Introduction to welding processes r1 1
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Introduction to welding processes r1 1
- 2. Introduction to welding Overview of joining methods Mechanical methods q Screwed fasteners, rivets, Adhesive bonding Brazing and Soldering q Base metal does not fuse. q Molten filler drawn into close-fit joints by capillary action (surface tension forces). q Brazing filler melts >450 C, solder <450 C Welding 2
- 3. Introduction to welding Weld A joint produced by heat or pressure or both So there is continuity of material. Filler (if used) has a melting temperature close to the base material 3
- 4. Introduction to welding Welding processes Fusion welding q Welding in the liquid state with no pressure q Union is by molten metal bridging Solid phase welding q Carried out below the melting point without filler additions q Pressure often used q Union is often by plastic flow 4
- 5. Introduction to welding Basic Requirements of Welding Process Source of Heat Chemical Reaction Electrical - Arc, Resistance, Induction Mechanical Protection from Atmosphere Gas Shielding Flux Mechanical Expulsion Vacuum 5
- 6. Introduction to welding Fusion welding heat sources Electric resistance Chemical reaction Electric arc Power beams Spot, seam and Oxyfuel gas MMAW Laser projection welding welding GMAW Electron beam GTAW FCAW Electroslag Thermit welding SAW 6
- 7. Introduction to welding Solid phase welding Hot processes q Forge welding q Friction welding q Diffusion bonding Cold processes q Ultrasonic welding q Explosive welding 7
- 8. Introduction to welding Some arc welding processes MMAW - manual metal arc welding SAW - submerged arc welding GTAW - gas tungsten arc welding (TIG) GMAW - gas-metal arc welding (MIG, MAG) FCAW - flux cored arc welding 8
- 9. Introduction to welding The electric arc Electric discharge between 2 electrodes through ionised gas Peak - Cathode q 10 to 2000 amps at 10 to temperatures drop zone 500 V arc voltage 18,000 K Column of ionised gas at high temperature Forces stiffen the arc column q Transfer of molten metal Anode from electrode to workpiece drop zone Can have a cleaning action, + breaking up oxides on workpiece 9
- 10. Introduction to welding Arc energy Q = arc energy in kJ/mm Q E x E = current in amps = I V I = arc voltage V = travel speed in mm/min Low arc energy High arc energy • Small weld pool size • Large weld pool size • Incomplete fusion • Low cooling rate • High cooling rate • Increased solidification cracking risk • Unwanted phase transformations • Low ductility and strength • Hydrogen cracking • Precipitation of unwanted phases (corrosion and ductility) 10
- 11. Introduction to welding • 103 Watts/cm2 melts most metals • 106 -107 Watts/cm2 vaporizes most metals • 103 to 106 Watts/cm2 typical for fusion welding 11
- 12. Introduction to welding Manual Metal Arc Welding MMAW, SMAW, Stick electrode welding Manual welding 12
- 13. Introduction to welding Manual Metal Arc Welding Heat source - arc between metal and a flux coated electrode (1.6- 8 mm diameter) • Current 30-400A (depends on electrode size) • AC or DC operation • Power 1 to 12 kW 13
- 14. Introduction to welding Manual Metal Arc Welding 14
- 15. Introduction to welding Manual Metal Arc Welding Minimum equipment Power source (ac or dc, engine driven or mains transformer) Electrode holder and leads q May carry up to 300 amps Head shield with lens protects face & eyes Chipping hammer to remove slag Welding gloves protect hands from arc radiation, hot material and electric shock 15
- 16. Introduction to welding Manual Metal Arc Welding Process features Simple portable equipment Widely practiced skills Applicable to wide range of materials, joints, positions About 1kg weld deposited per arc-hour Portable and versatile Properties can be excellent Benchmark process 16
- 17. Introduction to welding Manual Metal Arc Welding Covered electrodes Core wire q Solid or tubular q 2mm to 8mm diameter, 250 to 450mm long Coating q Extruded as paste, dried to strengthen q Dipped into slurry and dried (rare) q Wound with paper or chord (obsolete) 17
