AMT 110 Welding Chapter 5 Welding •  Welding – a process that joins metal by mel=ng or hammering the work pieces un=l they are united together. •  Gas welding – The use of oxygen and acetylene (oxy-­‐acetylene) to create a flame that melts the metal to be welded •  Shielded Metal Arc Welding (SMAW) –– “s=ck” Arc welding process that uses a consumable flux-­‐
coated electrode   Flux melts and coats molten metal   Not used in avia=on   Video 
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) Used in robo=c welding   Good for adding a lot of filler   One handed applica=on   Difficult to determine the quality of the weld 
Welding Video
Welding Video 1
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Welding •  Gas Tungsten Arc Welding (GTAW) – an arc welding process that uses a non-­‐consumable tungsten electrode to produce the heat for the weld. The weld area is protected from atmospheric contamina=on by a inert shielding gas, and a filler metal is normally used 
TIG – Tungsten Inert Gas •  Heliarc or Heliweld Similar to Gas Welding, except uses a electric arc   Very clean   Shielding gas usually is argon or helium 
Welding Welding Puddle
Video
Welding Video
Welding •  Spot Weld – Video Used in mass manufacturing -­‐ video   Used only on sheet metal   Hand units available – video 
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Seam welding – video Fric=on welding – video Fric=on s=r welding -­‐ video Plasma cu[ng – video Oxy-­‐acetylene cu[ng – video 
Extra oxygen is added to burn through the metal Welding Gas •  Acetylene – video 1 video 2 Fuel for oxy-­‐acetylene welding and cu[ng   Chemically unstable   Storage cylinders contain porous material (like charcoal) and acetone 
•  Helps put acetylene in solu=on Pure acetylene is explosive at 29.4 psi   Never use pressures above 15 psi 
•  Working pressure is about 5 to 7 psi 
Full tank is maximum of 250 psi •  Don’t empty below 50 psi •  Acetylene Welding Gas Tank must be kept standing to ensure acetone stays in boale   Tank has female fi[ng, leb hand thread 
•  Regulator has notches on the hex fi[ng to indicate leb hand thread Hose is red   Sold by weight used 
•  Oxygen Welding Gas Using to increase the combus=on rate of acetylene   Different than avia=on oxygen for aircrab   Green hose & tank   The oxygen can cause an item to spontaneously combust 
•  Do not use lubricants on fits, a fire may result 
Full tank is about 3,000 psi •  Working pressure is about 15 to 20 psi 
Tank has male fi[ng, right hand thread •  Argon 
Welding Gas Inert shielding gas for TIG & MIG •  Helium 
Inert shielding gas for TIG •  CO2 
Chemically stable shielding gas for MIG •  Hydrogen 
Used for fuel in gas welding Pressure Regulators •  Reduces high pressure in tanks 
Reduce pressure •  Gas welding 
Reduce pressure and establish flow rate •  Shielding gas •  Single or Two stage 
Two stage is more accurate and larger in size Single Stage Pressure Regulators Two Stage Pressure Regulators Gas Welding Tools •  Tanks are seamless steel •  Duplex hose (double hose) Red is acetylene with leb hand threads   Green is oxygen with right hand threads 
•  Check valve and Flashback arrestor Stops reverse flow of gas   Between regulator and hose or hose and torch 
•  Welding torch Equal pressure torch   Acetylene and oxygen valves 
•  Torch =ps Gas Welding Tools Used to control the amount of torch heat generated   Comes in numbered sizes 
•  Size of =p opening 
Oben clogs with carbon deposits •  Must use =p cleaner 
Rosebud =p looks like a shower head and is used to heat bigger areas •  Protec=ve apparel Goggles to shade flame (different than arc helmet)   Leathers – jacket, apron, gloves 
Gas Welding Tools •  Torch lighter 
Spark type •  Cu[ng Torch 
Used to add/control a jet of extra oxygen to cut through metal •  Flame Gas Welding Turn acetylene on first, light and adjust amount of gas   Turn on oxygen and adjust oxygen to get correct burn ra=o 
•  Flashback/backfire Flame moving back up the hose   Caused by =p touching work, overheated =p, wrong opera=ng pressure, loose +p, or dirty =p   Shut gasses off and fix cause 
Gas Welding Video
Gas Welding •  Flame 
Gas Welding Neutral Flame •  Perfect gas mixture balance •  Most work is done with this type of flame 
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FAA recommends for aluminum Carburizing Flame •  Too much acetylene •  Adds carbon to mild steel and cause it to get too hard and briale •  Use slightly carburizing flame for stainless steel (CRES) 
Too much carbon added and the stainless steel will lose its resistance to corrosion •  Flame 
Gas Welding Oxidizing Flame •  Has a hissing sound •  Too much oxygen 
Sob/Hard Flame •  Independent of mixture ra=o •  More or less amount of gas mixture 
Doesn’t effect the amount of heat, the =p size determines the amount of heat •  Usually use a sob flame 
Especially for aluminum •  Shutdown Gas Welding Close acetylene on torch   Close oxygen on torch   Close both tanks   Vent both hoses and then close hose valves   “Back off” regulator valves 
Welding Notes •  Use the filler rod that matches the material 
Usually the same base metal •  Gas welding aluminum usually requires flux Apply to the welding surface and the filler rod   Removes the oxides that have formed and covers the weld so new oxides cannot form during the weld 
•  Most heat treated metal can not be welded 
The metal will lose its strength from heat trea=ng •  Grinding a welded joint will reduce its strength •  Don’t re-­‐weld a porous joint 
Grind old weld off before re-­‐welding Welding Notes •  Clean joint and rod before welding •  Tack weld pieces in place before fully welding •  Thick aluminum may need to be preheated before welding to reduce stress and get complete penetra=on •  Welded structures may need to be annealed aber welding to release stresses caused by welding heat 
Annealing is the process of hea=ng a metal to the point where stress is relieved •  Annealing will soben the metal a liale Brazing and Soldering •  Brazing and Soldering are very similar 
Brazing usually implies a higher temperature and the use of a copper based filler (bronze and brass) •  The filler material is non-­‐ferrous (not iron or steel) •  The pieces being joint are never melted •  Brazing is done with a flame •  Soldering is done with a flame or an “iron” Brazing and Soldering •  Flux is used to clean and remove oxides from surfaces Can help in preven=ng oxides from forming during brazing or soldering   Can help with the “flow” of filler 
•  Welding is the strongest joint, next brazing and then soldering •  Brazing and soldering can contaminate the surface of the jointed pieces 
The surfaces of the pieces must be ground clean before welding Brazing and Soldering •  Brazing can be used to joint two dissimilar metals •  Soldering is used in electronics and plumbing 
Capillary ac=on is used to “wick up” solder into a joint •  Electrical components should be mechanically cleaned before soldering •  Soldering iron surface must be “=nned” before using 
Fresh coat of solder applied to the iron’s surface •  A thin, pointed =p on a soldering copper (iron) is normally undesirable because it cools too rapidly Bead Bead Bead Bead Too rapid
Too hot
Oxidized flame
Too cold
Rough edges
Too much
acetylene
Inconsistent
Too cold
Weld Joints Weld Joints Weld Joints Weld Joints Fishmouth Joint Video 1
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Roseae Weld Video
Patch Plate Welded Sleeve Edge Notch