aircraft production tech

8/12/2019 Aircraft Production Tech

1/201


2/201

%. What is core 7enting

!hile pouring the mould with molten metal, mould walls and cores heat up rapidly and give off a large

volume of gases. )hese gases must be vented out through core prints in order to prevent casting defects such

as * "low holes *.

8. What is core ba9ing

)o impart proper strength to the cores, these are ba&ed or cured in gas, oil or electric ovens. )he curing

operation drives off the moisture and hardens core binders.

:. Write on the t,o designs of induction furnaces.

(. Core less or high fre+uency induction furnace.

. Core or channel furnace or low fre+uency induction furnace.

1$. +tate the different t"pes of mou)ding machines.

-olt machine

S+ueezer machine

-olts+ueezer machine

Sand slinger etc

11. )assif" the 7arious methods of inspection and testing of castings.

/isual #nspection

'imensional #nspection

Metallurgical Control

Pressure )esting

0adiographical testing

Magnetic testing

Magnetic particle testing

1ddy current #nspection

2ltrasonic testing

12. 4efine manufacturing.

Manufacturing means the ma&ing of goods and articles by hand and or by machinery.

1'. 4efine manufacturing ngineering.

Manufacturing 1ngineering can be defined as the study of the various processes re+uired to reproduce

0( T3 4r. RR 5 4r. +R T3NIA( UNI0R+IT6


3/201

parts and assemble these into machines and mechanism.

1*. )assif" the manufacturing processes.

Casting processes

'eformation processes

Machining processes

Powder metallurgy

-oining processes

eat treatment and surface treatment process

1-. What is meant b" )ost#,a; method

)his method involves the use of e%pandable pattern surrounded with a shell of refractory material to

form the casting mould. Casting is formed by pouring the molten metal in the mould cavities created by

melting out the pattern. Since the pattern made of wa% is melted out and gets destroyed, that is why the name

lostwa% method.

1/. Write the ad7antages and disad7antages of )ost#,a; method.

Ad7antages . Carbon pic& up in the case of steels.

11. 4iscuss the 7arious Inspection methods to defects in castings.

)he various inspection and testing procedures may be classed as follows

1. 0isua) Inspection

/isual inspection of castings can reveal many of the common surface defects such as misrun, crac&s

and warping etc. )his method is very common and is applicable both in piece and mass production of

castings. )he inspection is carried out in two steps prior to cleaning and annealing and then after the final

finishing operation.

2. 4imensiona) Inspection


G


29/201

$eometric dimensions of castings are chec&ed by means of measuring tools such as plug and snap

gauges, template gauges, mar&ed out plates and special alliances, to establish whether the dimensions of the

casting conform to the drawing or not and to ma&e certain that the pattern and core bo%es are correct. )he

deviations of dimensions should not e%ceed the permissible limits.

'. !eta))urgica) ontro)

2nder this the chemical composition and the mechanical and other properties are determined in a

laboratory.

)he chemical composition of castings is chec&ed by the methods of chemical and spectral analysis.

9or this, the test pieces are commonly cast on test bars, that is, cast integral with the casting, or separately

cast test specimens prepared for chec&ing strength properties.

)he strength or mechanical tests include test in bending, tension, hardness, compression shear and

creep.

*. Pressure Testing

)his test is carried out on those castings to be used for conveying li+uids or gases. )he castings are

chec&ed for pressure tightness or impermeability and lea&age. )he tests include water or air pressure tests.

#n water pressure test, the casting is held under a certain pressure of water, the test pressure depends

on the conditions under which the casting has to function. )he outer surface of the casting must be dry,

otherwise it will not be possible to detect the traces of lea&age, if any.

#n the air pressure test, a soap solution is applied to the surface of the casting. !hen the casting is

subHected to air pressure testing, bubbles will appear on the surface showing the place of lea&age, if any.

-. Radio graphica) Testing

#nternal defects in a casting such as crac&s, voids, cavities and porosity etc., as well as surface crac&scan be revealed by radiographic inspection using %rays and rays.


I


30/201

#n %ray testing ;figure< short wave length rays from an %ray tube are passed through a casting andrecorded on a special film held against the opposite face of the casting. #f the casting has an internal defect,

the density of the material at that spot will be less as compared to the surrounding material. )his area will

allow more penetration of the rays, that is, the sections of the casting with crac&s cavities will absorb a

smaller amount of %rays as compared to fully dense material. )his will result in the appearance of a dar&

shadow on the %ray tube is a high voltage source 66 &/ for casting thic&ness upto 76 mm and ( million

volts for thic&ness form 76 to (G6 mm.

ray testing is used for chec&ing heavy walled casings since these rays are more penetrating and less

scattering as compared to %rays. ray radiate from 0adium or its salts contained in a capsule. Another

source can be radio active element CoD6.

/. !agnetic Testing

#n this method, the casting to be tested is magnetized and then place between the poles of an

electromagnet or in the magnetic field of a solenoid coil. )he energized coil is now moved along the casing.

#f the coil comes across a defect on its way, the magnetic flu% changes its direction and induces an emf in

the coil turns, the value of which shows up on the galvanometer.

)he method can detect defects ;crac&s< on the surface or slightly below the surface of a casting.

)hus, it supplements the radiographical methods which ordinarily can not detect small crac&s. owever, the

method can be applied to castings made from ferromagnetic metals.


46


31/201

%. !agnetic Partic)e testing

)his method of inspection is a procedure used to determine the presence of defects at or near the

surface of ferromagnetic castings.

)he method is based on the principle that, if an obHect is magnetized, surface crac&s and voids in the

material, which are at an angle to the magnetic lines of force, interrupts the magnetic field which gets

distorted. )hat is, there is an abrupt change in the path of a magnetic flu% lea&age field and hence

interference with the magnetic lines of force. )he magnetic lines spread out in order to detour around the

interruptions, figure. )his interference is detected and hence the shape and size of the crac& or void isrevealed, by the application of a fine powder of magnetic material, which tends to pile up around and bridge

over the discontinuities. A surface crac& is indicated by a line of the fine particles following the outline of

the crac&.

)he magnetic powder may consist of fine iron filings, but 9eB4is preferred which is ground to pass

a (66mesh sieve. A variation of the method is that the magnetic particles are prepared with a fluorescent

coating. #nspection will be carried out under 2./. light to intensify the effect. 1very crac& will be mar&ed

by a glowing indication.

!hen the plain magnetic powder is used, the trade name of the method is *Magnaflu%, but when

magnetic particles with a fluorescent coating are used, the method is called *Magnaflow or *Magnaglo.

)he powder may be applied dry or wet. 9or the dry method, the powder is applied in the form of a

cloud or spray. #n the wet method, the powder is suspended in a low viscosity, noncorrosive fluid such as

&erosene oil ;(66 g of magnetic powder in about 7( of 3.oil


32/201

which is supplied with a high fre+uency current. #t induces an electric field in the casting. )he field

changes in the presence of surface or near surface defects. )hese changes show up on instruments.

