

• Hand Gloves

• Chipping Hammer / Chisel & hammer• Spanner Set

• Cylinder Key

• Anti-spatter Spray


GMAW Torch

Torch HandleShielding Gas

On / Off Switch



Torch HandleSpring Conduit

Job

Arc

Gas Cup

Filler Wire - Electrode Nozzle Tip

Equipment & AccessoriesFlow Meter

Pressure Regulator

Solenoid

Shielding Gas Heater

(Only ForC )Switch



+ –

Wire Inside Spring Lining Welding Torch Wire Feeder

Shielding GasCylinder

Argon / Co2 Shielding

Power Source

With Inductance

Work

Arc –

Valve

Copper Cup

WireSpool

Electrode /Wire

Co2)

Contact Tip

Switch

Torch With Cable Max. 3Mtr



Dr. N. RAMACHANDRAN, NITC 340• A TYPICAL GMAW WELDING SET UP

GAS METAL ARC WELDING (GMAW)ALMOST REPLACING SMAW, FASTER, INTRODUCED IN 1940’S,

DCRP GENERALLY EMPLOYED, CONTINUOUS WIRE FEEDING

MODES OF METAL TRANSFER

1

SPRAY

2

SHORT

CIRCUIT

3

GLOBULAR

4

BURIED ARC

5

PULSED

ARC

HIGH VERY LOW UNIQUE IN PULSING




VOLTAGE

HIGH

AMPERAGE

(WIRE FEED)

VOLTAGE

MODERATE

WIRE FEED

BETWEEN 1&2

Q

GMAW,

HIGHER WIRE

FEED

BETWEEN

MODES

DROPLETS-

DEEP Penet.

FOR THICK

COOLEST

MODE,

LEAST

Penetration.

FOR CARBON

STEELS, 6 TO

12 MM

HIGH SPPED,

LOW SPATTER,

DEEP Penet.,

FOR MS AND SS

NO GUN

OSCILLATI

ON

ARGON ST.

(FOR

NARROW)

75 % Ar +

25% CO2

90%Ar + 7.5%

CO2 +2.5% He

FOR

THICK TO

THIN,DISSIMILAR



Function Of Shielding Gas InGMAW

• Prevents Air contamination of weld Pool

• Prevents Contamination During Metal



• Prevents Contamination During MetalTransfer

• Increases fluidity of molten metal• Minimizes the spatter generation

• Helps in even & uniform bead finish

Gas Metal Arc WeldingEffects of Shielding gas

1. Filler Metal Deposition Rate and Efficiency

2. Spatter Control and Post weld Cleaning




3. Bead Profile and Overwelding

4. Bead Penetration, Potential for Burn-through

5. Out-of-position Weldability

6. Welding Fume Generation Rates

7. Weld Metal Mechanical Properties

GASES• PUROPOSE-

1.TO SHIELD MOLTEN PUDDLE FROM CONTAMINATION

2.CREATE A SMOOTH ELECTRICAL CONDUCTION

PATH FOR ELECTRONS IN ARC

• SOME GASES (ARGON)MAKE SMOOTH PATH, BUT SOMERESISTS (CO2) PATH.

STRAIGHT ARGON FOR NARROW BEADS




• STRAIGHT ARGON FOR NARROW BEADS

• 98% Ar+ 2 OXYGEN FOR SPRAY,

• He FOR COPPER, THICK Al (WITH Ar).

• 75 % Ar + 25% CO2 FOR SHORT CIRCUIT.,

• STRAIGHT CO2 ECONOMICAL, BUT SPATTERING.

• 90%Ar + 7.5% CO2 +2.5% He FOR BURIED ARC, SS.

• 90% Ar + 10% He FOR AUTOMATIC V, WIRE FEED SYSTEMS

• A CONSTANT VOLTAGE POWER SOURCE USED.

Shielding Gases For GMAW

• MIG: Argon Or Helium

For SS, CS, LAS & Non-ferrous Mt & Al• MIG: Ar + 1 to 2 % O2, Wire With Add. Mn & Si



For SS, CS, LAS & Non-ferrous Mt & Al

• MIG: Ar + 5 to 20 % Co2 Wire With Add. Mn & Si

For SS, CS, LAS & Non-ferrous Mt & Al

• MAG: Co2 With Solid Wire

For CS & LAS

• FCAW: Co2 With Flux Cored Wire

For CS, LAS & SS Overlay

Different types of shielding gases

Pure Gases

• Argon

• Helium




• Carbon Dioxide

Argon.

Argon is a monatomic (single-atom) gas commonly used for

GTAW on all materials and GMAW on nonferrous metals.

Argon is chemically inert, making it suitable for welding on

reactive or refractory metals.

Low thermal conductivity and ionization potential, properties thatresult in a low transfer of heat to the outer areas of the arc.

Helium.




• Helium also is a monatomic, inert gas, most commonly used for

GTAW on nonferrous materials.

• In contrast to argon, helium has a high conductivity andionization potential, which gives the opposite effects.

• Helium provides a wide profile ,good wetting on the edges of the

bead, and higher heat input than pure argon.

• The high ionization potential can create difficulty in arc starting

unless high-frequency or capacitive arc starting is used for GTAW

Carbon dioxide

CO2 usually is used for GMAW short-circuit transfer

and FCAW.

The CO2 will disassociate into CO and O2 at thetemperatures encountered in the arc. This creates the

potential for oxidizing of the base metal




Recombination of the CO/O2 gives wide penetration

profile at the surface of the weld, while the low

ionization potential and thermal conductivity createa hot area at the center of the arc column.

For GMAW applications, pure CO2 is unable to produce

spray transfer, and it promotes globular transfer, which

causes spatter.




The traditional pure argon

penetration profile is deep and narrow.

The helium penetration

profile is wider than argon’s

The CO2 penetration profile is

marked by good width and depth

Other Gases Used in Mixtures

•Oxygen

• Oxygen creates a very wide and shallow penetration profile,

with high heat input at the surface of the work.

• Spray transfer is facilitated, as well as wetting at the toe of the

weld.

• Oxygen/argon mixes exhibit a characteristic "nailhead" penetration

profile with GMAW carbon steel Oxygen also is used in trimixes




profile with GMAW carbon steel, Oxygen also is used in trimixes

with CO2 and argon,

•Hydrogen• Active shielding gas -at concentrations of less than 10 %

• Hydrogen is primarily used with austenitic stainless steels

• Hydrogen is not suitable for ferritic or martensitic steels because

of cracking issues.

• Hydrogen also may be used in higher percentages (30 percent to

40 percent) in plasma cutting operations on stainless steel to increase

capacity and reduce slag.

Gas Mixtures




Different combinations of welding processes and materials require different combinations ofwelding gases.

The graphic on the left shows good

shielding gas coverage. The graphicon the right shows what happens

when air is allowed to seep into

and contaminate the gas.

ARGON/CO2

•CO2 content varies from 5 percent to 25 percent.

•Used for spray transfer on heavy materials or when low heat

input and shallow penetration are desired for thin materials.

•High CO2 content promotes short-circuit transfer and can provide

additional cleaning action and deep penetration in heavy materials




ARGON/O2

•Oxygen percentage usually is between 2 and 5.

• Typically used in spray transfer on fairly clean materials

ARGON/O2 /CO2

•Work well in both spray transfer and short-circuit mode and may

be used on many material thickness.

•Oxygen tends to promote spray transfer at low voltages, while theCO2 aids penetration.




The argon/CO2 penetration profile

can be adjusted by the amount of

CO2 contained in the gas mixture

The argon/O2 penetration profile is

deeper and not as wide as that of the

argon/CO2 profile.

+ POINTS OF GMAW• HIGH WELDING SPEED

• NO NEED TO CHANGE ELECTRODES (ONLY WIRE SPOOLIN GMAW)

• HAZ SMALL

• VERY LITTLE SMOKE AND VERY LIGHT SiO2

SLAG(CALLED GLASS SLAG)

• LEAST DISTORTION




• LEAST DISTORTION

• EASE OF OPERATION (QUICK LEARNING)

• GUN MANIPULATION EASIER

• MOST FLEXIBLE PROCESS- VERSATILE

• VERY FEW MACHINE ADJUSTMENTS FOR THICK TOTHIN CHANGE

• MS, MCS, TOOL STEEL GRADES, SS, COPPER, Al, MgWELDED

• FCAW, SAW, ESW- OTER FORMS OF GMAW

ABOUT THE POWER SOURCE

• DCRP, DCSP, ACHF USED

• ELECTRODES OF 0.25 mm TO 6.4 mm FOR

DIFFERENT APPLICATIONS

• ELECTRODES CODED, WITH COLOR STRIPS




,

• BEST FOR ALUMINIUM, SINCE OXIDE FILM BREAKS

BY PENETRATION

Frequent cleaning and shaping of electrode tip to be done

WELDINGTECHNIQUE

GMAW

SHIELDING GAS Argon (95%) +

O2(5%)

PLATE THICKNESS

(mm)

7

TRAILING SHIELD Argon (99.99%)

GROOVE GEOMETRY SINGLE ‘V’ 45

ANGLE

o 45

1 . 0 mm

2 mm




ANGLE

ROOT GAP (mm) 2

ROOT FACE (mm) 1

CURRENT (A) 300-310

VOLTAGE (V) 30-31

SPEED (mm/sec) 5.8

HEAT INPUT (KJ/mm) 1.5-1.6

NO. OF PASSES 1




Welding Hull of Ships




For increasing productivity in Fabrication by

GMAW Process different shieldinggases used

Typical Welding Parameters used

Gases Used Code Current

(Amp)

Voltage

(Volt)

Welding

Speed

(Meter/Min)

Heat Input

(KJ/mm)

9 %A %O A 200 210 29 0 3 4 0 9

Gas Flow Rate : 18-20 lpm

Electrode Stick Out : 15mm

Polarity : DCEP




95%Ar-5%O2 A 200-210 29 0.374 0.95

B 250-260 30 0.375 1.22

C 300-310 30 0.37 1.580%Ar-20%CO2 D 200-210 29 0.374 1.0

E 250-260 29 0.374 1.2

F 300-310 30 0.375 1.5

Pure CO2 G 200-220 30 0.374 1.01

H 250-260 30 0.375 1.28

I 300-320 31 0.375 1.6

Sample code Heat Input

(KJ/mm)

Yield

Strehgth(N/mm2)