- 18. Introduction to welding Manual Metal Arc Welding Functions of coating Slag protects weld pool from oxidation Gas shielding also protects weld pool Surface tension (fluxing) Arc stabilising (ionising) Alloying and deoxidation Some ingredients aid manufacture (binder and extrusion aids) 18
- 19. Introduction to welding Manual Metal Arc Welding AWS A5.1 classification E XXXX - H Tensile Strength Hydrogen level in KPSI (H mR) H = 5 ml / 100g of WM R = low moisture pick- up Useable positions Flux type 1=all positions 20 = Acidic (iron oxide) 2=flat + horizontal 10, 11 = Cellulosic 4=vertical down 12, 13 = Rutile 24 = Rutile + iron powder 27 = Acidic + iron powder 16 = basic 18, 28 = basic + iron powder
- 20. Introduction to welding Manual Metal Arc Welding Applications Wide range of welded products: q light structure & Heavy steel structures q Workshop and site q High integrity (nuclear reactors, pressure equipment) Ideal where access is difficult - construction site, inside vessels, underwater Joins a wide range of materials 20
- 21. Introduction to welding Manual Metal Arc Welding Limitations Low productivity q Low power q Low duty cycle (frequent electrode changes) Hydrogen from flux coatings Electrode live all the time q Arc strike, stray current and electric shock risks 21
- 22. Introduction to welding Submerged arc welding SAW, Sub-arc 22
- 23. Introduction to welding Submerged arc welding 23
- 24. Introduction to welding Submerged arc welding 24
- 25. Introduction to welding Submerged arc welding - Features High productivity q 2 to 10 kg/hour q Up to 2m/min Bulky, expensive and heavy equipment Flat and horizontal positions only Thicker sections (3mm and above) Mostly ferrous materials (also Ni alloys)
- 26. Introduction to welding Submerged arc welding - Equipment Power source Welding head and control box Welding head travel Flux recovery system (optional) Positioners and Fixtures 26
- 27. Introduction to welding Submerged arc welding - Consumables Solid or cored wires Granular fluxes q Agglomerated, fused or sintered q Alloying activity • Contribution to weld metal chemistry from flux q Basicity • Acid fluxes made from manganese oxide, silica, rutile are easy to use • Basic fluxes (MgO, CaO, CaF2, Al2O3) provide excellent toughness welds 27
- 28. Introduction to welding Submerged arc welding - Applications Long straight welds in heavier material q Vessel longitudinal and circumferential welds q Flange to web joints of I beams Flat or horizontal position q Flux has to be supported Access has to be good 28
- 29. Introduction to welding Submerged arc welding Process variations Surfacing and hardfacing q Wire and strip electrodes Semi-automatic Multiple electrodes q 2 (and more) electrode wires q From one or more power sources Iron powder additions to groove 29
- 30. Introduction to welding Submerged arc welding – Tandem arc 30
- 31. Introduction to welding Gas shielded arc process Tungsten Inert Gas welding (TIG) Gas tungsten arc welding (GTAW) 31
- 32. Introduction to welding Gas Tungsten Arc Welding Alternative names - GTAW,TIG (Tungsten Inert Gas), Argonarc Heat source is an electric arc between a non- consumable electrode and the workpiece Filler metal is not added or is added independently 32
- 33. Introduction to welding Gas Tungsten arc welding 33
- 34. Introduction to welding Gas Tungsten Arc Welding Heat source - arc between a tungsten tip and the parent metal •30-400A, AC or DC •10-20V •0.3-8kW Inert gas shielding Consumable filler rod can be used (1 to 4mm diameter) 34
- 35. Introduction to welding Gas Tungsten Arc Welding - Process features Excellent control q Stable arc at low power (80A at 11V) q Independently added filler q Ideal for intricate welds eg root runs in pipe or thin sheet q Low productivity 0.5kg/h manual High quality q Clean process, no slag q Low oxygen and nitrogen weld metal q Defect free, excellent profile even for single sided welds 35
- 36. Introduction to welding Gas Tungsten Arc Welding - Equipment Welding power source with constant current characteristic q DC for most metals, AC for Al q Arc starting by high frequency (5000V, 0.05A) q Sequence timers for arc starting, arc finishing & gas control Water- or gas-cooled torch with tungsten electrode q Electrode may contain thoria or zirconia, etc