:. (iquid penetrant Inspection

)his method can reveal surface defects only but can be used for any material. )he surface of thecasting is thoroughly cleaned and dried. )hen the li+uid penetrants are applied as sprays or by immersion.

)he penetrant li+uid contains either a material which will fluoresce under blac& light or a dye that can be

visually detected. )he li+uid penetrant will be readily drawn into e%tremely small surface crac&s. )he

surface is cleaned and dried. )hen, a powder material called a *developer is sprayed on the surface. )he

penetrant trapped in defects bleeds out due to blotting action and delineate defects during development. )he

penetrant e%tent of the discontinuity in the casting surface will be proportional to the amount of penetrant

bleeding out. #f a fluorescent penetrant is used, defects show up as glowing yellow green dots or lines

against a dar& bac& ground. #n dye penetrants, defects are revealed as red dots or lines against a white

bac&ground.

1-. ;p)ain the different t"pes of pattern materia)s and their ad7antages and disad7antages.

a& Wood. )he wood used for pattern ma&ing should be properly dried and seasoned. #t should not contain

more than (6@ moisture to avoid warping and distortion during subse+uent drying. #t should be straight

grained and free form &nots.

Ad7antages

(. Light in weight.

. Comparatively ine%pensive.

4. $ood wor&ability

>. Lends itself to gluing and Hoining.


4


33/201

7. olds well varnishes and paints.

D. Can be repaired easily.

(imitations

(. #nherently non uniform in structure.

. Posses poor wear and abrasion resistance.

4. Cannot withstand rough handling.

>. Absorbs and gives off moisture, so that it varies in volume, warps and thus changes its mechanical

properties. )hese drawbac&s, however, can be remedied by drying and seasoning it and then giving

coats of water proof varnishes and paints.

)he following types of wood are commonly used for pattern ma&ing

;i< White Pine. #t is the most widely used wood, because of its straight grain and light weight and

because it is soft, easy to wor& and unli&ely to wrap.

;ii< !ahogan". #t is harder and more durable than white pins. Can be wor&ed easily if straight

grained. #t is less li&ely to warp than some of other woods.

;iii< !ap)e@ =irch and herr".)hese woods are harder and heavier than white pine. )hey tend to

warp in large sections, so should be used for small patterns only. )hey should be carefully

treated, because, they pic& up moisture readily.

)he outer common wood materials are )ea&, Shisham, 3ail and 'eodar.

;b< !eta). A metal pattern can be either cast from a master wooden pattern or may be machined by the usual

methods of machining. Metal patterns are usually used in machine moulding.

Ad7antages.

(. More durable and accurate in size than wooden patterns

. ave a smooth surface.

4. 'o not deform in storage.

>. Are resistant to wear, abrasion. Corrosion and swelling.7. Can withstand rough handling.

(imitations.

(. 1%pensive as compared to wood.

. =ot easily repaired.

4. eavier than wooden patterns.

>. 9errous patterns can get rusted.

)he common metals used for pattern ma&ing are


44


34/201

;i< .I. !ith fine grain can be used as a pattern material. #t has low corrosion resistance unless

protected eavier and difficult to wor& owever, it is cheaper and more durable than other

metals.

;ii< =rass.May be easily wor&ed and built up by soldering or brazing. #t has a smooth, closed pore

structure. #t is e%pensive, therefore, generally used for small cast parts.

;iii< A)uminium.#t is the best pattern material, because it is easily wor&ed, light in weight and is

corrosion resistant. #t is however, subHect to shrin&age and wears by abrasive action.

;iv< White !eta). #thas low shrin&age, can be cast easily, has low melting point, is light in weight

and may be built up by soldering. owever, it is subHect to wear by abrasive action of sand.

;C< P)astics. )he use of plastics for pattern material results in following advantages

(. 9acilitates the production process.

. Ma&es it more economical in cost and labour

4. Plastic patterns are highly resistance to corrosion, lighter and stronger than wood patterns.

>. Moulding sand stic&s less to plastics than to wood

7. =o moisture absorption

D. Smooth surface of patterns.

:. Strong and dimensionally stable.

/arious plastic ma&e good materials for the production of patterns. )hese are the compositions based on

epo%y, phenol formaldehyde and polyester resinsJ polyacrylates, polyethylene, polyvinylchloride, and

others. #n most wide use are cold curing plastics based on epo%y resins and acrylates.

Plastics patterns are made by one of the following methods

;i< "y inHecting a plastic material into a die.

;ii< 2tilizing laminated construction by building up successive layers of resin and glass fibre.

;iii< "y Pouring a plastic material into a plaster mould.

1/. ;p)ain the sequence of operations performed in ma9ing of a sand mou)d.

)he se+uence of operations performed in the ma&ing of a sand mould is outlined below. 9or this, agreen sand mould and a split pattern have been chosen.

)he appropriate split pattern is made which is split into two e+ual parts at the parting plane and

Hoined together with dowel pins. !e will use a two flas& system, fig.

A. 3and !ou)ding Process.

(. )he drag half of the pattern, that is, the half with dowel holes rather than dowel pins, is placed with

the flat parting plane on a flat board called *Moulding board.

. )he drag is placed over the moulding board with the alignment or locating pins downwards.


4>


35/201

4. A parting material is dusted over the pattern and the moulding board to facilitate both the removal of

the pattern from the mould and the separation of the two mould halves.

>. )he drag is filled with moulding sand and it is pac&ed and rammed around the pattern. )he ramming

is done manually with hands and with hand rammers ;wooden or iron


36/201

(. A pouring basin is cut adHacent to the sprue and then the sprue and riser pins are with drawn.

(4. )he cope is carefully lifted off the temporally separated from the drag and placed on one side.

(>. )o ta&e out the split pattern from the drag, *draw spi&es are drawn into the pattern and the pattern is

loosened from the send by rapping them lightly in all directions with a wooden hammer called a

*mallet. )hen the pattern is lifted off with the help of draw spi&e. "efore with drawing the pattern,

the sand around it is moistened with a *Swab so that the edges of the mould remain firm when the

pattern is withdrawn.

(7. )he gate and runner are cut in the drag or both cope and drag, connecting the mould cavity and the

sprue opening. Sometimes, the gate and runner are automatically made with the help of e%tensions

on the pattern. #f needed, all the cavity edges are repaired. 'irt remaining in the mould cavity is

blown off with a stream of air. #f cores are to be used, they are properly placed in position in thedrag.

(D. )he mould is now assembled, the cope being carefully placed over the drag so that the locating pins

fit into the holes.

(:. #f the lifting force on the cope due to the hydraulic pressure of the molten metal is greater than the

weight of the cope, the cope must either be clamped to the drag or else weights must be placed on the

top of the cope.

(G. )he mould is now ready for pouring.

1%. ;p)ain an" t,o t"pes of mo)ten meta) inGection mechanism for die casting machines.