% Elongation Avg. Impact

Toughness (J)

NG-A-5O2 1.0 604 23 48

Experimental results of a typical study:




NG-B-5O2 1.22 666 21 38

NG-C-5O2 1.5 775 20 33

NG-D-20CO2 1.0 716 15 30

NG-E-20CO2 1.2 627 18 33

NG-F-20CO2 1.5 663 14 14

Weld Bead Morphology

95%Ar-5%O2

Deep

Penetration *

80%Ar

Bead in V Groove Weld Bead on Plate Weld




80%Ar-

20%CO2

PureCO2

Narrow Penetration

Bead in V Groove Weld Bead on Plate Weld

*When used for single pass welding of plates of thickness 6-7 mm

5

6

7

( m m )

80 Ar / 20 CO2

Pure CO2

95 Ar / 5 O2

Effect of shielding gas on weld penetration




2

3

4

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

Heat Input (KJ/mm)

P e n e t r a t i o n (

80

85

90

95

100

f f i c i e n c y ( % )

80 Ar / 20 CO2

Pure CO2

95 Ar / 5 O2

Effect of shielding gas on deposition efficiency




60

65

70

75

80

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

Heat Input (KJ/mm)

D

e p o s i t i o n E f

6

7

8

9

10

R a t e ( K g / h r )

80 Ar / 20 CO2

Pure CO2

95 Ar / 5 O2

Effect of shielding gas on Deposition rate




2

3

4

5

6

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

Heat Input (KJ/mm)

D

e p o s i t i o n R

Types Of Wire Feeding InGMAW

• Push Type – Wire fed in to The torch by Pushing through Flexible

Conduit From A Remote Spool



Conduit From A Remote Spool

• Pull Type

– Feed Rollers Mounted on The Torch Handle Pulls theWire From A Remote spool

• Self Contained

– Wire Feeder & The Spool On the Torch

ASME Classification For CSGMAW Wire

• SFA 5.18 : - CS Solid Wire

ER 70 S – 2, ER 70 S – 3

ER 70 S – 6, ER 70 S – 7



• SFA 5.20 :- CS Flux Cored WireE 71 T-1, E 71 T-2 ( Co2 Gas )

E 71 T-1M, E 71 T-2M ( Ar + Co2 Mix)

GMAW CS Wire

• Generally Copper Coated

– Prevents Oxidation / rusting in Storage – Promotes Electric Conductivity in Arcing

• Available In Solid & Flux Cored



• Available In Solid & Flux Cored

– Size in mm 0.8, 1, 1.2, 1.6, 2, 2.4, 3

• Manganese & Silicon ( Mn 1 – 2 %, Si Max 1%)

– Act As Deoxidizing Agents

– Eliminate Porosity

– Increase Wetting Of Molten Pool

Metal Transfer In MIG

• Short-Circuiting / Dip Transfer



• Globular Transfer

• Spray Transfer

Metal Transfer In MIGCS Solid Wire 1.2 mm Φ

Above230A

24 – 35 V

120 to 250A

16 – 24 V

Up to 120A

14 – 22V



Dip/Short Circuiting Globular Spray

Co2 or Ar Co2 or Ar Only Ar / Ar+O2

Short-Circuiting / Dip Transfer• Wire In Contact With Molten Pool 20 to 200 times per

Second

• Operates in Low Amps & Volts – Less Deposition

• Best Suitable for Out of Position Welding



• Suitable for Welding Thin Sheets

• Relatively Large opening of Root Can be Welded• Less Distortion

• Best Suitable for Tacking in Set up

• Prone to Get Lack of Fusion in Between Beads

Globular Transfer

• Metal transferred in droplets of Size grater thanwire diameter

O t i M d t A & V lt B tt



• Operates in Moderate Amps & Volts – Better

Deposition• Common in Co2 Flux Cored and Solid Wire

• Suitable for General purpose Welding

Spray Transfer

• Metal transferred in multiples of small droplets

• 100 to 1000 Droplets per Second• Metal Spray Axially Directed

• Electrode Tip Remains pointed



Electrode Tip Remains pointed

• Applicable Only With Inert Gas Shielding –

Not With Co2

• Operates in Higher Amps & Volts – HigherDeposition Rate

• Not Suitable for Welding in Out of Position.

• Suitable for Welding Deep Grooves

Pulsed Spray Welding

• Power Source Provides Two differentCurrent Levels“Background” and “Peak”atregular interval



regular interval

• “Background” & “Peak” are above and below the Average Current

• Best Suitable for Full Penetration OpenRoot Pass Welding

• Good Control on Bead Shape and Finish

Synergic Pulse GMAW

• Parameters of Pulsed Current (Frequency,Amplitude, Duration, Background Current)Related to Wire feed Rate



• One Droplet detaches with each pulse

• An Electronic Control unit synchronizes wire feedRate with Pulse Parameters

• Best Suitable for Most Critical Full PenetrationOpen Root Pass Welding

• Good Control on Open Root penetration, BeadShape and Finish

GMAW Process Variables• Current

• Voltage• Travel Speed



• Stick Out / Electrode Extension

• Electrode Inclination• Electrode Size

• Shielding Gas & Flow Rate

• Welding Position

Parameter For 1.2 ф FC Wire

• Current – 200 to 240 A

• Voltage – 22-24

• Travel Speed 150 to 250 mm / min



Travel Speed 150 to 250 mm / min

• Stick Out / Electrode Extension – 15 to 20 mm

• Electrode Inclination – Back Hand Technique

• Shielding Gas – Co2, 12 L/Min

Parameter For 1.2 ф Solid Wire

• Current – 180 to 220 A

• Voltage – 20-22

• Travel Speed 150 to 200 mm / min



Travel Speed 150 to 200 mm / min

• Stick Out / Electrode Extension – 10 to 20 mm

• Electrode Inclination – Back Hand Technique

• Shielding Gas – Co2 – 12 L/Min

Results In Change Of Parameters• Increase In Current

– More deposition, More Penetration, More BM Fusion

• Increase In Voltage – More Weld Bead Width, Less Penetration, Less

Reinforcement, Excess Spatter



• Increase In Travel Speed

– Decrease in Penetration, Decrease in Bead Width,• Decrease In Gas Flow rate

– Results In porosity

• Long Stick Out / Electrode Extension

– Excess Weld Deposit With Less Arc intensity, Poor BeadFinish, Shallow Penetration

Common Defects In GMAW

1. Porosity 2. Spatters3. Lack Of Fusion 4. Under Cut

5 Over Lap 6 Slag



5. Over Lap 6. Slag

7. Crack 8. Lack Of Penetration9. Burn Through 10. Convex Bead

11. Unstable Arc 12. Wire Stubbing

Porosity

Cause Remedy1) Less Mn & Si In Wire

2) Rusted / Unclean BM / Groove

1) Use High Mn & Si Wire

2) Clean & warm the BM



)

3) Rusted wire

4) Inadequate Shielding Gas

)

3) Replace the Wire

4) Check & Correct Flow Rate

Porosity . .

SpattersCause Remedy

1) Low Voltage

2) Inadequate Inductance

3) Rusted BM surface

4) Rusted Core wire

1) Increase Voltage

2) Increase Inductance

3) Clean BM surface

4) Replace By Rust Free wire



5) Quality Of Gas 5) Change Over To Ar + Co2

Spatters

• • •

Lack Of FusionCause Remedy


2) Inadequate Voltage

3) Wrong Polarity

1) Use Right Current

2) Use Right Voltage

3) Connect Ele. + Ve



4) Slow Travel Speed

5) Excessive Oxide On Joint

4) Increase Travel speed

5) Clean Weld Joint

Lack Of Fusion

Undercut

Cause Remedy

1) Excess Voltage

2) Excess Current

1) Reduce Voltage

2) Reduce Current



)

3) Improper Torch angle

4) Excess Travel Speed

)

3) Train & Qualify the Welder

4) Reduce Travel Speed

Under cut

Overlap

Cause Remedy

1) Too Long Stick Out 1) Reduce Stick Out



2) Inadequate Voltage 2) Increase the Voltage

Overlap

SlagCause Remedy

1) Inadequate Cleaning



1) Clean each bead

2) Use Right Current




4) Improper bead placement 4) Train / Qualify Welder

Slag

Crack

Cause Remedy

1) Incorrect Wire Chemistry 2) Too Small Weld Bead

3) Improper Preheat

1) Use Right Wire

2) Increase wire Feed

3) Preheat Uniformly



4) Excessive Restrain 4) Post heating or ISR

crack

Lack Of Penetration*

Cause Remedy

1) Too Narrow Groove Angle

2) Inadequate Root opening

3) Too Low Welding current


1) Widen The Groove

2) Increase Root Opening

3) Increase Current




) g g

5) Puddle Roll In Front Of Arc

6) Long Stick Out

) Q y

5) Correct Torch Angle

6) Reduce Stick Out

LOP


Burn through*

Cause Remedy

1) Excess Current

2) Excess Root opening

3) Inadequate Root face

4) Too Low Travel Speed

1) Reduce the Current

2) Reduce root opening

3) Increase root face

4) Increase Speed



) p

5) Quality Of Gas

) p

5) Use Ar + Co2

Burn trough*Applicable to root pass

Convex Bead FinishCause Remedy

1) Low Current

2) Low Voltage

3) Low Travel Speed

4) L I d

1) Increase Current

2) Increase Voltage

3) Increase Travel Speed

4) I I d



4) Low Inductance

5) Too Narrow Groove

4) Increase Inductance

5) Increase Groove Width

Uneven bead finish

Unstable arc

Cause Remedy1) Improper Wire Feed

2) Improper Gas Flow

1) Check Wire Feeder

2) Check Flow Meter



2) Improper Gas Flow

3) Twisted Torch Conduit

2) Check Flow Meter

3) Straighten Torch Cab

Wire Stubbing

Cause Remedy1) Too Low Voltage

2) Too High Inductance

1) Increase Voltage

2) Reduce Inductance



2) Too High Inductance

3) Excess Slope4) Too Long Stick Out

2) Reduce Inductance

3) Adjust Slope4) Reduce Stick Out

Important Terminology used inCritical Welding

• Preheating• Post Heating or Dehydrogenation

I t di t St l i



• Intermediate Stress leaving

• Inter pass Temperature

• Post Weld Heat Treatment

What Is Preheating?• Heating the base metal along the weld joint to a

predetermined minimum temperature immediately

before starting the weld.• Heating by Oxy fuel flame or electric resistant

coil



coil

• Heating from opposite side of welding wherever possible

• Temperature to be verified by thermo chalks priorto starting the weld

Why Preheating?• Preheating eliminates possible cracking of weld and HAZ

• Applicable to

Hardenable low alloy steels of all thickness

Carbon steels of thickness above 25 mm.