- 37. Introduction to welding Gas Tungsten Arc Welding - Shielding gases Torch is fed with an inert or reducing gas q Pure argon - widespread applications q Argon-helium - Higher arc voltage, inert q Argon-2% hydrogen - Cu alloys & austenitic steel q Torch gas must not contain oxygen or CO2 Backing (or purge) gas q Used for all single-sided welds except in carbon steel q Argon, nitrogen, formier gas (N2 + H2) Supplementary shielding q Reactive metals: Ti, etc q Gas filled chambers or additional gas supply devices 37
- 38. Introduction to welding Gas Tungsten Arc Welding - Filler metals Autogenous welding (no filler) Filler wire or rod of matching composition q C-Mn & low alloy steel q Stainless Steel q Al, Mg, Ti q Cu & Ni Consumable inserts - filler preplaced in joint 38
- 39. Introduction to welding Gas Tungsten Arc Welding - Automation 39
- 40. Introduction to welding Gas Tungsten Arc Welding – A TIG 40
- 41. Introduction to welding GMAW and FCAW Gas metal arc welding (MIG, MAG, CO2 welding) Flux cored arc welding 41
- 42. Introduction to welding Gas metal arc welding A continuous solid wire, small diameter q GMAW uses solid wire, no flux q FCAW uses flux-filled wire Fed through the gun to the arc by wire feeder. The weld pool may be protected from oxidation by shielding gas. High productivity 3 kg/h or more Direct current (DCEP mostly) 42
- 43. Introduction to welding Gas metal arc welding 43
- 44. Introduction to welding Gas metal arc welding MIG Welding Heat source - arc between parent metal and consumable electrode wire (0.6 to 1.6mm diameter) •60-500A, DC only •16-40V •1 to 20kW 44
- 45. Introduction to welding Gas metal arc welding 45
- 46. Introduction to welding Gas metal arc welding - Equipment Welding power source Wire feeder mechanism q May be in power source cabinet Gun with gas supply & trigger switch q Manual (semiautomatic) guns q Automatic torches available q Can be fitted to robot etc 46
- 47. Introduction to welding Gas metal arc welding – Metal transfer Spray q Higher current & voltage, argon-rich gas Short circuiting (dip) q Low current and voltage, CO2 Globular q Intermediate current Pulsed current power sources q Adjustable frequency q One droplet per current pulse.
- 48. Introduction to welding Gas metal arc welding – Metal transfer Burn-back and unstable arc Spray Voltage Globular Short circuiting No arc (birds-nesting) Current 48
- 49. Introduction to welding Gas metal arc welding - Consumables Solid Wires (GMAW) q A wide variety of alloys are available Flux cored arc welding (FCAW) q Gas shielded flux cored wires q Self-shielded flux cored wires • Used outdoors q Metal cored wires • Light flux cover 49
- 50. Introduction to welding Gas metal arc welding – Wire size 50
- 51. Introduction to welding Gas metal arc welding - Gas mixtures Inert gases (MIG) q Argon or helium or mixtures of these q Active base metals, Al, Mg, Ti Active gases (MAG and FCAW) q Carbon dioxide q Argon plus oxygen and/or carbon dioxide q Nitrogen, hydrogen 51
- 52. Introduction to welding Gas metal arc welding - Developments 52
- 53. Introduction to welding Gas metal arc welding - Developments 53
- 54. Introduction to welding Gas metal arc welding - Developments 54
- 55. Introduction to welding Gas metal arc welding - Developments 55
- 56. Introduction to welding Plasma Cutting, Welding & Surfacing 56
- 57. Introduction to welding 57
- 58. Introduction to welding Oxy-Acetylene Welding Oxidising Flame Carburising Flame Neutral Flame 58
- 59. Introduction to welding Thermit welding 59
- 60. Introduction to welding Laser Welding • Photons transmit energy and heat • Energy intensity up to 109 Watts/cm2 • Depth to width of hole up to 50x • Automatic controllers needed • 90% efficiency • Reflectors don’t weld easily 60
- 61. Introduction to welding Laser welding 61
- 62. Introduction to welding Electron Beam Welding • Electrons strike surface and generate heat • Best performed in a vacuum • Workpiece must be a conductor • Magnetic fields affect beam • Current to 1/2 A • Power to 100 kW • X-rays produced 62