Digure< +ubmerged P)unger !achine

1. +ubmerged P)unger !achine

9igure shows the submerged plunger type hot chamber machine. )he ram or plunger is submerged

below the surface of the molten metal, and operates with in a cylinder. )he wor&ing medium can be

pneumatic or hydraulic. )he casting cycle consists of the steps already e%plained. )he dies are loc&ed


4D


37/201


38/201

4efinition. A core is a body made of refractory material ;sand or metal, metal cores being less fre+uently

used


39/201


40/201

i7& 3anging ore

N9igure ;d


41/201

;C< Pouring =asin. #t is a reservoir at the top of the sprue ;in cope< that receives the stream of molten metal

poured from the ladle.

;d< +prue. A sprue or down gate is a vertical channel that connects the pouring basin with runners and gates.

#t is made somewhat tapered downward for case of moulding and more importantly to have a decreasing

crosssectional area corresponding to the increase in velocity of the molten metal as it flows down the sprue

hole. )his prevents turbulents flow and hence the drawing in or air along with the li+uid into the mould

cavity.

;e< +prue base or ,e)). #t is a reservoir at the bottom end of the sprue. #t prevents e%cessive sand erosionwhen the molten metal stri&es the runner at the sprue base. Also, there is considerable loss of velocity in the

well.

;f< Runner. )he runner is generally a horizontal channel whose functions are to trap slag and connect the

sprue base with the gates ;ingates


42/201

combination with water, it is the bonding agent in green sand. Although moist sand particles do adhere to

one another slightly, but coating with moist clay, the strength ;tensile and shear< of the sand mi% is increased

about threefold. Clay imparts cohesiveness and plasticity to the moulding sand in the most state and

increases its strength after drying. !hen the moulding sand has the proper amount of water added to it to

give a high strength with sufficient plasticity, the sand is said to be *at temper or *tempered.

Additives impart to the moulding sand special properties ;strength, thermal stability, permeability,

refractoriness, thermal e%pansion etc.. Strong sand 2pto 46@ clay

7. 1%tra Strong sand ;Loam sand@ for lean sands and of D to :@

for loam sands.

A typical green moulding sand for gray iron moulding are given below


>


43/201

Silica sand F DG to GD@

Clay F (6 to 6@

!ater F 4 to D@

Additives F (to D@

=inders. "inders used in a foundary are #norganic and organic binders. Brganic binders are mainly used for

core ma&ing and will be discussed later.

Clay binders are the most common inorganic binders. Clays are formed by the weathering and

decomposition of roc&s. )he common types of clay used in moulding sand are 9ireclay, &aolinite, little and

"entonite. 3aolinite and "entonite clays are most popular, because, they have high thermochemicalstability.

1. Dire#c)a". 9ire clay is a refractory clay usually found in the coal measures.

2. Hao)inite.#ts general composition is A#B4.SiB.B. #t is one of the decomposition products of

the slow weathering of the granite and basalt ; a &ind of blac& roc&


44/201

UNIT II

W(4IN AN4 +3T !TA( DBR!IN

PART A

1. 4efine ,e)ding.

!elding is defined as an localised coalescene of metals, where in coalescence is obtained by heatingto suitable temperature, with or without the application of pressure and with or without the use of filler

metal.

2. )assif" the different ,e)ding processes.


>>

Welding

Fusion Welding Brazing & Soldering Solid StateWelding

Chemical Electrical Electrical Chemical

Resistance DiffusionE!osion

"echanical

Cold Friction#ltrasonic

$%fuel gashermit

'rcResistance

Electrical Beam(aser Beam


45/201

'. 4efine gas ,e)ding.

$as welding is a group of welding processes where in coalescence is produced by heating with a

flame or flames with or without the application of pressure and with or without the use of filler material.

*. 4ifferentiate bet,een Autogeneous@ 3omogeneous an 3etro#geneous ,e)ding process.

Auto eneous ,e)ding processes . Spinning

*'. (ist the 7arious maGor shearing operations in sheet meta)

(. Shearing

. "ending

4. 'rawing and

>. S+ueezing

**. What is meant b" c)earance

Clearance is the intentional space between the punch cutting edge and the die cutting edge. 'epends

on the type of cutting operation, the space between punch and die is provided &nown as clearance.

*-. The meta) is stressed KKKKKKKK in bending operations

"eyond the elastic limit.

*/. !ention the effect of insufficient c)earance

#t does not allow a clean brea& but partial brea& occurs. #t is also called as secondary shear.

*%. What is meant b" seaming


7>


55/201

)he process of providing loc& between the two edges of the different wor& metal is called as

seaming.

*8. +tate the ad7antages of press ,or9ing operations

Material economy,

0eduction of weight and considerable cost reduction of fabricated parts,

igh productivity,

2se of uns&illed labour, igh degree of precision,

2niformity of parts,

*:. 3o, deep dra,ing operations differ from sha))o, dra,ing operations

)he length of the part to be drawn is deeper than its width.

-$. What is stretching

Stretching is the process of stressing the wor& blan& beyond its elastic limit by moving a form

towards the blan& or sheet metal.

-1. 4efine the term Lspring bac9M.

Spring bac& is defined as the movement of the metal to resume its original position causing a

decrease in bend angle after the applied force is withdrawn.

-2. +tate the methods of stretch forming process

(. 9ormbloc& method

. Matingdie method

-'. 3o, force e;erted on the form b)oc9 is ca)cu)ated

!hen the formbloc& moves towards the blan&, the hydraulic fluid inside cylinder gets compressed

and delivered through the outlet valve. )he movement of the form always depends the hydraulic fluid

pressure inside cylinder. )he fluid is entered the cylinder when the formbloc& moves away from the blan&

after completing stretching process. #n one stretching process, we can get no need of stages in stretching.

9orce e%erted on the piston is calculated as

,

>F d p

=

!here, d F 'iameter of the piston


77


56/201

p F ydraulic fluid pressure

-*. What are the ad7antages of stretch forming operations

(. "lan&s can be stretched in a single operation.

. =o need of any heattreatments before and after the stretching process.

4. Spring bac& is reduced or eliminated when compared to other forming methods.

>. 'irect bending is not introduced.

--. (ist out the app)ications of stretch forming operations

(. Production of aircraft wing and fuselage parts.

. Production of contoured panels for truc& trailer and bus bodies in automobile industry.

-/. !ention the 7arious materia)s used for ma9ing dies and form b)oc9s in stretch forming process

!ood,

Masonite,

Kinc alloys and

Cast iron.

-%. +tate the )a, of process of fracturing in formabi)it"

)he ductility of the same material is lower if the section size is larger.

-8. +tate the )a, of geometrica) simi)itude

(. "lan&s are geometrically similar in all aspects with respect to another blan& such as dimension,

thic&ness, width, length etc. )hese geometrically similar blan&s should ne fabricated by using

similar tools.

. 2nit strains at corresponding locations are identical for geometrically similar blan&s.4. )he forces re+uired to form any re+uired shape on geometrically similar blan&s are directly

proportional to the s+uare of the thic&ness.

>. )he consumption of wor& for forming the re+uired shape is also proportional to the cube of its

thic&ness for geometrically similar blan&s.

-:. What are the formabi)it" test methods

(. 9ormability tests for bul& deformation.

. 9ormability test for elasticplastic deformation and

4. Simulative tests for forming operation.

>. 9ull scale forming tests.