Restrained welds of all thickness

• Preheating temperature vary from 75°C to 200°C

depending on hardenability of material, thickness & joint

restrain

How does Preheating Eliminate Crack?

• Preheating promotes slow cooling of weld and

HAZ• Slow cooling softens or prevents hardening of

eld and HAZ



weld and HAZ

• Soft material not prone to crack even inrestrained condition

What Is Post Heating?• Raising the pre heating temperature of the weld joint to a

predetermined temperature range (250° C to 350° C) for

a minimum period of time (3 Hrs) before the weld coolsdown to room temperature.

• Post heating performed when welding is completed ori d i i b



terminated any time in between.

• Heating by Oxy fuel flame or electric resistant coil• Heating from opposite side of welding wherever possible

• Temperature verified by thermo chalks during the period

Why Post Heating?• Post heating eliminates possible delayed cracking

of weld and HAZ

• Applicable to

Thicker hardenable low alloy steels



y

Restrained hardenable welds of all thickness• Post heating temperature and duration depends on

hardenability of material, thickness & joint

restrain

How does Post Heating Eliminate

Crack?

• SMAW introduces hydrogen in weld metal

• Entrapped hydrogen in weld metal inducesdelayed cracks unless removed before cooling toroom temperature



p

• Retaining the weld at a higher temperature for alonger duration allows the hydrogen to come outof weld

What Is Intermediate Stress Relieving?• Heat treating a subassembly in a furnace to a

predetermined cycle immediately on completion of

critical restrained weld joint / joints withoutallowing the welds to go down the pre heat

temperature. Rate of heating, Soaking temperature,



temperature. Rate of heating, Soaking temperature,

Soaking time and rate of cooling depends onmaterial quality and thickness

• Applicable to

Highly restrained air hardenable material

Why Intermediate Stress Relieving?

• Restrained welds in air hardenable steel highly

prone to crack on cooling to room temperature.



• Cracks due to entrapped hydrogen and built in stress

• Intermediate stress relieving relieves built in stresses

and entrapped hydrogen making the joint free from

crack prone

What Is Inter- Pass Temperature?• The temperature of a previously layed weld bead

immediately before depositing the next bead over

it

• Temperature to be verified by thermo chalk prior



to starting next bead

• Applicable to

Stainless Steel

Carbon Steel & LAS with minimum impact

Why Inter Pass Temperature?• Control on inter pass temperature avoids over

heating, there by

Refines the weld metal with fine grains

Improves the notch toughness properties



p g p p

Minimize the loss of alloying elements inwelds

Reduces the distortion

What Is Post Weld Heat Treatment?• Heat treating an assembly on completion of all

applicable welding, in an enclosed furnace with

controlled heating/cooling rate and soaking at a

specific temperature for a specific time.



• Rate of heating, Soaking temperature, Soaking time

and rate of cooling depends on material quality andthickness

• Applicable to

All type of CS & LAS

Why Post Weld Heat Treatment?

• Welded joints retain internal stresses within the

structure

• HAZ of welds remains invariably hardened



• Post Weld Heat Treatment relieves internal stresses

and softens HAZ. This reduces the crackingtendency of the equipment in service

Weldability

• The weldability of a material refers to its

ability to be welded. Many metals andthermoplastics can be welded, but someare easier to weld than others. It greatly






are easier to weld than others. It greatly

influences weld quality and is an importantfactor in choosing which welding processto use.

• Steels

• The weldability of steels is inverselyproportional to a property known as thehardenability of the steel, which measures theease of forming martensite during heat

treatment. The hardenability of steel depends onits chemical composition, with greaterquantities of carbon and other alloying elementsresulting in a higher hardenability and thus al ld bilit I d t b bl t j d


http://en.wikipedia.org/wiki/Hardenability





http://en.wikipedia.org/wiki/Hardenability





lower weldability. In order to be able to judge

alloys made up of many distinct materials, ameasure known as the equivalent carboncontent is used to compare the relativeweldabilities of different alloys by comparingtheir properties to a plain carbon steel.

• The effect on weldability of elements likechromium and vanadium, while not asgreat as carbon, is more significant thanthat of copper and nickel, for example. Asthe equivalent carbon content rises, the

weldability of the alloy decreases. Thedisadvantage to using plain carbon andlow-alloy steels is their lower strength—th i t d ff b t t i l

http://en.wikipedia.org/wiki/Equivalent_carbon_content







http://en.wikipedia.org/wiki/Chromium

http://en.wikipedia.org/wiki/Vanadium







http://en.wikipedia.org/wiki/Vanadium

http://en.wikipedia.org/wiki/Chromium




there is a trade-off between material

strength and weldability. High strength,low-alloy steels were developed especiallyfor welding applications during the 1970s,and these generally easy to weld materials

have good strength, making them ideal formany welding applications.

• Stainless steels, because of their high chromiumcontent, tend to behave differently with respectto weldability than other steels. Austenitic gradesof stainless steels tend to be the most weldable,but they are especially susceptible to distortion

due to their high coefficient of thermalexpansion. Some alloys of this type are prone tocracking and reduced corrosion resistance aswell. Hot cracking is possible if the amount off it i th ld i t t ll d t ll i t

http://en.wikipedia.org/wiki/HSLA_Steel


http://en.wikipedia.org/wiki/1970s



http://en.wikipedia.org/wiki/1970s






http://en.wikipedia.org/wiki/Ferrite






ferrite in the weld is not controlled—to alleviate

the problem, an electrode is used that deposits aweld metal containing a small amount of ferrite.Other types of stainless steels, such as ferriticand martensitic stainless steels, are not aseasily welded, and must often be preheated and

welded with special electrodes.

• Aluminum

• The weldability of aluminum alloys varies significantly,depending on the chemical composition of the alloy used.

Aluminum alloys are susceptible to hot cracking, and tocombat the problem, welders increase the welding speed tolower the heat input. Preheating reduces the temperature

gradient across the weld zone and thus helps reduce hotcracking, but it can reduce the mechanical properties of thebase material and should not be used when the basematerial is restrained. The design of the joint can bechanged as well and a more compatible filler alloy can be








changed as well, and a more compatible filler alloy can beselected to decrease the likelihood of hot cracking.

Aluminum alloys should also be cleaned prior to welding,with the goal of removing all oxides, oils, and loose particlesfrom the surface to be welded. This is especially importantbecause of an aluminum weld's susceptibility to porosity dueto hydrogen and dross due to oxygen.

• References

• Lincoln Electric (1994). The Procedure Handbookof Arc Welding. Cleveland: Lincoln Electric. ISBN9994925822.

• Residual stresses are stresses that remain afterthe original cause of the stresses has beenremoved. Residual stresses occur for a variety ofreasons, including inelastic deformations and heatt t t H t f ldi l li d

http://en.wikipedia.org/wiki/Oxide

http://en.wikipedia.org/wiki/Oil

http://en.wikipedia.org/wiki/Porosity


http://en.wikipedia.org/wiki/Dross



http://en.wikipedia.org/wiki/Dross


http://en.wikipedia.org/wiki/Porosity

http://en.wikipedia.org/wiki/Oil

http://en.wikipedia.org/wiki/Oxide

http://en.wikipedia.org/wiki/1994

http://en.wikipedia.org/wiki/Cleveland

http://en.wikipedia.org/w/index.php?title=Special:Booksources&isbn=9994925822


http://en.wikipedia.org/wiki/Stress_%28physics%29



http://en.wikipedia.org/wiki/Stress_%28physics%29



http://en.wikipedia.org/wiki/Cleveland

http://en.wikipedia.org/wiki/1994




treatment. Heat from welding may cause localized

expansion, which is taken up during welding byeither the molten metal or the placement of partsbeing welded. When the finished weldment cools,some areas cool and contract more than others,leaving residual stresses. Castings may also havelarge residual stresses due to uneven cooling.

• While un-controlled residual stresses are undesirable,

many designs rely on them. For example, toughenedglass and pre-stressed concrete depend on them toprevent brittle failure. Similarly, a gradient in martensite formation leaves residual stress in some swords withparticularly hard edges (notably the katana), which canprevent the opening of edge cracks. In certain types of

gun barrels made with two tubes forced together, theinner tube is compressed while the outer tube stretches,preventing cracks from opening in the rifling when thegun is fired. Parts are often heated or dunked in liquid

it t id bl



http://en.wikipedia.org/wiki/Glass


http://en.wikipedia.org/wiki/Pre-stressed_concrete

http://en.wikipedia.org/wiki/Brittle


http://en.wikipedia.org/wiki/Hardness

http://en.wikipedia.org/wiki/Katana



http://en.wikipedia.org/wiki/Katana

http://en.wikipedia.org/wiki/Hardness


http://en.wikipedia.org/wiki/Brittle









nitrogen to aid assembly.

• Press fits are the most common intentional use ofresidual stress. Automotive wheel studs, for example arepressed into holes on the wheel hub. The holes aresmaller than the studs, requiring force to drive the studsinto place. The residual stresses fasten the partstogether. Nails are another example.


http://en.wikipedia.org/wiki/Nail

http://en.wikipedia.org/wiki/Nail





Resistance WeldingCommonly used resistance welding processes:

• Resistance Spot Welding (RSW),

• Resistance Seam Welding (RSEW),&

• Resistance Projection Welding (PW) or

(RPW)




( )

• Resistance welding uses the application ofelectric current and mechanical pressure tocreate a weld between two pieces ofmetal. Weld electrodes conduct the electric

current to the two pieces of metal as they areforged together.

• The welding cycle must first develop sufficientheat to raise a small volume of metal to themolten state. This metal then cools while underpressure until it has adequate strength to hold

the parts together. The current density andpressure must be sufficient to produce a weldnugget, but not so high as to expel molten metalf th ld




from the weld zone.

• High Frequency Resistance Welding (HFRW)

Percussion Welding (PEW) and Stud Welding

(SW), too.

