AMT 110 Welding. Chapter 5

Transcription

1 AMT 110 Welding Chapter 5

2 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 fluxcoated electrode! Flux melts and coats molten metal! Not used in avia=on! Video

3 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 (CO 2 )! Used in robo=c welding! Good for adding a lot of filler! One handed applica=on! Difficult to determine the quality of the weld MIG etch test

4 Welding Video

5 Welding Video 1 Video 2

6 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

7 Welding

8 Welding Puddle Video

9 Welding Video

10 Welding Spot Weld Video! Used in mass manufacturing - video! Used only on sheet metal! Hand units available video 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

11 Plasma Cu[ng Plasma: high energy state of a gas; molecules are ionized, meaning they can conduct electrons! Fire and lightening are everyday examples of plasma Arc: the plasma of an electric discharge; surrounding gas is only par=ally ionized Plasma arc: gas is forced through arc, so more gas is ionized Plasma torch supplies electrical energy to a high velocity gas and changes it into plasma Nozzle =p focuses plasma; arc is very localized and has intense heat

12 Plasma Cu[ng Unlike oxy fuel cu[ng, oxida=on is not required; the focused, intense heat and high velocity melts the metal and severs it from the work piece Compressed air is the most commonly used gas

13 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 20 psi

14 Acetylene Welding Gas! Tank must be kept standing to ensure acetone stays in bodle! Tank has female fi[ng, lee hand thread Regulator has notches on the hex fi[ng to indicate lee hand thread! Hose is red! Sold by weight used

15 Oxygen Welding Gas! Using to increase the combus=on rate of acetylene! Different than avia=on oxygen for aircrae! Green hose & tank! The oxygen can cause an item to spontaneously combust Do not use lubricants on fi[ngs, a fire may result! Standard tank is 2200psi when full Working pressure is about 5 psi! Tank has male fi[ng, right hand thread

16 Argon Welding Gas! Inert shielding gas for TIG & MIG! Heavier than air (good for flat welding)! Ionizes easily in TIG (good arc star=ng, AC opera=on)! Provides cleaning ac=on in DCEP, AC opera=on! Affordable Helium! Inert shielding gas for TIG! Lighter than air (needs high flow rates)! Strong arc force (deep penetra=on)! Does not provide cleaning ac=on! Difficult to ionize

17 CO 2 Welding Gas! Chemically stable shielding gas for MIG! Added to argon for short-circuit MIG for stronger arc force! Typically 25% CO 2, 75% Argon Hydrogen! Mainly used for fuel in gas welding! Combus=on by-product is H 2 O (very clean flame)! Low temperature flame (good for aluminum)! Reducing flame produces no carbon (good for aluminum)! Expensive and requires regular leak tes=ng

18 Pressure Regulators Reduces high pressure in tanks! Reduce pressure Gas welding (working pressure calibrated in psi)! Reduce pressure and establish flow rate Shielding gas (working pressure in CFM) 1 2 3

19 Pressure Regulators Single or Two stage! Single stage will raise the working pressure as the inlet pressure decreases! Dual stage is larger and can keep working pressure constant as bodle pressure decreases

20 Single Stage Pressure Regulators

21 Two Stage Pressure Regulators

22 Gas Welding Tools Tanks are seamless steel Duplex hose (double hose)! Red is acetylene with lee hand threads! Green is oxygen with right hand threads Check valve and Flashback arrestor! Check valve stops reverse flow of gas! Flashback arrestor allows gases to pass through sintered cylinder, but prevents flame from passing! Between regulator and hose or hose and torch

23 Gas Welding Tools Welding torch! Equal pressure torch! Acetylene and oxygen valves Torch =ps! Used to control the amount of torch heat generated! Comes in numbered sizes Size of =p opening! Oeen clogs with carbon deposits Must use =p cleaner! Rosebud =p looks like a shower head and is used to heat bigger areas

24 Gas Welding Tools Torch lighter! Spark type Cu[ng Torch! Used to add/control a jet of extra oxygen to cut through metal Protec=ve apparel! Goggles to shade flame (different than arc helmet)! Leathers jacket, apron, gloves

25 Flame Gas Welding! Turn acetylene on first, light with striker, and adjust amount of gas un=l the smoke dies down! Turn on oxygen and adjust oxygen un=l a neutral flame is formed! A carburizing or oxidizing flame is best adjusted star=ng from a neutral flame! Primary combus=on inner cone Acetylene and oxygen form into carbon monoxide and hydrogen! Secondary combus=on outer envelope Carbon monoxide and oxygen form carbon dioxide (CO 2 shields the puddle) Hydrogen and oxygen form water vapor

26 Video Gas Welding

27 Gas Welding

28 Flame! Oxidizing Flame Gas Welding Has a hissing sound Too much oxygen, will cause porosity in the weld Porosity can be minimized by slowly cooling the weld Used for welding bronze and copper, and for brazing! Soe/Harsh Flame Independent of mixture ra=o Indicates velocity of gas mixture! Neutral soe flame is quiet! Neutral harsh flame has a rushing sound Soe flame is used for aluminum to avoid blowing holes in metal

29 Flame! Neutral Flame Gas Welding Perfect gas mixture balance Will not contaminate a weld Most work is done with this type of flame! FAA recommends for aluminum! Carburizing Flame Too much acetylene Adds carbon to mild steel and cause it to get too hard and bridle Use slightly carburizing flame for stainless steel (CRES)! CRES oxidizes easily! Too much carbon added and the stainless steel will lose its resistance to corrosion! Acetylene feather should be about 1/16

30 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

31 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 to avoid inclusions from contaminants

32 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 aeer 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 soeen the metal a lidle

33 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)! Brazing rod melts around 1700 F! Soe solder melts at 360 F! For comparison, steel melts around 2700 F The filler material is non-ferrous (not iron or steel) Base metal is never melted, just heated. Brazing is done with a flame or arc Soldering is done with a flame or an iron

34 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 joined pieces! The surfaces of the pieces must be ground clean before welding

35 Brazing and Soldering Brazing can be used to join 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 irons surface A thin, pointed =p on a soldering copper (iron) is normally undesirable because it cools too rapidly

36 Bead

37 Bead

38 Bead Good penetration Reinforcement has nice transition to base metal Consistent width

39 Bead Too rapid Too hot Oxidized flame Too cold Rough edges Too much acetylene Inconsistent Too cold

40 Weld Joints

41 Weld Joints

42 Weld Joints

43 Weld Joints Thick joints requiring multiple passes How small bevel is depends on if you can get torch in for root pass

44 Fishmouth Joint Video 1 Video 2 Video 3 Video 4

45 Rosede Weld Rosette welds are typically ¼ of the tube diameter, but not always Welded along perimeter Video

46 Patch Plate Fingers on patch plate extend 1½ times the tube diameter Plate thickness is the same as longeron thickness Tack weld plate to longeron; then heat plate and form it around cluster Weld entire perimeter of patch plate

47 Welded Sleeve

48 Edge Notch