7D


57/201

/$. 3o, ,or9#hardening is predicted in terms of stress#strain in formabi)it"

2sually, the strain distribution in assessed from the surface, but, the magnitude of strain is

determined by impregnating the sheet metal with a grid pattern or concentric circles followed by presenting.

'uring pressing of sheet metal, concentric circles are stretched into elliptic during pressing the sheet metal.

)he maHor and minor a%es of ellipse give the directions of principal strains.

/1. !ention the 7arious t"pes of simu)ati7e tests carried out for 7arious cup forming process

(. 1richson test. Blsen test

4. Surift test

>. 9u&ui test.

/2. Dro accessing the stretchabi)it" of the sheet meta)@ ########## test are carried out.

(. 1richson test

. Blsen test

/'. (4R refers to ##########

Limiting 'rawing 0atio

/*. Dur9ui test is carried out for accessing both dra,abi)it" and stretchabi)it". +a" true or fa)se.

)rue.

/-. What are the app)ications of forming )imit diagram

(. )he new set of tools in easy, hard or impossible to wor& can be easily determined.

. $ood materials used in forming operations are identified.

4. Location of source of trouble is also easy from a reference pressing by the designer.

//. 3o, specia) forming process is defined

#n the case of mating die method, sheet metal is placed over the lower die and its ends are fi%ed on

movable grippers. )hen, the upper die is moved towards the blan&. #f the female or upper die is actuated by

any other means e%cept hydraulic fluid contained in the cylinder in forming process called special forming

process.

/%. What are the t"pes of specia) forming process

(. ydroforming

. 0ubber pad forming


7:


58/201

4. Metal spinning

>. 1%plosive forming

7. Magnetic pulse forming

D. Peen forming

:. Super plastic forming

/8. What are the ad7antages of h"droforming process

(. )hinning of metal, spot stresses and spring bac& are drastically reduced or completely eliminated.

. #t is used for mass production because wor& performed per operation is high.

4. )ool changing can be done rapidly.

>. Complicated contours can also be made.7. Sharp corners are also possible.

D. All type of sheet metals can be handled.

/:. Rubber pad forming process is a)so 9no,n as ##########

0ubber pad forming process is also called as marform process.

%$. 3o, upper die is pressed against the sheet meta) surface in rubber pad forming process

9irst, the blan& is placed over the punch called male die. )hen, the upper platen called female part is

moved to Hust touch the top surface of the wor&. After this, the force is applied and gradually increased on

the blan& through the rubber pad.

%1. +tate the )imitations and app)ications of rubber pad forming processQ

(imitations(I, :>:766C. 1lectrodes are made of coldrolled electrolytic copper with some Cd,Cr, or "e additions, or copper E tungsten or molybdenum alloys. 1lectrodes are usually of hollow

construction and are cooled with water during operation to prevent their overheating.

"ecause of the widespread application of sheet metal parts, resistance spot welding finds e%tensive

application in the aircraft and automobile industries for manufacturing air frames and bodies ;there are some

G666 to (6,666 spot welds per car mm thic& for aluminium mm, for t 4 mm

F (.7 t ? 7 mm, for t T 4 mm

where t F )hic&ness of parts being welded.

;b< Spacing of spot welds F 4d.


:6


71/201

8. ;p)ain Resistance +eam We)ding Process in detai) ,ith neat s9etch.

Resistance +eam We)ding@ R+W&< )o obtain a series of spot welds along a line by the 0S! method, an

interrupted wor& movement will be necessary. )he same result can be achieved much more conveniently

and rapidly in the resistance seam welding where the electrodes are in the form of rotating disc electrodes,

with the wor&ing being welded moving continuously by the electrodes, ;figure


72/201

:. ;p)ain the )ectric Resistance =utt We)ding process in detai).

)ectric Resistance =utt We)ding< )here are two types of electric resistance butt welding processes the

upset and the flash.

;i< Upset We)ding@ UW&< #n this process, the ends of the two parts to be Hoined together are

clamped in position in the electrodes. )he movable head is moved towards the fi%ed head until

the abutting surfaces of the wor& pieces are in light contact. )hen the proper current is made to

flow across the interface for a preset time, while the light pressure between the two parts is

maintained. !hen the interface has been heated to the welding temperature ;plastic state


73/201


74/201

)he current densities range from 466 E G66 A 8 cmand the welding voltage is from 7 to (7 /. )he

welding pressure may range from 476 to (>66 MPa.

#n accordance with their capacity and purpose, butt welding machines may be either handoperated

or automatic. )he latter type clamps the parts to be welded and apply pressure for upsetting by mechanical,

hydraulic or pneumatic means, and the process is controlled automatically.

#n the mechanical system, the movable head is moved towards the fi%ed head by means of a cam drive.

)he upset metal is usually removed by subse+uent rolling or grindling.

1$. What is Driction ,e)ding ;p)ain the Princip)e in7o)7ed in it. What are the ad7antages anddisad7antages of the process.

Driction We)ding DRW&< 9riction welding is defined as *A solid state welding process wherein

coalescence is produced by heat obtained from mechanically induced sliding motion between rubbing

surfaces. )he parts are held together under pressure. Bne part is rotated at relatively high speeds and under

pressure against the second part which is held stationary. )he frictional wor& at the contacting surfaces is

transformed into heat. )he contacting surfaces are thus heated to a high temperature below the melding

temperature. At this point, the relative motion between the two is stopped. )he weld is then completed ;by

upsetting< due to the pressure which still continues or additional pressure may be necessary, ;9igure6 MPa. 0elative motion is stopped by

;i< a bra&ing system to the machine spindle.

;ii< an arrangement which releases the stationary part to permit the two parts to rotate together.

Digure< Driction ,e)ding

!eld time is relatively short ;fraction of a second to a few seconds


75/201

)he method is most suitable for circular parts, that is, butt welding of round bars or tubes. Also

welding of a round part output a flat part, for e%ample, stud welding. )he heat zone being very thin,

therefore, dissimilar metals are easily Hoined, for e%ample, aluminium to steel, copper to steel, copper to

aluminium, Aluminium to brass, and mild steel shan&s to high speed steel tools. )he rotational speed is

proportional to thermal conductivity of the metal. )he method is limited to smaller components.

"esides the advantages of the process given above, it also has the following additional advantages

(. Low initial capital cost.. Lowcost power re+uirements.

4. )he process is clean.

>. igh +uality welds.

7. Annealing of weld zone is not necessary.

D. /ery little loss of material through e%clusions.

:. )he process welds the whole surface of contact, unli&e BA! and arc welding which weld only

round the periphery.

9or welding a round bar to a flat plate, the thic&ness of the plate should not e%ceed one +uarter of the bar

diameter. )his combination of dimensions provides an e+ual balance of heat.

)he high +uality of welds obtained by 90! is due to the following factors

;i< As the surfaces rub against each other, all o%ide and adsorbed films and foreign particles are

removed into flash, because the metal is deformed in radial directions. Also, no o%ides are

formed during welding due to the intimate contact between the rubbing surfaces.