WeldNugget

ElectrodeH = I2

R t K

K- energy losses through radiation &conduction

•resistances of the electrodes

•electrode- w/p contact resistance•resistance of the individual parts to

be welded

•w/p-w/p contact resistance




Resistance WeldingBenefits

• High speed welding

• Easily automated

• Suitable for high rateproduction

• Economical

Electrode

HAZ

(maintained high)

• Resistance Welding Limitations

• Initial equipment costs

• Lower tensile and fatigue strengths

• Lap joints add weight and material

Common Resistance Welding Concerns




•Optimize welding process variables.

•Evaluate current welding parameters andtechniques.

• And thus eliminate common welding problems anddiscontinuities - such as

Resistance Welding Problems andDiscontinuities

• Cracks

• Electrode deposit on work

• Porosity or cavities

• Pin holes




Pin holes

• Deep electrode indentation• Improper weld penetration

• Surface appearance

• Weld size

• Irregular shaped welds

RESISTANCE SPOT WELDING



Dr. N. RAMACHANDRAN, NITC 420• AIR OPERATED ROCKER ARM SPOT WELDING MACHINE

RESISTANCE SPOT WELDING




ELECTRODE DESIGNS FOR EASY ACCESS INTO COMPONENTS

RESISTANCE SEAM WELDING




RESISTANCE PROJECTION WELDING




HIGH FREQUENCY BUTT WELDING OF TUBES




FLASH WELDING




FOR SOLID RODS & TUBES DESIGN GUIDELINES

GOODPOOR



RESISTANCE STUD WELDING




http://www.contractconnections.co.nz/images/s4.jpg




UNDERWATER WELDING



DISTORTION• Welding involves highly localized heating of the

metal being joined together .

• The temperature distribution in the weldment isnonuniform.

• Normally, the weld metal and the heat affected zone(HAZ) are at temperatures substantially above that ofthe unaffected base metal.

• Upon cooling, the weld pool solidifies and shrinks,exerting stresses on the surrounding weld metal and




exerting stresses on the surrounding weld metal and

HAZ.• If the stresses produced from thermal expansion and

contraction exceed the yield strength of the parentmetal, localized plastic deformation of the metaloccurs.

• Plastic deformation results in lasting change in thecomponent dimensions and distorts thestructure. This causes distortion of weldments.

Types of distortion

• Longitudinal shrinkage

• Transverse shrinkage• Angular distortion• Bowing• Buckling




• Twisting

Effects of expansion and

contraction




CONTROLLING DISTORTION




HEAT AFFECTED ZONE




Factors affecting distortion

• If a component were uniformly heated and cooleddistortion would be minimized. However, weldinglocally heats a component and the adjacent cold metal

restrains the heated material. This generates stressesgreater than yield stress causing permanent distortionof the component. Some of the factors affecting thedistortion are:




1. Amount of restraint2. Welding procedure

3. Parent metal properties

4. Weld joint design

5. Part fit up

• Restraint - to minimize distortion. Components welded

without any external restraint are free to move or distortin response to stresses from welding. It is not unusualfor many shops to clamp or restrain components to bewelded in some manner to prevent movement anddistortion. This restraint does result in higher residual

stresses in the components.• Welding procedure impacts the amount of distortion

primarily due to the amount of the heat inputproduced. The welder has little control on the heat inputspecified in a welding procedure This does not prevent




specified in a welding procedure. This does not preventthe welder from trying to minimize distortion. While thewelder needs to provide adequate weld metal, thewelder should not needlessly increase the total weldmetal volume added to a weldment.

• Parent metal properties, which have an effect ondistortion, are coefficient of thermal expansion andspecific heat of the material. The coefficient of thermalexpansion of the metal affects the degree of thermalexpansion and contraction and the associated stressesthat result from the welding process. This in turndetermines the amount of distortion in a component.

• Weld joint design will effect the amount of distortion in aweldment. Both butt and fillet joints mayexperience distortion. However, distortion is easier to




p ,

minimize in butt joints.• Part fit up should be consistent to fabricate foreseeable

and uniform shrinkage. Weld joints should beadequately and consistently tacked to minimizemovement between the parts being joined by welding.

Welding Discontinuities

Some examples of welding discontinuities areshown below.Evaluation of the discontinuity will determine if the

discontinuity is a defect or an acceptable condition




Incomplete Fusion - A weld discontinuity inwhich fusion did not occur between weld metaland fusion faces or adjoining weld beads.




Undercut - A groove melted into the base metal adjacent to the weld toe orweld root and left unfilled by weld metal.

Overlap - The protrusion of weld metal beyond the weld toe or weld root.

Underfill - A condition in which the weld face or root surface extends below theadjacent surface of the base metal.

Incomplete Joint Penetration - A joint root condition in a groove weld in which




p j g

weld metal does not extend through the joint thickness

•Partial joint penetration groove welds are commonly specified in lowly loadedstructures. However, incomplete joint penetration when a full penetration joint isrequired, as depicted above, would be cause for rejection. A fix for anincomplete penetration joint would be to back gouge and weld from the other

side. Another acceptable partial penetration joint is shown below.

Partial penetration joint on the left without discontinuities is anacceptable condition.




Appropriate engineering decisions need to be applied todetermine what type of joint should be specified for a givenapplication.




Several different representations of weld Cracking




Representation of a convex fillet weld without discontinuities




WELD BEND TEST

Nick break test




SOLID STATE PROCESSES

• Joining without fusion of work pieces

• No liquid (molten ) phase present in joint• Principle: If two clean surfaces are brought into

atomic contact with each other - made with

sufficient pressure -(in the absence of oxide film




sufficient pressure (in the absence of oxide film

and other contaminents) they form bonds and

produce strong joint

• To improve strength, heat and some movement of

mating surfaces by plastic deformation employed.Eg: USW, Friction Welding (FRW)

FORGE WELDING (FOW)

• Both elevated temperature and pressure applied

to form strong bond between members

• Components heated and pressed/ hammered

with tools, dies or rollers




• Local plastic deformation at interface breaks upthe oxide films – improves bond strength.

• Not for high load bearing applications.

COLD WELDING (CW)

• Pressure applied to work pieces either through dies

or rolls• One (or both) of the mating parts must be ductile

• Interface cleaned prior to welding- brushing etc.




Roll

Rolling metal

Bare metal

Explosive welding• Solid state bonding process

• Joining by the cohesive force between atoms of twointimate contact surfaces

High pressure waves- thousands of MPa created-

• To weld dissimilar metals, thick to thin, high differencein Melting Point metals.

• Not a costly process

• Extremely large surfaces can be joined (2m X 10 m)




Extremely large surfaces can be joined (2m X 10 m)

• Welding of heat treated metals without affecting theprocess

• No HAZ

• Incompatible metals joined(thin foils to heavy plates)

severe deformation needed for joining.

• Principle:

Explosive Impulse used to produceextremely high normal pressure and a slightshear or sliding pressure ( uses a detonator forthis)

Two properly laid metal surfaces brought together with highrelative velocity at high pressure and with properorientation




Large amount of plastic interaction between surfaces

results. TWO WAYS

(1)Contact technique(2) Impact technique

• (1). Plastic interaction by positioning

explosive charge to deliver shock waves atan oblique angle to parts to be welded- Less

frequently used.




• (2). Two pieces explosively projectedtowards each other.

• Impact with high velocity (200 – 400 m/s)

•Plastic interaction by positioning explosive charge to deliver shock

waves at an oblique angle to parts to be welded- Less frequently

used.

(1)Contact technique




(2) Impact technique

Two pieces explosively projected towards each other.Impact with high velocity (200 – 400 m/s)




• Detonation velocity approx. 7000 m/s in thedetonation front.

• Produces pressure at interface 7000 to 70,000atms. Parts driven at an angle Velocity of impactand angle of collapse selected. Joining as s resultof intense plastic flow at the surface called“surface jetting”

• For good joint, surface to be free fromcontaminants




contaminants

• Pressure sufficient to bring surfaces withininteratomic distances of each other [ In a range ofspeed and angle of impact, a high velocity metal

jet forms. Removes surface contamination. Speed,angle(10 to 100) of detonation important]

• Bond as strong as the weaker of the twoobtained. 100 % efficient joint, (eg. In sheetforming in aerospace industries)

• At the interface, microhardness slightlyincreased. (because of plastic deformation




and strain hardening- a very thin hardnesszone)

• Titanium cladding common• Others- Ni, SS(50 mm), tantalum, carbon steels,

for heat exchangers, tubes, pressure vessels, etc.

• No change in chemical and physical properties

of parent metal• But, not for brittle alloys. Metal must possess

some ductility.

• [Quantity of charge, detonation velocity, and




deformation characteristics of flyer plate decidethe weld]

• Also spot welding by small charge. Handyexplosive spot welding sets available (for 10mm

to 12 mm spots)

• Minus points: Severe deformation needed

for joining (minimum 40 to 60%), as

welding is by pressure.




THERMIT WELDING• THERMITE- based on Therm, meaning heat

• Involves exothermic reactions between metal oxides and metallic reducingagents

• Heat of reaction used for welding.

•

• Fine particles of iron oxide, aluminium oxide, iron & aluminium




• Reactions are: (3/4) Fe3 O4 + 2 Al --- (9/4) Fe + Al2O3 + Heat

3 FeO + 2 Al --- 3 Fe + Al2O3 + Heat

Fe2O3 + 2Al --- 2Fe + Al2O3+ Heat

THERMIT WELDING



Thermit Welding



• Mixture is non explosive. Produces temperature of32000 C within a minute

• Practically about 22000- 24000 C. Other materials toimpart special properties added. Applying a Mg fuse of

special compounds of peroxides, chlorates/ chromates.




• Welding copper, brasses, bronzes and copper alloys to

steel using oxides of copper, nickel, aluminium,

manganese – temperatures of 50000 C obtained




THERMIT WELDING OF RAILS



PLASMA

WELDING

• Plasma is commonly known as fourth state of matter after solid, liquid and gas.This is an extremely hot substance which consists of free electrons, positiveions, atoms and molecules. It conducts electricity.How it works:By positioning the electrode within the body of the torch, the plasma arc can beseparated from the shielding gas envelope. Plasma is then forced through afine-bore copper nozzle which constricts the arc. There are three operatingmodes which can be produced by varying bore diameter and plasma gas flowrate:•Microplasma: 0.1 to 15A.

