Beginning Metal Repair

Introduction• Herb Spenner

hspenner@gavilan.edu

• Background Electrical Engineer – Purdue, A&P – Gavilan College Gavilan Aviation Technology Instructor

• FAA Airframe and Power (A&P) mechanics program• A&P with IA (Inspection Authorization)• Teach General & Airframe classes

• Web based information http://hhh.gavilan.edu/hspenner/BeginMetal/

Class’s Starting Idea

Topics• Rules & Safety• Basic metal properties• Cleaning• Cutting• Drilling & tapping holes• Fasteners• Welding• Finishing

Projects• Drilling and Tapping

Cutting bar stock Drilling Tapping Bolt extraction Thread repair (Heli-Coil®)

Projects• Sheet Metal Welding

Cutting Cleaning Tack Butt Rosette Flanging Finishing

Projects• Rolling Cart

Cutting Cleaning Fitting Welding Joint reinforcement Finishing

Rules and Safety• Safety First!

Get instruction on equipment Eye protection and gloves required for all power tools Welding only with a helmet, jacket and gloves

• Proper Attire No loose fitting cloths Natural fiber cloths

• Nylon and Polyester will burn Long pants - blue jeans Closed toed shoes No loose jewelry

Rules and Safety• Act Professional

Respect the facilities• Don’t touch anything in a cabinet without asking• Don’t touch any of the students tools• Return all Gavilan tools to their proper place

Respect your colleagues

• No eating or smoking allowed in classroom or lab Drinks are acceptable

• Cleanup after yourself

Ferrous Metals• Ferrous metal is one that contains iron• Pure iron is too soft for most uses

Add carbon to iron and you get steel

• SAE - Society of Automotive Engineers SAE four-digit numbering system for identifying steel

• Hard steel, such as drill bits and taps, break very easily

• Heat treated, hardened & coated metals are not welded

CRES• Corrosion Resistant steel• Stainless steel• 10+% of chromium • 200 thru 400 series• Usually not as strong as carbon steel• Usually non-magnetic• Difficult to weld

Aluminum Alloys• Soft, lighter and more expensive than steel• Aluminum alloy four-digit identification system:

First digit - Alloy type Second digit - Modification of alloy

• Many of the stronger alloys corrode and can’t be welded

• Work hardens and fails dramatically• Steel fasteners will cause aluminum to corrode

Paint aluminum or use “sacrificial” washer

Copper Alloys• Alloys

Beryllium Zinc – makes brass Tin – makes bronze Aluminum Manganese

• Corrosion resistant• Becomes brittle when work hardened• Can’t be welded

Braze or solder

Cleaning Metal• All corrosion must be removed before welding

or paint• Steel corrosion removal

Scotch-Brite Sand paper File Grinder Wire brush or wheel Phosphoric acid

• e.g. Naval jelly

Cleaning Metal• Aluminum corrosion removal

Scotch-Brite Very fine sand paper Stain steel wire brush – not used on steel Phosphoric acid wash

• Copper Scotch-Brite Sand paper File Grinder Wire brush or wheel

Cleaning Metal• Oil must be removed before welding or painting

Denatured alcohol Acetone – fingernail polish remover

• Water test – water will form a film on clean metal If the water film “breaks”, the surface is not clean

Welding Puddle

Welding• Welding – a process that joins metal by melting

or hammering the work pieces until they are united together. Base metal must be melted Process must protect molten metal from

atmosphere Material (filler) is added to joint Filler material must match base metal Process must control the amount of heat and the

rate that filler is added

Weld Joints

Bead

Welding• Gas welding – The use of oxygen and acetylene

(oxy-acetylene) to create a flame that melts the metal to be welded Burning process protects metal Uses filler rods Medium hard to learn Portable Dirty Easy to add heat treating and cutting options

Welding• Shielded Metal Arc Welding (SMAW) –– “stick”

Arc welding process that uses a consumable flux-coated electrode

Flux melts and coats molten metal• Forms a glass like cover – must be remove• Helps remove impurities

Easy to learn Simple equipment Crude results Can be used outside Video

Welding• Gas Tungsten Arc Welding (GTAW) – an arc

welding process that uses a non-consumable tungsten electrode to produce the heat for the weld. TIG – Tungsten Inert Gas Shielding gas usually is argon or helium Similar to Gas Welding, except uses a electric arc Very clean/very sensitive to dirt Can’t be used in windy conditions Very hard to learn

Welding

Puddle

Welding• Gas Metal Arc Welding (GMAW) – MIG - a

method of welding in which the filler metal wire supplies the electric current to maintain the arc, which is shielded from the surrounding air by an inert gas, usually argon or carbon dioxide (CO2) Filler is automatically fed from reel of wire Easy to learn - one handed application Fast Can’t be used in windy conditions Dirty and splatters Difficult to determine the quality of the weld

Welding

Video

Welding

Video 1 Video 2

Welding• Flux Core – Combination of “stick” and MIG

welding Uses a MIG welding machine Welding wire is hollow with flux inside No shielding gas Easy to learn Can be used outside Dirty

Welding• Spot welding – Uses electric current to fuse two

pieces of sheet metal together No filler material Clean Easy to use Extensively used in the automotive industry Video

Weld Joints

Weld Joints

Tack Weld

Tack Weld

Rosette Weld

Video

Drill BitsSizes available in fraction of an inch, metric and numbered

Soft metals – high speed and light pressure

Hard metals – low speed and higher pressure

Reduce speed a bit size increases

Use oil for cleaning chips and cooling

Tap and Die

Tap

Die

Tap and Die• Threads

UNF – fine UNC – course National Taper Pipe (NTP)

• Tapered to seal fluids Rolled and cut

• Rolled is stronger

• Use matching drill size• Use cutting oil and/or grease (catch shavings)• 1/2 turn forward and then backup• Straight and slow

Tap

Plain Washers• Provides a smooth bearing surface• Protects surface from galling & corrosion

Must be used when using a locking washers

• Should be used under every bolt head and nut• When using lock washer, the order should be:

Bolt Plain washer Mating surface Plain washer Lock washer Nut

Metal Cutting• Abrasive chop saw

Good for bar stock Rough finish Hard to get accurate No oil

• Angle grinder Cutting wheel – abrasive

• Wears quickly Grinding disk - shaping Sanding disk - shaping

• Belt sander - shaping

Metal Cutting• Saws with teeth use oil• Hack saw

More teeth per inch (TPI) the finer the cutter If careful, can be very accurate Invest in a ridge frame

• Saber saw• Scrolling saw• Band saw• Shears

Home Welder• Invest in a good helmet• MIG best option• Be care of “MIG” core flux welders• Be care full of combo welders – inexpensive

ones may have to many compromises e.g. starter circuits May need “optional” equipment

• Find one with infinite (smooth) adjustments• Is 110 volt enough? – ¼” max welding• Cart with good wheels

Longevity MIG 140