;ii< )he metal at the Hoint and in the heataffected area ac+uires a structure having e+uia%ial and fine

grains.

Product app)ications. )he components successfully produced include .S.S. )wist drills, flanges upto (7

cm diameter pipes, gas turbine shafts, Aeroengine drive shafts and valves, refrigerator tubes of dissimilar

metals, hydraulic tubes, steering columns, welding of sintered products, and sulphur E bearing steels.

11. 4efine )ectron =eam We)ding. ;p)ain the ,or9ing princip)e in7o)7ed in it@ the ad7antages and

disad7antages

)ectron =eam We)ding =W&< 1"! can be defined as *A welding process wherein coalescence is

produced by the heat obtained from a concentrated beam composed primarily of high velocity electrons

impinging upon the Hoint to be welded. )he &inetic energy of the electrons is changed into heat on impact


:7


76/201

with wor&, giving intense local heating.

Digure< )ectron =eam We)ding.

)he electron beam is produced in a high vacuum environment by an electron gun, usually consisting

of a tungsten or tantalum cathode, a grid or forming electrode and an anode. A stream of electrons is given

off from a tungsten filament heated to about 66C, ;9igure


77/201

;a< to prevent the tungsten filament of gun from o%idising.

;b< it prevents the electrons from colliding with molecules of air and becoming scattered, with a loss of

power.

;c< enables the welding to be done in a very pure atmosphere eliminating the need for a shielding gas.

Bther ad7antages of =W are6 for welding magnesium which is highly

o%idising and whose o%ides have a much higher melting point than the parent metal. =ow the method has

developed as a means for welding a wide range of other materials aluminium and its alloys, stainless steel,

cast iron, silicon bronze, titanium, =ic&el, copper and carbon steels. )he method is especially suitable for

welding thinner metals ;below D mm


88/201

Digure< D)u; ored Arc We)ding.

a& +e)f shie)ding< ere, the shielding is provided as the flu% burns and produces protective gas, ;9igure


89/201


90/201

ma&es it unsafe. Low pressure blow pipe is e%pensive than the high pressure blow pipe, because the whole

head containing both the nozzle ;tip< and inHector is to be replaced with every nozzle change.

Digure < =)o, Pipes.

-. NoCC)e or Tip< )he nozzle is a device screwed to the end of the blow pipe. #t is used to permit the flow of

o%yacetylene gas mi%ture from the mi%ing chamber of blow pipe to the tip of the nozzle to facilitate burning.

#n order to vary the size of flame ;and heat supply< necessary to weld varying thic&ness of metal, a selection

of tips is available for the blow pipe. 9or this, the nozzles are interchangeable so that the correct nozzle is

fitted at the end of the blow pipe. 1ach nozzle is mar&ed showing its gas consumption in litres8hour and a

table supplied with the blowpipe shows which tip should be used to weld any re+uired thic&ness of metal.

)he delivery pressure from the regulator must be varied according to the sized of the tip used, and

instructions are supplied to obtain the correct conditions.

/. 3ose and 3ose fittings


91/201

flame and molten metal in the weld pool..

21. 4escribe the sheet meta) characteristics.

)he each and every sheet metal processes are having different characteristics as follows

1. Ro)) forming

Long parts with constant comple% cross sections, good surface finish high production rates high

tooling costs are produced.

2. +tretch forming

Large parts with shallow contours suitable for low+uantity production, high labor costs, tooling and

e+uipment costs depend on part size are produced.

'. 4ra,ing

Shallow or deep parts with relatively simply shapes, high production rates, high66 tooling and

e+uipment costs are produced.

*. +tamping

#t includes a variety of operations, such as punching, blan&ing embossing, bending, flanging and

coining, simple or comple% shapes formed at high production rates tooling and e+uipment costs can be high,

but labour cost is low.

-. Rubber forming

#t includes drawing and embossing of simple or comple% shapes, sheet surface protected by rubber

membranes, fle%ibility of operation, low tooling costs.

/. +pinning

Small or large a%isymmetric parts, good surface finish, low tooling costs, but labor costs can be high

unless operations are automated.

+uper p)astic forming

Comple% shapes, fine detail and close tolerances, forming times are long. ence production rates are

low. So, parts are not suitable for high temperature use.


I(


92/201


93/201

2se of less labour.

Possibility of automation.

Wor9ing princip)e of press

Digure< A sing)e side f)" press.

9ly press is manually operated having a cast iron frame. )he screw provided at the top of the frame

is moved in a nut. )he arm and the screw are rotated by the handle. )he punch is connected at the bottom

of the ram and die is tightly fi%ed at the press plates, called bolster. )he support two cast iron weights act as

a energy storage device. An improved and heavier form of fly press, called a double side press. )he main

difference in this type is that the arm and weights are replaced by a heavy flywheel.

7& ushion(I, :>:7. Perfectly s+uare corners cannot be made by 1'M.

2*. What are the ad7antages of !

(. 1CM is simple, fast and versatile method.

. )he metal removal is entirely by metallic ion e%change and so there are no cutting forces and the

wor&piece is left in an undisturbed, stress free state. #t is never subHected to high temperatures or

stresses. Also, due to the absence of cutting forces very thin selections can be machined. Again,

there will be no residual stresses in the wor&piece as a result of the operation.

4. #f proper electrolytes are used, there is no tool wear at all.


((D


117/201


118/201

. )he method is +uite cumbersome and the e+uipment is very costly.

4. )he metal removal rate is very low.

>. At the spot where the electron beam stri&es the material, a small amount of recasting and metal

spatter can occur. )his has to be removed afterwards by abrasive cleaning.

28. What are the ad7antages of (=!

(. =oncontact process with no wor&piece distortion.

. Minimum heat affected zone.

4. Precise operation.

>. igh production rates.

7. Process can be easily automated.

D. #naccessible areas for conventional methods can be processed.

:. ardness of the material does not affect the process.

G. Multiple holes or welds possible in one e%posure.

I. 'issimilar materials can be welded.


((G


119/201

PART =

1. ;p)ain Abrasi7e Eet !achining ,ith necessar" diagram.

Abrasi7e Eet !achining AE!&

#n abrasive et machining method, the material is removed form the surface or a !or&piece, by

impinging a focused Het of fine abrasive particles carried by a compressed gas which imparts &inetic energy

to the stream of fine abrasives. )he stream leaves through a nozzle at a velocity of the order of 466 m8s and

stri&es the surface of the !or&piece, producing impact loading on it. Severe plastic deformation or micro

crac&s occur is the vicinity of the impact. 'ue to repeated impacts, small chips of material get loosened and

fresh surface gets e%posed to the Het.

)he carrier gas can be air, nitrogen or carbon dio%ide, but never o%ygen. )he air must be filtered to

remove water, oil and other contaminants. =ozzle pressure can range between 6.6 =8mm and 6.G7 =8mm

but is usually about 6.7 =8mmigher pressure results in rapid nozzle wear, low pressure gives slow metal

removal rates.