•Medium current: 15 to 200A. •Keyhole plasma: over 100A. The plasma arc is usually operated with a DC, drooping characteristic powersource. Because its unique operating features are results of the special torcharrangement and separate plasma and shielding gas flows, a plasma controlconsole can be added on to a normal TIG power source. Full plasma systemsare also available. The plasma arc is not stabilised with sine wave AC. Arc




reignition is difficult when there is a long electrode to workpiece distance and theplasma is constricted, extreme heating of the electrode during the positive half-cycle causes balling of the tip which can disturb arc stability. Special-purposeswitched DC power sources are available. By misbalancing the waveform toreduce the duration of electrode positive polarity, the electrode is kept passablycool to maintain a pointed tip and achieve arc stability.




• Electrode The electrode used for the plasma process is tungsten-2%thoria and the plasma nozzle is copper. The electrodetip diameter is not as critical as for TIG and should bemaintained at around 30-60 degrees. The plasma nozzlebore diameter is critical and too small a bore diameter forthe current level and plasma gas flow rate will lead to

excessive nozzle erosion or even melting. Large borediameter should be carefully used for the operating currentlevel.Because too large a bore diameter, may give problemswith arc stability and maintaining a keyhole.Plasma and shielding gases




g gThe normal combination of gases is argon for the plasmagas, with argon plus 2 to 5% hydrogen for the shieldinggas. Helium can be used for plasma gas but because it ishotter this reduces the current rating of the nozzle.Helium's lower mass can also make the keyhole mode

more difficult.

http://www.airproducts.com/tmm/tellmemore.asp

http://www.airproducts.com/search/search.asp

http://www.airproducts.com/sitemap.htm




• Applications:

Microplasma welding:Microplasma was traditionally used for welding thin sheets(down to 0.1 mm thickness), and wire and mesh sections.The needle-like stiff arc minimises arc wander anddistortion. Although the alike TIG arc is widely used, thenewer transistorised (TIG) power sources can produce a

very stable arc at low current levels.Medium current welding:When used in the melt mode this is a substitute to normalTIG.The advantages are:




1-Deeper penetration (from higher plasma gas flow).2-Greater tolerance to surface contamination includingcoatings (the electrode is within the body of the torch).The major disadvantage lies in the bulkiness of the torch,making manual welding more difficult. In mechanisedwelding, greater attention must be paid to maintenance of

the torch to ensure consistent performance.

• Keyhole welding: This has several advantages which can beexploited: deep penetration and high weldingspeeds. Compared with the TIG arc, it canpenetrate plate thicknesses up to l0mm, but whenwelding using a single pass technique, it is more

usual to limit the thickness to 6mm. The normalmethods is to use the keyhole mode with filler toensure smooth weld bead profile (with noundercut). For thicknesses up to 15mm, a vee jointpreparation is used with a 6mm root face. A two-




pass technique is employed and here, the firstpass is autogenous with the second pass beingmade in melt mode with filler wire addition.

• As the welding parameters, plasma gas flow

rate and filler wire addition (into the keyhole)must be carefully balanced to maintain thekeyhole and weld pool stability, thistechnique is only suitable for mechanised

welding. Although it can be used forpositional welding, usually with currentpulsing, it is normally applied in high speed




welding of thicker sheet material (over 3 mm)in the flat position. When pipe welding, theslope-out of current and plasma gas flowmust be carefully controlled to close the

keyhole without leaving a hole.

Gas

MIG/TIG

Weldi

ng

Plasma Arc

Weldi

ng

Laser

Weldi

ng

Laser

Cuttin

g

Plasma

Cuttin

g

Oxy-Fuel

Cuttin

g Thermal

Spraying

Acetylene X X

Air X X X

Alumaxx Plus X

Argon X X X X X X

Argon/hydrogen TIG X X

Carbon dioxide MAG X X Cooling

Carbon monoxide X

Ferromaxx Plus MAG

Ferromax 15 MAG

Ferromaxx 7 MAG

Helium TIG X X X

Hydrogen X




y g

Inomaxx Plus MAG

Inomaxx 2 MAG

Inomaxx TIG TIG X

Nitrogen X X X

Nitrogen/hydrogenmixes

X

Oxygen X X X

Propane X X

Propylene X X

The process is simple to operate- Can be used manually or in an automated manner.

Arc Spraying Arc spraying is the highest

productivity thermal sprayingprocess. A DC electric arc is struck betweentwo continuous consumable wireelectrodes which form the spraymaterial.

Compressed gas (usually air)atomises the molten spray materialinto fine droplets and propels themtowards the substrate




Possible to spray a wide range of metals, alloys and metal matrix composites(MMCs) in wire form. A limited range of cermet coatings (with tungsten carbide) can also be sprayed incored wire form, where the hard ceramic phase is packed into a metal sheath as afine powder.The combination of high arc temperature (6000 K) and particle velocities in excess of

100 m.sec-1 gives arc sprayed coatings superior bond strengths and lower porositylevels when compared with flame sprayed coatings.However, the use of compressed air for droplet atomization and propulsion

gives rise to high coating oxide content.

• Because of the high temperature andhigh thermal energy of the plasma jet,materials with high melting pointscan be sprayed.

• Plasma spraying produces a highquality coating by a combination of a

•Uses a DC electric arc to generate astream of high temperature ionised

plasma gas, which acts as the

spraying heat source. •The arc is struck between two non-

consumable electrodes, a tungsten

cathode and a copper anode within the

torch. •The torch is fed with a continuous

flow of inert gas, which is ionised by

the DC arc, and is compressed and

accelerated by the torch nozzle so that

PLASMA SPRAYING PROCESS




high temperature, high energy heatsource, a relatively inert sprayingmedium and high particle velocities,

typically 200 –300 m.sec-1. • However, inevitably some air

becomes entrained in the spraystream and some oxidation of the

spray material may occur. Thesurrounding atmosphere also coolsand slows the spray stream.

it issues from the torch as a high

velocity (in excess of 2000 m/sec),

high temperature (12000 –16000 K)

plasma jet.

•The coating material, in powder form,

is carried in an inert gas stream intothe plasma jet where it is heated and

propelled towards the substrate.

Applications• Plasma spraying is widely applied in the production of high

quality sprayed coatings.

• Spraying of seal ring grooves in the compressor area ofaeroengine turbines with tungsten carbide/cobalt to resistfretting wear.

• Spraying of zirconia-based thermal barrier coatings (TBCs) onto

bi b i h b




turbine combustion chambers.

• Spraying of wear resistant alumina and chromium oxide ceramiconto printing rolls for subsequent laser and diamondengraving/etching.

• Spraying of molybdenum alloys onto diesel engine piston rings.

HIGH VELOCITY OXYFUEL SPRAYING

This differs from conventional flame spraying in that the combustion process is

i l d h fl f d d li h hi h h

The most recent addition to the thermalspraying family, high velocity oxyfuel

spraying (HVOF SPRAYING) has

become established as an alternative to

the proprietary, detonation (D-GUN)

flame spraying and the lower velocity,air plasma spraying processes for

depositing wear resistant tungsten

carbide-cobalt coatings.




internal, and the gas flow fates and delivery pressures are much higher thanthose in the atmospheric burning flame spraying processes.

The combination of high fuel gas and oxygen flow rates and high pressure in the

combustion chamber leads to the generation of a supersonic flame with

characteristic shock diamonds.

Flame speeds of 2000ms-1 and particle velocities of 600 – 800ms-1 are claimed byHVOF equipment suppliers.

A range of gaseous fuels is currently used, including propylene, propane,

hydrogen and acetylene.

• Although similar in principle, potentially

significant details, such as powder feedposition, gas flow rates and oxygen to fuelratio, are apparent between each system.

• The HVOF process produces exceptionallyhigh quality cermet coatings (e.g., WC-Co), but

it is now also used to produce coatings ofmetals, alloys and ceramics. Not all HVOFsystems are capable of producing coatingsfrom higher melting point materials, e.g.,refractory metals and ceramics. The capability

f th i d d t th f f l




of the gun is dependent upon the range of fuelgases used and the combustion chamberdesign.

• A liquid fuel (kerosene) HVOF system, has just

been launched, which is capable of muchhigher deposition rates than the conventionalgas-fuelled units.

HVOF spraying is a very recent process development, yet the high

quality of the coatings produced at competitive cost has already seen its

introduction in a number of very significant industries. Potential

applications overlap with plasma and D-gun spraying, particularly for

WC-Co coatings.

Tungsten carbide-cobalt coatings for fretting wear resistance on

aeroengine turbine components.

Wear resistant cobalt alloys onto fluid control valve seating areas.

T t bid b lt ti t l

Applications




Tungsten carbide-cobalt coatings on gate valves.

Various coatings for printing rolls, including copper, alumina, chromia.

NiCrBSi coatings (unfused) for glass plungers.

NiCr coatings for high temperature oxidation/corrosion resistance.

Alumina and alumina-titania dielectric coatings.

Biocompatible hydroxylapatite coatings for prostheses.

Schematic of High Velocity Oxyfuel (HVOF) Spraying System

Process

Particle

Velocity

(m/s) Adhesion (MPa) Oxide Content

(%) Porosity (%) Deposition Rate

(kg/hr)

Typical Deposit

Thicknes

s (mm)




Flame 40 <8 10 –15 10 –15 1 –10 0.2 –10

Arc 100 10 –30 10 –20 5 –10 6 –60 0.2 –10

Plasma 200 –300 20 –70 1 –3 1 –8 1 –5 0.2 –2

HVOF 600 –800 >70 1 –2 1 –2 1 –5

Comparison of Thermal Spraying Processes and Coating

Characteristics

Process Particle Velocity (m/s) Adhesion (MPa) Oxide Content (%) Porosity (%)

Deposition Rate

(kg/hr)

Typical Deposit

Thickness

(mm)

Flame 40 <8 10 –15 10 –15 1 –10 0.2 –10

Arc 100 10 –30 10 –20 5 –10 6 –60 0.2 –10




Plasma 200 –300 20 –70 1 –3 1 –8 1 –5 0.2 –2

HVOF 600 –800 >70 1 –2 1 –2 1 –5

Thermal Spraying Gases

Process Fuels that can be used Other gases

HVOF Acetylene, hydrogen, propylene, propane, or liquidkerosene depending on material type

Oxygen and argon

Arc spraying Normally compressed air but can use nitrogen or argon




Flame spraying Mainly acetylene, but sometimes propane depending onmaterial

Oxygen

Plasma spraying Argon and hydrogen

Electro slag weldingSome references site Robert Hopkins forhaving invented the Electroslag weldingprocess in the 1930's. Most of his patentsrelate to Electroslag melting for ingot

manufacture, not welding. However oneUS patent, number 2,191481 filed in June,1939 does describe the surfacing of onematerial on another. The illustration,however looks more like a melting furnacethan welding. In fact the fellow who

i t d S b d A W ldi H






invented Submerged Arc Welding, HarryKennedy, was granted a US patent inOctober of 1950, number 2,631,344,assigned to Union Carbide that moreclosely related to Electroslagwelding. However it too falls short of

defining what we know today as thissimple welding process.