)o resists abrasion and wear of nozzles, these are made of hard materials such as tungsten carbideand synthetic sapphire. )he useful life of sapphire nozzles is about (6 times that of tungsten carbide nozzles.

)he size of the nozzles are usually.

Tungsten arbide

0ound 6.6(7 to 6.G6 mm diameter

0ectangular 6.6:7 mm 6.76 mm to 6.(:7 mm 4.:7 mm

S+uare 6.D7 mm s+uare

Sapphire nozzles 6.6 to 6.D7 mm diameter are made only round

)he various abrasive materials used ion A-M include aluminium o%ide, silicon carbide, glass powderor beads, dolomite ;calcium magnesium carbonate< and specially prepared sodium bicarbonate. !hen

sodium bicarbonate is used, it must be &ept dry. )he cutting performance will depend upon hardness,

strength, particle size and particle shape of the abrasive. AlB4is a general purpose abrasive and is used in

sizes of (6, 7 and 76 microns. SiC is used for fastest cutting on e%tremely hard materials. #t is used in 7

and 76 microns sizes. 'olomite is used in 66 mesh size for light cleaning and etching. Sodium bicarbonate

is used for e%tra fine cleaning and glass beads ;6.D47 to (.: mm diameter< are used for light polishing and

fine deburring.

#n general, larger sizes are used for rapid removal rate while smaller sizes are used for good surface

finish and precision.


((I


120/201

)he metal removal rate will depend upon the diameter of nozzle, composition of abrasive gas

mi%ture, hardness of abrasive particles and that of the wor&materials, particle size, velocity of Het and

distance of !or&piece from the Het. )he typical metal removal rates vary from 6.6(D to 6.6 cm 48min.

Mas&s defining the machining area are sometimes used to prevent stray cutting. Copper a good all

purpose mas&ing material. $lass gives e%cellent definition but has short life. 0ubber has long life but gives

poor definition.

Application of A-M include abrasive, cutting or cleaning ;for e%ample electrical contacts< ad for

machining semiconductors such as silicon, gallium or germanium, for ma&es holes and slots in glass +uartz

sapphire, mica and ceramics.


(6


121/201

Bther applications are cleaning hard surfaces, deburring, scribing, grooving, polishing and

radiusing. A dimensional tolerance of 6.67 mm can be obtained. Surface finish obtained is in the range of

6.7 to (. m CLA )ypical power input is 6.7 &!, the method is used chiefly to cut materials that are

sensitive to heat damage and thin section of hard materials that chip easily and to cut indicate holes that

would be more difficult to produce by other methods. )he other advantage is its low capital cost.

)he disadvantages of the method are low metal removal rate, possibility of stray cutting, embedding

of abrasive particles in soft !or&piece and dust control re+uirements.

A schematic diagram of A-M is shown in figure. 'ry and filtered ;in this case air< is raised to a high

pressure in the compressor. )he pressurized air flows to the vibrating mi%ing chamber containing abrasivepowder. )he mi%ture of pressurized air and abrasive powder than flows to the nozzle. #t then impinges on

the !or&piece after shooting out of the nozzle e%it. )he pressure regulator regulates. )he gas flow and its

pressure. )he feed rate of abrasive powder is controlled by amplitude or vibrations of the mi%ing chamber.

)he movement of the nozzle towards to !or&piece or vice versa is controlled by a cam mechanism or a

pantograph mechanism.

2. ;p)ain U)trasonic !achining.

U)trasonic !echining U+!&

2ltrasonic machining is a &ind of grinding method. An abrasive slurry is pumped between tool and

wor&, and the tool is given a high fre+uency, low amplitude oscillation which, in turn, transmits a high


((


122/201


123/201

brittle, for e%ample, ceramics, borides, ferrites, carbides, glass, precious stories, hardened steel, cermets and

some super alloys, etc. it is used chiefly for drilling holes, engraving, cavity sin&ing ;carbide wire drawing

dies


124/201

+chematic Arrangement of 4! !ethod

)hus, thousands of spar&discharge occur per second across the gap between tool and wor&, which

result in a local temperature of appro%imately (666C. At each discharge, heat transfer from high

temperature spar& ;plasma< to both tool and wor&, melts, partially vaporizes and partially ionizes the metalin a thin surface layer. )he resulting wor& surface is composed of e%tremely small craters. )he time interval

between the spar& is so short that the heat is unable to conduct into the tool and wor&.

Po,er +upp)ies

Many types of electric circuits are available to provide pulsating '.C. across the wor&piece tool gap.

)he earliest models of 1' Machines were fitted with 0esistanceCapacitance ;0C< rela%ation circuit. #n

this system, a current flowing through a resistor of C, which may be as high as >66 f ;on heavy machines


135/201

)he most commonly used solidstate laser is the ruby laser ;crystalline aluminium o%ide or sapphire.7 &/, current F A.

)he ruby laser wor&s with ma%imum efficiency when &ept at a very low temperature. 9or this, li+uid

nitrogen at (IDC is employed. Bn the other hand, the light flash wor&s best when warm, for this, hot air is

circulated over it. )he vacuum chamber between the ruby crystal and the flash lamp acts as an insulator and

enables the two temperatures ;discusses above< to be maintained. )he flash lamp operates from ( flash every

4 min to ( flashes per minute. )he laser beam energy is applied to the wor&piece in less than 6.66s.

Ad7antages of (=!

(. =oncontact process with no wor&piece distortion.

. Minimum heat affected zone.

4. Precise operation

>. igh production rates

7. Process can be easily automated.

D. #naccessible areas for conventional methods can be processed.

:. ardness of the material does not affect the process.

G. Multiple holes or welds possible in one e%posure.I. 'issimilar materials can be welded.

Product App)ications

L"M is again a *micromachining method which can be used for drilling, scribing, cutting and

shaping. oles as small as 6.667 m in diameter have been produced. #t has got the following drilling

applications holes in rubber baby bottle nipples relief holes in pressure plungsJ holes in nylon buttons, in

aerosol spray nozzles in surgical and hypodermic needlesJ flow holes in oil or gas orifices etc. L"M is

finding increasing use in industrial and nonindustrial fields.


(47


136/201

UNIT I0

PART A

1. Purpose b" 3eat Treatment

Purpose of 3eat Treatment. 2niform corrosion

7. #ntergranular corrosion

D. Stress corrosion

:. 1rosion corrosion

G. 9retting corrosion

18. What are the point of contro) and pre7ention of corrosion

)he various methods by which corrosion can be controlled and prevented are given below

(. Protection by design and fabrication procedure

. Modifying the corrosive environment.

4. Application of inhibitors

>. Cathodic protection

7. Alloying

D. Application of protective coatings.

1:. What are the common corrosi7e agent


(>6


141/201


142/201

(6. Little misalignment in two holes in same plane

2'. 4efine +uper finishing

Super finishing process is a proprietary name given to a micro finishing process that produces a

controlled surface condition on parts which is unobtainable by any other method.

Super finishing is a fine honing operation. Super finishing

;i< Achieves higher surface finish on components,

;ii< 0emoves chatter mar&s,

2*. 4efine buffing

"uffing is a final operation to improve the polish of a metal and to bring out the ma%imum luster.

"uffing is a fre+uent operation prior to plating.

#n buffing, the rubbing action is more gentle than the vigorous and aggressive cutting action

employed in polishing.

"uffing removes negligible amount of metal. )he size of the wor& is changed very little, sometimes,

6.667 to 6.66:7 mm.

"asically, buffing flows or smears the surface metal. #t ta&es the pea&s and flows them into valleys.

)his gives a mirror E li&e polish.

"uffing does not maintain flatness or roundness. #t is used only to obtain very smooth reflective

surfaces.

"uffing is usually confined to the non E ferrous metals, such as aluminum, copper, brass and zinc

alloy die castings, stainless steel, chromium and nic&el plate, etc.

PART =

1. ;p)ain in detai) of honing

3oning. 2niform corrosion

7. #ntergranular corrosion

D. Stress corrosion

:. 1rosion corrosion

G. 9retting corrosion

a)7anic corrosion rivets

should be heated to a temperature of I(6X9 to I46X9, and immediately +uenched in cold water. )hese rivets

develop a greater shear strength than 6(: rivets and are used in locations where e%tra strength is re+uired.

Alloy 6> rivets develop their ma%imum shear strength in ( day after being driven.


(D>


165/201

)he 6(: rivet should be driven within appro%imately ( hour and the 6> rivet within (6 to 6

minutes after heat treating or removal from refrigeration. #f not used within these times, the rivets should be

reheat treated before being refrigerated.

11. ;p)ain enera) +afet" Ru)es

1very organization or group of people re+uires a set of rules for the proper regulation, safety and

protection of the individual who ma&e up the group.

#n formulation of general safety rules and in evaluating the need for and the effectiveness of the

e%isting rules, the following points should be considered.

)he initial points to be though about are than

;i< !hether there is a real need for safety rules. 'oes the employee appreciate its purpose, or he

thin&s that he rules were Hust imposed on him without ade+uate consideration of his personal

feelingsQ

;ii< )he safety rules &eep pace with changing conditions.

;iii< )he safety rules should be such which do not cause inconvenience or annoy the employees. )he

human nature should not be defied.

;iv< )here should not be too many safety rules.

;v< )he safety rules should not be so broad or general in nature than they have no real meaning to

employees.

Bnce the above points are given due consideration in the formation of safety rules and realizing that

the safety rules have a substantial impact on the safety of an individual or the entire wor& force and that a

single violation might place the safety of many employees in Heopardy, the necessary disciplinary action

should be ta&en against those who brea& these rules.

Some of the general safety rules are listed below which have been formulated not as restrictive

measures but as guides to wor&ers and supervisors in their cooperative efforts to prevent accidents.

;i< Smo&ing should be strictly prohibited.

;ii< Acts li&e running, tripping others intentionally, throwing things, directing compressed air at others,

or such acts which may startle or distract other employees should not be tolerated.

;iii< Personal protective e+uipment such as safety glasses and respirators, provided on certain Hobs

because of an indicated need, must be worn.


(D7


166/201


167/201

I. Chromediffusion

(6. Siliconising

((. Anodizing

(. Par&erising

1. 3ot 4ipping< ot dipping coatings can be used for coating signaling point metals such as iron and

steel, zinc, tin, lead and an alloy of lead and tin called terne.

)he coating metal should be of such a composition that it forms an alloy at the interface between the

base metal and the coating. #f the coating does not form an alloy, precoating with a metal which alloys both

with a base and the principal coating can be used.

2. a)7anising. #t is the name given to the coating of zinc by hot dipping. )he +uality of the coating is

directly related to its thic&ness which is measured in gms.8mof surface for all products e%cept sheet

where it is measured in gms.8mof sheets (2 sides).

Heavy coatings of zinc are most easily applied by hot dipping than electrolytically. The purity of

zinc affects its bonding property and the appearance of the coating, and besides that it has no effect. So

here bonding does not matter, lo grades of zinc be used.

!t is mainly used in roofing, ire fencing for gardens, etc., buc"ets an ater cans, steel pipes and for

struggle purposes e#posed to atmosphere.

'. Tin P)ating. Tin plating has a pleasing appearance, good corrosion in resistance and it solders ell.

$opper ire is very often tin%plated to increase its suitability for soldering. This coating is usually

applied by hot dipping before the ire has been dran don to final diameter and the subse&uent

operations dra don the copper and tin coating together.

The various applications of tin plating include tin cans for food, biscuit%tins, "itchen utensils, copper

ire, copper tube used in refrigerator.

*. (ead oating< The lead coatings for hot dipping process contain 2 '2 tin and 2 of antimony, thepresence of hich strengthens the coatings considerably. The coatings used generally are thic"er than

terms but thinner than zinc. To compensate for the dra bac" of poor adhesion of coatings lead has

decided advantage because it does not alloy ith steel. The steel is not embrittled and can be used for

deep draing etc. !t ta"es paints and solders ell. To obtain the best possible adhesion, the steel

must be perfectly cleaned before coating.

*ead coating is cheaper substitutes for terne and it can be used for spinning deep draing

operation.

-. !eta)#c)adding< $ladding is usually performed by attaching plates of relatively thic" metals together

such as by elding and then rolling them don together. The centre core and plating metal retain


(D:


168/201


169/201

+i)iconising< #t is carried out for two hours at above (666 C in a mi%ture of siliconcarbide and

ferrosilicon in an atmosphere of chlorine. )he parts siliconised are very hard and process is carried out for

wear corrosion or heat resistance. A typical application is in valves, valve seats, and guides of internal

combustion engines.

AnodiCing


170/201


171/201

wor&piece will result in error and this horizontal erro ;e< will &eep on increasing as the slope of locating

plane increases and will a minimum F t itself, if the locating plane is vertical. Secondly, the inclined

locating plane results in a wedging action which has tendency to lift the piece.

Digure


175/201

25. What are the differences between surface hardening by diffusion method and thermal method?

The difference beteen surface hardening by diffusion method and thermal method are as follos

"y diffusion method "y thermal method

Surface is hardened R finished by

means of non heat treatment.

Surface of any material is finished and

hardened by means of heat treatment.

2/. 4efine too) design@ Gig and fi;tures

Too) 4esign< Tool design is the process of designing and developing the tools, methods 7 techni&ues

necessary to improve manufacturing efficiency 7 productivity.

Eigs


176/201

PART =

1. What are the important princip)e of Gigs and fi;tures.

)he following are the rule for design of Higs and fi%tures

;i< "efore laying out the Hig and fi%tures, the locating points and the outline of clamping

arrangement must be decided.

;ii< All clamping and binding devices should be as +uic& acting as possible.

;iii< #n selection of locating points, it must be ensured that two component parts of a machine can be

located from corresponding points and surfaces.

;iv< -ig should be made fool proof i.e. , the wor& cant be inserted e%cept in the correct way.

;v< 9or rough casting, some locating points must be made adHustable.

;vi< Clamps must be located such that they will be in the best position to resist the pressure of thecutting tool.