Electro Slag Welding




ELECTROGAS WELDING


















Slide 14 of 18

ELECTRON BEAM WELDING•The electron beam gun has a

tungsten filament which is heated,freeing electrons.

•The electrons are accelerated fromthe source with high voltagepotential between a cathode and

anode.

•The stream of electrons then passthrough a hole in the anode. Thebeam is directed by magneticforces of focusing and deflecting

coils This beam is directed out of



coils. This beam is directed out ofthe gun column and strikes theworkpiece.

•The potential energy of theelectrons is transferred to heat

upon impact of the workpiece andcuts a perfect hole at the weld joint.Molten metal fills in behind thebeam, creating a deep finishedweld.

• The electron beam stream and

workpiece are manipulated bymeans of precise, computerdriven controls, within a vacuum

ldi h b th f




welding chamber, thereforeeliminating oxidation,

contamination.

How an Electron Beam Machine Works

• The EB system is composed of anelectron beam gun, a power supply,

control system, motion equipment andvacuum welding chamber. Fusion of basemetals eliminates the need for filler metals.

Th i t f ti f




The vacuum requirement for operation ofthe electron beam equipment eliminatesthe need for shielding gases and fluxes.

• Electron Beam Welding (EBW) is a unique way of delivering large amounts of concentrated thermalenergy to materials being welded. It became viable,as a production process, in the late 1950's. At thattime, it was used mainly in the aerospace andnuclear industries. Since then, it has become the

welding technique with the widest range ofapplications. This has resulted from the ability to usethe very high energy density of the beam to weldparts ranging in sizes from very delicate smallcomponents using just a few watts of power, to

welding steel at a thickness of 10 to 12 inches with




welding steel at a thickness of 10 to 12 inches with100 Kilowatts or more. However, even today most ofthe applications are less than 1/2" in thickness, andcover a wide variety of metals and even dissimilarmetal joints

ELECTRON BEAM WELDING


















Slide 16 of 18

ELECTRON BEAM WELDING


















Slide 15 of 18




• Two welding modes are used in the (EBW):1-Conductance mode:Mainly applicable to thin materials, heating of the weld joint to meltingtemperature is quickly generated at or below the materials surface followed bythermal conductance throughout the joint for complete or partial penetration.The resulting weld is very narrow for two reasons:a- It is produced by a focused beam spot with energy densities concentratedinto a .010 to.030 area.b- The high energy density allows for quick travel speeds allowing the weld tooccur so fast that the adjacent base metal does not absorb the excess heat

therefore giving the E.B. process it's distinct minimal heat affected zone.2-Keyhole mode:It is employed when deep penetration is a requirement. This is possible sincethe concentrated energy and velocity of the electrons of the focused beam arecapable of subsurface penetration. The subsurface penetration causes therapid vaporization of the material thus causing a hole to be drilled through thematerial. In the hole cavity the rapid vaporization and sputtering causes a

pressure to develop thereby suspending the liquidus material against thecavity walls As the hole is advanced along the weld joint by motion of the




pressure to develop thereby suspending the liquidus material against thecavity walls. As the hole is advanced along the weld joint by motion of theworkpiece the molten layer flows around the beam energy to fill the hole andcoalesce to produce a fusion weld. The hole and trailing solidifying metalresemble the shape of an old fashion keyhole.Both the conductance and keyhole welding modes share physical featuressuch as narrow welds and minimal heat affected zone .The basic difference isthat a keyhole weld is a full penetration weld and a conductance weld usuallycarries a molten puddle and penetrates by virtue of conduction of thermalenergy.

Electron Beam Welding• Electron Beam Welding joins ferrous metals, light

metals, precious metals, and alloys, to themselves or

each other.• Multi-axis EB control• High ratio of depth-to-width• Maximum penetration with minimal distortion • Exceptional weld strength

• Ability to weld components up to 10 feet in diameterHi h i i d t bilit ith i t ll 0%




• Ability to weld components up to 10 feet in diameter • High precision and repeatability with virtually 0% scrap • Versatility from .002" depth to 3.00" depth ofpenetration

Electron Beam Welding Facts

• Electron Beam Welding Advantages • Maximum amount of weld penetration with the least amount of heatinput reduces distortion• Electron beam welding often reduces the need for secondaryoperations• Repeatability is achieved through electrical control systems • A cleaner, stronger and homogeneous weld is produced in avacuum• The electron beam machine's vacuum environment eliminatesatmospheric contaminates in the weld

• Exotic alloys and dissimilar materials can be weldedE t i i d t CNC i d ifi ti f




Exotic alloys and dissimilar materials can be welded • Extreme precision due to CNC programming and magnification ofoperator viewing• Electron beam welding frequently yields a 0% scrap rate • The electron beam process can be used for salvage and repair ofnew and used components




Electron Beam Welding Speeds/Depth of Penetration

• Electron BeamWeldingLimitations • The necessity of an

electron beamwelding vacuumchamber limits thesize of the workpiece

EBTEC's




— EBTEC smaximum chambersize is 11' 4" wide x9' 2" high x 12' deep

Electron Beam Welding Speeds/Depth of Penetration

LASER BEAM WELDING(LBW)• LASER - Light Amplification by Stimulated

Emission of R adiation

• Focusing of narrow monochromatic light intoextremely concentrated beams (0.001 mm even)

• Used to weld difficult to weld materials, hard to

access areas extremely small components In




access areas, extremely small components, Inmedical field to weld detached retinas back intoplace

• Laser Beam- coherent

Laser production- complex process.

The LASER, an

acronym for "Light

Amplification by

Stimulated Emission

of Radiation," is a

device that producesa concentrated,

coherent beam of

light by stimulating

molecular orl t i t iti




molecular orelectronic transitions

to lower energy

levels, causing the

emission of photons.

Al2O3 + 0.05% Chromium

• solid state RubyLaser- Neon flash tube emits lightinto specially cut ruby crystals- absorbs light -electrons of chromium atoms get stimulated-

• Increase in stimulation ---- electrons increase from

normal(ground) orbit to an exited orbit. Moreenergy input- energy absorbed exceeds thermalenergy- no longer to heat energy.

• Electrons drop back to intermediate orbit- emits

PHOTONS (light) called spontaneous emission




PHOTONS (light) called spontaneous emission• With continued emission, released photons

stimulate other exited electrons to release photons-called stimulated emission

• Causes exited electrons to emit photons of samewave length.

• Power intensities > 10 kw/cm2

• No physical contact between work and weldingequipment

• 2 mirrors- coherent light reflected back and forth, becomes dense, penetrates partially reflective mirror,

focused to the exact point• Very little loss of beam energy

• Solid state, liquid, semiconductor and gas lasers used.

• Solid state uses light energy to stimulate electronsR b N d i YAG




Solid state uses light energy to stimulate electronsRuby, Neodymium, YAG

• Gas lasers use electrical charge to stimulate electronsGas lasers- higher wattage outputs. Used for thicker

sections - CO2, N2, He• Liquid- nitrobenzene; Gas- based on gallium arsenide

Laser Welding Facts

• Laser Welding Advantages • Processes high alloy metals without difficulty • Can be used in open air • Can be transmitted over long distances with a

minimal loss of power• Narrow heat affected zone • Low total thermal input • Welds dissimilar metals • No filler metals necessary • No secondary finishing necessary




No secondary finishing necessary • Extremely accurate • Welds high alloy metals without difficulty

• CO2 Laser Welding Speeds

• The solid-state laser utilizes a single

crystal rod with parallel, flat ends. Bothends have reflective surfaces. A high-intensity light source, or flash tube

surrounds the crystal. When power issupplied by the PFN (pulse-formingnetwork), an intense pulse of light

(photons) will be released through one endf th t l d Th li ht b i l d




(photons) will be released through one endof the crystal rod. The light being releasedis of single wavelength, thus allowing forminimum divergence

• One hundred percent of the laser light will bereflected off the rear mirror and thirty to fiftypercent will pass through the front mirror,continuing on through the shutter assembly tothe angled mirror and down through the focusinglens to the workpiece.

• The laser light beam is coherent and has a highenergy content. When focused on a surface,laser light creates the heat used for welding,cutting and drilling.

• The workpiece and the laser beam aremanipulated by means of robotics The laser




The workpiece and the laser beam aremanipulated by means of robotics. The laserbeam can be adjusted to varying sizes and heatintensity from .004 to .040 inches. The smallersize is used for cutting, drilling and welding and

the larger, for heat treating

Laser Welding Limitations

• Rapid cooling rate may cause

cracking in certain metals

• High capital cost

• Optical surfaces easily damaged

• High maintenance cost




LASER WELDING


















Slide 17 of 18

LASER WELDING














Slide 18 of 18

Laser beam cutting• Along with beam, oxygen used to help

cutting. Ar, He, N, CO2 also for steel, alloysetc.

Two ways to weld

1. Work piece rotated or moved past beam

2. Many pulses of laser (10 times/sec)used.




Narrow HAZ., speeds of 40 mm/sec to 1.5 m/sec

Cooling system to remove the heat-

gas and liquid cooling used

• Klyston tubes (glass to metal sealing),capacitor bank, tr igger ing device, flash

tube, focusing lens, etc. in the setup.

• Cathode of molybdenum, tantalum orti tanium used.




1987

Laser research begins a unique method for depositing complex

metal alloys (Laser Powder Fusion).

2002

From Linde Gas in Germany, a Diode laser using process gases

and "active-gas components" is investigated to enhance the "key-

holing" effects for laser welding. The process gas, Argon-CO2,increases the welding speed and in the case of a diode laser, will

support the transition of heat conductivity welding to a deep

welding, i.e., 'key-holing'. Adding active gas changes the direction

of the metal flow within a weld pool and produces narrower, high-

quality weld.




quality weld.