;vii< #f possible, all clamps must be made integral parts of the Hig or fi%ture.

;viii< Complicated clamping arrangement must be avoided which are liable to wear or get out of order.

;i%< All clamps should be placed as nearly as possible opposite some bearing point of the wor& , to

avoid springing.

;%< )he design should be such as to ma&e the Hig and possible, consistent with rigidity and stiffness.

;%i< All corners should be rounded.

;%ii< andles may be provided for easy handling of Higs.

;%iii< 9eet should be provided opposite to all surfaces containing guide bushings in drilling and boring

Higs.

;%iv< All bushing should be placed inside of geometrical figure formed by connecting the points oflocation of the feet.

;%v< Abundant clearance should be provided for chip clearance particularly for rough castings.

;%vi< All locations points should be made visible to the operator when placing the wor& in position. #f

possible, holes may be drilled in Hig body to facilitate operator to watch proper location.

;%vii< oles may be provided for e%it of coolant and chips.

;%viii< Clamping lugs should be located so as to prevent springing of the fi%ture.

;%i%< Small drilling Higs are not clamped to the table, but boring Higs and milling and planning fi%tures,

invariably must be firmly secured to the machine on which they are used.

;%%< 9or accurate wor&, the bushing should support the cutting tool within one diameter of the tool

from the wor&.


(:D


177/201


178/201

specified. #t can be reduced by using all components as simple as possible, using standards

parts, using replaceable parts subHect to wear.

Dig< ;amp)e of good dri)) Gig design

'. ;p)ain brief)" ho, ,or9 pieces are )ocated

Locating elements help in placing the wor&piece in essentially, the same position every time again

and again. )hese provide a reference point from which all sizing or spacing can be accomplished. )hese

establish desired relationship between wor&piece and Hig and fi%ture. )he purpose of the locators is to

restrict the three degrees of freedom of translation and the three degrees of freedom of rotation in order to

provide points of reference. )he surface condition of the wor&piece to be located e%erts a great a great

influence on the form of the locator, e.g. finished surfaces can be located on a plane but a rough surface is

located on a few points of contact as deemed necessary for ability of the part. owever, a plane is generallynot used even though a highly finished and true surface is available as a reference surface because of the

danger of misalignment due to minute chip particle or dust, 2sually parts are located on three points which

form a plane, the introduction of more points though offers greater stability , but may introduce the ris& of

unevenness with the lane formed by three points.

)he type of locator selected for a particular application is largely a function of the shape of the

wor&piece and more particularly the shape of the reference surface. )he various type sof locators are

described below.

;i< dge )ocators


179/201

clearance for chip and burrs which may be present in Hig or fi%ture as a result of previous cutting

operations.

;ii< Pin )ocators< )hese are fre+uently used in applications where holes are used as reference points.

#t is important that the wor&piece be placed over the locating pin,

;iii< 0# )ocator


180/201

large e%tent, determines the form , placement and magnitude of the clamping force employed. #f the entire

top surface is to be machined then a side clamp must be used which e%erts both the horizontal and vertical

forces in order to assure a firm holding action. !or&pieces of fragile nature limit the magnitude of the

clamping force. 0ough surfaces permit the either holddown pins that dig into the wor& or serratedfaced

clamps that gives more positive holding action.

)he various type os clamps commonly used are

;i< Sliding clamps, ;ii< inge clamps, ;iii< Camactuated clamps, ;iv


181/201

important that screws should not be used to perform double function of locating and holding.

!here several pieces are to be placed in a fi%ture or Hig, they should be located independently

and not against the other.

;iv< Wear #t further adds to variations. As far as possible, wearresistant materials should be

used for parts subHect to wear on fi%tures Hig, etc. #n the design , wearing surfaces should be

&ept as small as possible without sacrificing too much durability. !ear consideration

demands bigger locating surfaces but locating surfaces should have small area which results

in advantages of less time for cleaning, reduced change of lodgment of chips or dirt,

providing more realistic approach to the mean plane of a rough surface, saving in material

and labour . Sliding over the locators during clamping should be avoided. As far as possible,

provisions must be made to overcome variations due to wear. )he wear allowance is madeon gauges also.

;v< 4ef)ection./ariations in materials, speeds and feeds bring about changes in deflection which

results in varaiation of wor&pieces. 'eflection cannot be eliminated but it can be reduced to

minor proportions to obtain wor&piece dimension within tolerance. 9orces causing deflection

may come from handling, clamping or cutting action. Positive measure must be ta&en to

protect against deflection. 9or this purpose, claps should rever be applied on an

overchanging section of the wor&piece and should bear directly over fi%ed locating resets or

stops. Btherwise the clamping forces should be opposed by adHustable supports. )he devices

employed as reinforcements against deflection themselves should not introduce additional

supports. )he device employed provide ade+uate provisions to limit operator from applying

e%cessive force in applying the support. Supports should be designed to directly oppose the

forces. Ade+uate holding devices should be arranged so that deflection including forces are

transmitted to rigid basic members. All clamping strain should be ta&en care of within a

fi%ture and not transmitted to the table of the machine.

;vi< Therma) e;pansion. #t can affect variations and occurs due to heat generated during cutting

operation. #t effect is more pronounced when two dissimilar metals are involved. )he

temperature differential should be minimized by adopting sharp tools of proper shape,

including provisions for heat dissipitation from tools and machine and employing and

employing controlled room temperature.

;vii< 4irt@ chips and burrs.)hese directly interfere with wor&piece location, positioning and

gauging. 9or this, sharp corners should be avoided between locating surface as they catchdust and are hard to clean. Locating surface should be free for cleaning purpose.

;viii< 3uman deficiencies. Many devices have been developed to multigate the effects of human

deficiencies. -igs and fi%tures should be designed to provide means of achieving desired

accuracy with least s&ill and effort on part of operator.

%. a& What is purpose of c)amping

b&What factors go7ern the choice of a c)amping de7ices to achie7e the purpose of c)amping

discuss them in detai).


(G(


182/201

;a< )he purpose of clamping is to press the wor&piece against the locators and to maintain location in

opposition to all disturbing forces li&e cutting forces etc, which have tendency to upset the

fi%ation.

;b< 9our factors governing the choice of clamping devices are

;i< 9actors affecting the sizes of clamping forces needed for a particular application, where they

must and can be applied, and the direction in which these should acts are governed by ;i< type

of locator and position of the locating surfaces, ;ii< ruggedness or fratility of wor&piece.;iii


185/201

double cover but Hoint in which there is no possibility of bending of plate and very little possibilities of

bending of rivet.

T"pes of ri7eted Goints and nomerc)ature

According to a arrangement of rivets, the Hoints are called single riveted. 9igure ;a< ;b< and ;c


186/201


187/201

Digure< =o)ted Goint

+quare headed bo)t ,ith square nec9


188/201

)his bolt passes through a hole in one part only, while the other part is gripped by the hoo& shaped

bolt head. #t is used where there is no space for ma&ing a bolt hole in one of the parts. )he s+uare nec&

prevents the rotation of the bolt.;9igure

aircraft production tech

Documents