CO2 Lasers are used to weld polymers. The Edison Welding

Institute is using through-transmission lasers in the 230-980 nm

range to readily form welded joints. Using silicon carbides

embedded in the surfaces of the polymer, the laser is capable ofmelting the material leaving a near invisible joint line.




Friction stir welding

• The advantage of this solid-state process is that it’s producing welds between extruded aluminium profiles through friction heating without theneed for either shielding gas or filler metal.

• The maximum length of welding is 16m, and by welding many profilestogether, one can produce panels up to 20 metres in width. Onlyaluminium alloys in the 6xxx-series are certified for production. The profilethickness varies from 2mm to 12mm, at certified welding speeds up to3.6m/min.

• The surface of the resulting panels is smooth, and requires no further

grinding or brushing to improve the finish.• The lower heat required for welding the profiles means that there is less




• The lower heat required for welding the profiles means that there is lessdistortion, and the technology produces panels with better mechanical

properties than fusion welded.

• At time of acquisition, this was the first production machine of its kind inthe world. From 01/97-09/04 app. 465.000m of FSW welding have been

produced.



Dr. N. RAMACHANDRAN, NITC 532Rotary Friction Stir Welding Twin Stir Variants



Dr. N. RAMACHANDRAN, NITC 533Reversal Stir Technique

Soldering and Brazing•Soldering and Brazing are joining

processes where parts are joined without melting the base

metals.

•Soldering filler metals meltbelow 450 °C.

•Brazing filler metals meltabove 450 °C.

(De)soldering a contact from a wire



(De)soldering a contact from a wire

•Soldering is commonly used for electrical connection ormechanical joints, but brazing is only used for mechanical

joints due to the high temperatures involved

Soldering

• A method of joining metal parts using an alloy oflow melting point (solder ) below 450 °C (800 °F).

• Heat is applied to the metal parts, and the alloymetal is pressed against the joint, melts, and isdrawn into the joint by capillary action andaround the materials to be joined by 'wetting

action'.


http://en.wikipedia.org/wiki/Melting_point

http://en.wikipedia.org/wiki/Solder

http://en.wikipedia.org/wiki/Capillary_action

http://en.wikipedia.org/wiki/Wetting





http://en.wikipedia.org/wiki/Solder

http://en.wikipedia.org/wiki/Melting_point





• After the metal cools, the resulting joints are

not as strong as the base metal, but haveadequate strength, electrical conductivity, andwater-tightness for many uses.

Soldering and Brazing Benefits

• Economical for complex assemblies

• Joints require little or no finishing

• Excellent for joining dissimilar metals

• Little distortion, low residual stresses

• Metallurgical bond is formedSound electrical component connections





g• Sound electrical component connections

Soldering can be done in a number of

waysIncluding passing parts over a bulk container of meltedsolder, using an infrared lamp, or by using a pointsource such as an electric soldering iron, a brazing torch, or a hot-air soldering tool.

A flux is usually used to assist in the joining process.

Flux can be manufactured as part of the solder in singleor multi-core solder, in which case it is containedinside a hollow tube or multiple tubes that arecontained inside the strand of solder.

Flux can also be applied separately from the solder,often in the form of a paste.

I fl l ld i f i th t i

http://en.wikipedia.org/wiki/Infrared

http://en.wikipedia.org/wiki/Electric

http://en.wikipedia.org/wiki/Soldering_iron

http://en.wikipedia.org/wiki/Brazing




http://en.wikipedia.org/wiki/Soldering_iron

http://en.wikipedia.org/wiki/Electric

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In some fluxless soldering, a forming gas that is areducing atmosphere rich in hydrogen can also servemuch the same purpose as traditional flux, andprovide the benefits of traditional flux in re-flow ovens

through which electronic parts placed on a circuitcard are transported for a carefully timed period oftime.

• One application ofsoldering is making

connections betweenelectronic parts andprinted circuit boards.

• Another is in plumbing.

Joints in sheet-metalobjects such as cansfor food, roof flashing,and drain gutters werealso traditionallysoldered.

Soldering canalso be used as arepair technique

http://en.wikipedia.org/wiki/Printed_circuit_board

http://en.wikipedia.org/wiki/Plumbing

http://en.wikipedia.org/wiki/Jewelry

http://en.wikipedia.org/wiki/Plumbing

http://en.wikipedia.org/wiki/Printed_circuit_board




• Jewelry and smallmechanical parts areoften assembled bysoldering.

to patch a leak ina container orcooking vessel.

• Soldering is distinct from welding in that

the base materials to be joined are notmelted, though the base metal is dissolvedsomewhat into the liquid solder much as a

sugar cube into cof fee - this dissolutionprocess results in the soldered joint'smechanical and electrical strengths.

• A "cold solder joint" with poor propertieswill result if the base metal is not warm








j p p pwill result if the base metal is not warmenough to melt the solder and cause thisdissolution process to occur.

• Due to the dissolution of the base metals into the

solder, solder should never be reused• Once the solder's capacity to dissolve base

metal has been achieved, the solder will notproperly bond with the base metal and a cold

solder joint with a hard and brittle crystallineappearance will usually be the result.

• It is good practice to remove solder from a jointprior to resoldering - desoldering wicks orvacuum desoldering equipment can be used.




g q p

• Desoldering wicks contain plenty of flux that willlift the contamination from the copper trace and

any device leads that are present. This will leavea bright, shiny, clean junction to be resoldered.

• The lower melting point of solder

means it can be melted away from thebase metal, leaving it mostly intact

through the outer layer.

• It will be "tinned" with solder.• Flux will remain which can easily be

removed by abrasive or chemical

processes.




p• This tinned layer will allow solder to

flow into a new joint, resulting in a new

joint, as well as making the new solderflow very quickly and easily.



• Basic electronic soldering techniques

All solder pads and device terminals must be clean forgood wetting and heat transfer.

The soldering iron or gun must be clean, otherwisecomponents may heat up excessively due to poor heat

transfer.The devices must then be mounted on the circuit board

properly.

One technique is to elevate the components from the board

surface (a few millimeters) to prevent heating of thecircuit board during circuit operation.


http://en.wikipedia.org/wiki/Circuit_board

http://en.wikipedia.org/wiki/Circuit_board





After device insertion, the excess leads can be cut leavingonly a length equal to the radius of the pad.

Plastic mounting clips or holders are used for large devices

to reduce mounting stresses.



• Be sure not to move the joint while it is cooling. Doing sowill result in a fractured joint.

• Do not blow air onto the joint while it is cooling; Instead,let it cool naturally, which will occur fairly rapidly.

• A good solder joint is smooth and shiny. The lead outlineshould be clearly visible. Clean the soldering iron tipbefore you begin on a new joint. It is absolutelyimportant that the iron tip be free of residual flux.

• Excess solder should be removed from the tip. Thissolder on the tip is known as keeping the tip tinned. Itaids in heat transfer to the joint.

• After finishing all of the joints, remove excess fluxresidue from the board using alcohol, acetone, or otherorganic solvents.I di id l j i t b l d h i ll




• Individual joints can be cleaned mechanically.

• The flux film fractures easily with a small pick and can beblown away with canned air.

• In solder formulations with water-soluble fluxes,sometimes pressurized carbon dioxide or distilled waterare used to remove flux.

• Traditional solder for electronic joints is a

60/40 Tin/Lead mixture with a rosin basedflux that requires solvents to clean theboards of flux.

• Environmental legislation in many countries, andthe whole of the European Communi ty area ,have led to a change in formulation.

• Water soluble non-rosin based fluxes have beenincreasingly used since the 1980's so that

http://en.wikipedia.org/wiki/European_Community

http://en.wikipedia.org/wiki/European_Community




increasingly used since the 1980 s so thatsoldered boards can be cleaned with water orwater based cleaners. This eliminates

hazardous solvents from the productionenvironment, and effluent.

Lead-free electronic soldering

• More recently environmental legislation

has specifically targeted the wide use oflead in the electronics industry. Thedirectives in Europe require many newelectronic circuit boards to be lead free by1st July 2006, mostly in the consumer




y , ygoods industry, but in some others as well.

• Many new technical challenges havearisen, with this endeavour.

• For instance, traditional lead free solders have asignificantly higher melting point than lead basedsolders, which renders them unsuitable for use with heatsensitive electronic components and their plasticpackaging. To overcome this problem solder alloys witha high silver content and no lead have been developedwith a melting point slightly lower than traditional solders.

• Not using lead is also extended to components pins andconnectors. Most of those pins were using copperframes, and either lead, tin, gold or other finishes. Tin-finishes is the most popular of lead-free finishes.However, this poses nevertheless the question of tin-

whiskers. Somehow, the current movement brings theelectronic industry backs to the problems solved 40b ddi l d

http://en.wikipedia.org/wiki/Whisker_%28metallurgy%29








years ago by adding lead.• A new classification to help lead-free electronic

manufacturers decide what kind of provisions they wantto take against whiskers, depending upon theirapplication criticity.

Stained glass soldering

• Historically soldering tips were copper, placed inbraziers. One tip was used; when the heat hadtransferred from the tip to the solder (and depleted theheat reserve) it was placed back in the brazier ofcharcoal and the next tip was used.

• Currently, electric soldering irons are used; they consistof coil or ceramic heating elements, which retain heatdifferently, and warm up the mass differently, internal orexternal rheostats, and different power ratings - whichchange how long a bead can be run.

• Common solders for stained glass are mixtures of tinand lead, respectively:60/40 lt b t 361° 376°F




• 60/40: melts between 361°-376°F• 50/50: melts between 368°-421°F• 63/37: melts between 355°-365°F

• lead-free solder (useful in jewelry, eating containers, andother environmental uses): melts around 490°F

Pipe/Mechanical soldering

• Sometimes it is necessary to use solders of different melting pointsin complex jobs, to avoid melting an existing joint while a new joint ismade.

• Copper pipes used for drinking water should be soldered with alead-free solder, which often contains silver. Leaded solder is notallowed for most new construction, though it is easier to create asolid joint with that type of solder. The immediate risks of leadedsolder are minimal, since minerals in municipal or well watersupplies almost immediately coat the inside of the pipe, but lead willeventually find its way into the environment.

• Tools required for pipe soldering include a blowtorch (typicallypropane), wire brushes, a suitable solder alloy and an acid pasteflux typically based on zinc chloride Such fluxes should never be




flux, typically based on zinc chloride. Such fluxes should never beused on electronics or with electronics tools, since they will causecorrosion of the delicate electronic part.

Soldering defects• Soldering defects are solder joints that are not soldered correctly.

• These defects may arise when solder temperature is too low.

• When the base metals are too cold, the solder will not flow and will"ball up", without creating the metallurgial bond.

• An incorrect solder type (for eg. electronics solder for mechanical joints or vice versa) will lead to a weak joint.

• An incorrect or missing flux can corrode the metals in the joint.Without flux the joint may not be clean.

• A dirty or contaminated joint leads to a weak bond. A lack of solder ona joint will make the joint fail.

• An excess of solder can create a "solder bridge" which is a shortcircuit. Movement of metals being soldered before the solder has

cooled will make the solder appear grainy and may cause a weakened joint.

• Soldering defects in electronics can lead to short circuits high




• Soldering defects in electronics can lead to short circuits, highresistance in the joint, intermittent connections, componentsoverheating, and damaged circuit boards. Flux left around integratedcircuits' leads will lead to inter-lead leakage.

• It is a big issue on surface mount components and causes improperdevice operation as moisture absorption rises. In mechanical jointsdefects lead to joint failure and corrosion



Brazing

• Is similar to soldering but uses higher meltingtemperature alloys, based on copper, as the filler metal.

• "Hard soldering", or "silver soldering" (performed withhigh-temperature solder containing up to 40% silver) isalso a form of brazing, and involves solders with meltingpoints above 450 C. Even though the term "silversoldering" is more often used than silver brazing, it istechnically incorrect.

• Since lead used in traditional solder alloys is toxic, much








Since lead used in traditional solder alloys is toxic, mucheffort in industry has been directed to adapting solderingtechniques to use lead-free alloys for assembly ofelectronic devices and for potable water supply piping.

Brazing

• Brazing is a joining process whereby a non-ferrous fillermetal and an alloy are heated to melting temperature(above 450°C;) and distributed between two or moreclose-fitting parts by capillary action.

• At its liquid temperature, the molten filler metal interacts

with a thin layer of the base metal, cooling to form anexceptionally strong, sealed joint due to grain structureinteraction. T

• he brazed joint becomes a sandwich of different layers,each metallurgically linked to each other.

• Common brazements are about 1/3 as strong as thematerials they join, because the metals partially dissolveh th t th i t f d ll th i



http://en.wikipedia.org/wiki/Ferrous





http://en.wikipedia.org/wiki/Metallurgy

http://en.wikipedia.org/wiki/Metallurgy






http://en.wikipedia.org/wiki/Ferrous




each other at the interface, and usually the grainstructure and joint alloy is uncontrolled.

• To create high-strength brazes, sometimes a brazement

can be annealed, or cooled at a controlled rate, so thatthe joint's grain structure and alloying is controlled.

• In Braze Welding or Fillet Brazing, a bead offiller material reinforces the joint. A braze-

welded tee joint is shown here.• In another common specific similar usage,

brazing is the use of a bronze or brass filler rodcoated with flux, together with an oxyacetylene

torch, to join pieces of steel. The AmericanWelding Society prefers to use the term BrazeWelding for this process, as capillary attractionis not involved, unlike the prior silver brazingexample.

• Braze welding takes place at the meltingtemperature of the filler (e.g., 870 °C to 980 °C

http://en.wikipedia.org/wiki/Annealing_%28metallurgy%29

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http://en.wikipedia.org/wiki/Bronze



http://en.wikipedia.org/wiki/Oxyacetylene



http://en.wikipedia.org/wiki/Oxyacetylene



http://en.wikipedia.org/wiki/Bronze

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temperature of the filler (e.g., 870 C to 980 Cfor bronze alloys) which is often considerablylower than the melting point of the base material(e.g., 1600 °C for mild steel).

• A variety of alloys of metals, including silver , tin,

zinc, copper and others are used as filler forbrazing processes.

• There are specific brazing alloys and fluxesrecommended, depending on which metals are

to be joined. Metals such as aluminum can bebrazed though aluminum requires more skill andspecial fluxes. It conducts heat much better thansteel and is more prone to oxidation.

• Some metals, such as titanium cannot be brazedbecause they are insoluble with other metals, or

http://en.wikipedia.org/wiki/Silver

http://en.wikipedia.org/wiki/Tin







http://en.wikipedia.org/wiki/Tin

http://en.wikipedia.org/wiki/Silver




yhave an oxide layer that forms too quickly atintersoluble temperatures.

• Although there is a popular belief that brazing isan inferior substitute for welding, this is false.

• For example, brazing brass has a strength andhardness near that of mild steel, and is muchmore corrosion-resistant.

• In some applications, brazing is indisputably

superior. For example, silver brazing is thecustomary method of joining high-reliability,controlled-strength corrosion-resistant pipingsuch as a nuclear submarine's seawater coolantpipes.

• Silver brazed parts can also be preciselymachined after joining, to hide the presence of




ac ed a te jo g, to de t e p ese ce othe joint to all but the most discerning observers,whereas it is nearly impossible to machine weldshaving any residual slag present and still hide

joints.

• In order to work properly, parts must be closely fitted and the basemetals must be exceptionally clean and free of oxides for achievingthe highest strengths for brazed joints.

• For capillary action to be effective, joint clearances of 0.002 to 0.006inch (50 to 150 µm) are recommended. In braze-welding, where a thickbead is deposited, tolerances may be relaxed to 0.5 mm.

• Cleaning of surfaces can be done in several ways. Whichever way isselected, it is vitally important to remove all grease, oils, and paint.For custom jobs and part work, this can often be done with fine sandpaper or steel wool.

• In pure brazing (not braze welding), it is vitally important to use

sufficiently fine abrasive. Coarse abrasive can lead to deep scoringthat interferes with capillary action and final bond strength. Residualparticulates from sanding should be thoroughly cleaned from pieces.




p g g y p

•

• In assembly line work, a "pickling bath" is often used to dissolveoxides chemically. Dilute sulfuric acid is often used. Pickling is also

often employed on metals like aluminum that are particularly prone tooxidation.

• In most cases, flux is required to prevent oxides from formingwhile the metal is heated. The most common fluxes for bronzebrazing are borax-based. T

• he flux can be applied in a number of ways. It can be applied asa paste with a brush directly to the parts to be brazed.Commercial pastes can be purchased or made up from powdercombined with water (or in some cases, alcohol). Alternatively,brazing rods can be heated and then dipped into dry flux

powder to coat them in flux.• Brazing rods can also be purchased with a coating of flux. In

either case, the flux flows into the joint when the rod is appliedto the heated joint. Using a special torch head, special fluxpowders can be blown onto the workpiece using the torch flame

itself.• Excess flux should be removed when the joint is completed.

Fl l ft i th j i t l d t i




Flux left in the joint can lead to corrosion.• During the brazing process, flux may char and adhere to the

work piece. Often this is removed by quenching the still-hot

workpiece in water (to loosen the flux scale), followed by wirebrushing the remainder.

• Brazing is different from welding, where even

higher temperatures are used, the base material melts andthe filler material (if used at all) has the same compositionas the base material.

• Given two joints with the same geometry, brazed jointsare generally not as strong as welded joints. Carefulmatching of joint geometry to the forces acting on the joint, however, can often lead to very strong brazed joints.

• The butt joint is the weakest geometry for tensile forces.The lap joint is much stronger, as it resists throughshearing action rather than tensile pull and its surfacearea is much larger. To get joints roughly equivalent to a

weld, a general rule of thumb is to make the overlap equalto 3 times the thickness of the pieces of metal being






joined.

• The "welding" of cast iron is usually a brazing operation,with a filler rod made chiefly of nickel being used

although true welding with cast iron rods is also available.

• Vacuum brazing is another materials joining technique,one that offers extremely clean, superior, flux free braze joints while

providing high integrity and strength.• The process can be expensive because it is performed inside avacuum chamber vessel however, the advantages are significant.For example, furnace operating temperatures, when usingspecialized vacuum vessels, can reach temperatures of 2400 °C.Other high temperature vacuum furnaces are available ranging from1500 °C and up at a much lesser cost.

• Temperature uniformity is maintained on the work piece whenheating in a vacuum, greatly reducing residual stresses because ofslow heating and cooling cycles.

• This, in turn, can have a significant impact on the thermal andmechanical properties of the material, thus providing unique heattreatment capabilities.

• One such capability is heat treating or age hardening the work piecewhile performing a metal-joining process, all in a single furnaceth l l








thermal cycle.

Reference: M.J.Fletcher, “Vacuum Brazing”. Mills and BoonLim ited: Londo n, 1971.

Advantages over welding

• The lower temperature of brazing and braze-welding is lesslikely to distort the work piece or induce thermal stresses.For example, when large iron castings crack, it is almostalways impractical to repair them with welding. In order toweld cast-iron without recracking it from thermal stress, the

work piece must be hot-soaked to 1600 °F. When a large(more than fifty kilograms (100 lb)) casting cracks in anindustrial setting, heat-soaking it for welding is almostalways impractical. Often the casting only needs to bewatertight, or take mild mechanical stress. Brazing is thepremium, preferred repair method in these cases.

• The lower temperature associated with brazing v/s. weldingcan increase joining speed and reduce fuel gas




j g p gconsumption.

• Brazing can be easier for beginners to learn than welding.• For thin workpieces (e.g., sheet metal or thin-walled pipe)

brazing is less likely to result in burn-through.

• Brazing can also be a cheap and effective techniquefor mass production. Components can be assembledwith preformed plugs of filler material positioned at joints and then heated in a furnace or passedthrough heating stations on an assembly line. Theheated filler then flows into the joints by capillary

action.• Braze-welded joints generally have smoothattractive beads that do not require additionalgrinding or finishing.

• The most common filler materials are gold incolour, but fillers that more closely match the




ycolor of the base materials can be used ifappearance is important.

Possible problems• A brazing operation may cause defects in thebase metal, especially if it is in stress. This canbe due either to the material not being properly

annealed before brazing, or to thermalexpansion stress during heating.• An example of this is the silver brazing of

copper-nickel alloys, where even moderatestress in the base material causes intergranular

penetration by molten filler material duringbrazing, resulting in cracking at the joint.




g, g g j• Any flux residues left after brazing must be

thoroughly removed; otherwise, severe

corrosion may eventually occur.

Brazing processes

• Block Brazing

1584_lnote_welding 2009.ppt

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