- 63. Introduction to welding Electron Beam Welding 63
- 64. Introduction to welding Size of weld beads in (a) electron-beam or laser-beam welding (b) conventional arc welding. 64
- 65. Introduction to welding Solid-State Welding q Heat q Pressure q Time q NO Melting q NO Filler Material q Intimate Contact Usually Requires Deformation q Works with Dissimilar Metals 65
- 66. Introduction to welding Resistance Welding 66
- 67. Introduction to welding Resistance spot welding Robots 67
- 68. Introduction to welding Flash Butt Welding 68
- 69. Introduction to welding Friction Welding 69
- 70. Introduction to welding Friction Stir Welding 70
- 71. Introduction to welding Friction Stir Welding 71
- 72. Introduction to welding Explosive Welding 72
- 73. Introduction to welding 73
- 74. Introduction to welding 74
- 75. ANY QUESTIONS 75
- 76. Introduction to welding 76
- 77. Introduction to welding 77
- 78. Introduction to welding 78
- 79. Introduction to welding 79
- 80. Introduction to welding 80
- 81. Introduction to welding 81
- 82. Introduction to welding 82
- 83. Introduction to welding 83
- 84. Introduction to welding 84
- 85. Introduction to welding Importance of Welding Wide use in manufacture Occurs later stage in manufacturing process q Large number of practitioners q Cost is high proportion of manufactured item q Risk and cost of defective welds is high Technology is complex q Process control is key to success 85
- 86. Introduction to welding Fusion welding Intense energy source melts base metal locally q Energy density 0.001 W/cm2 to 1 MW/cm2 q Energy source may be stationary or move at a constant speed Filler metal q From electrode q Independently added filler q No filler (autogenous welding) 86
- 87. Introduction to welding Why metals do not weld Surface irregularities Surface contamination q Adsorption - A one atom boundary layer forms in 10-9 sec at 100 kPa and in 10-3 sec at a pressure of 1Pa q Chemical combination (oxidation) Joining can occur where heat or pressure are present ( ex: seizing) 87
- 88. Introduction to welding Allied processes Thermal cutting q Oxyfuel gas, plasma, laser cutting Gouging q Air-arc, plasma, oxyfuel gas Surfacing q Powder and arc spray coating q Clad welding, hardfacing 88
- 89. Introduction to welding 89
- 90. Introduction to welding Arc length Vs Arc voltage 90
- 91. Introduction to welding Electrical characteristic of Arc 91
- 92. Introduction to welding Welding Power Source Characteristic 92
- 93. Introduction to welding Typical coating constituents Organic materials (Cellulose) Titanium dioxide (rutile) Silica, alumino-silicates Sodium and potassium silicate binders Calcium carbonate and fluoride Iron powder, ferro-alloys 93
- 94. Introduction to welding Electrodes for C-Mn Steel E6010, E6011 - cellulosic q Punchy, penetrating arc E6012, E6013 - rutile q Smooth arc, general purpose E7024 - iron powder (rutile) q Thick coating, high deposition E7016, E7018, E7028 - Basic low hydrogen q High toughness, low cracking risk 94
- 95. Introduction to welding 95
- 96. Introduction to welding 96
- 97. Introduction to welding 97
- 98. Introduction to welding 98
- 99. Introduction to welding High dilution procedures Square edges Low cost of preparation Fast travel speeds (acid Single pass with temporary backing fluxes) Maximum thickness q 16 mm in one pass, 20 mm in two Location of bead is critical High dilution leads to low toughness High cap height, lower Two pass weld fatigue life
- 100. Introduction to welding Vee butt weld procedures 60 One, two or multipass included Vee or U preparations Lower currents Unlimited thickness Excellent quality 6mm 1.5mm max 100
- 101. Introduction to welding 101
- 102. Introduction to welding GMAW and FCAW 102
- 103. Introduction to welding GMAW & FCAW processes 103
- 104. Introduction to welding GMAW & FCAW processes 104
- 105. Introduction to welding GMAW & FCAW processes 105
- 106. Introduction to welding GMAW & FCAW processes 106
- 107. Introduction to welding 107
- 108. Introduction to welding 108
- 109. Introduction to welding Arc-air Gouging 109
- 110. Introduction to welding 110
- 111. Introduction to welding 111
- 112. Introduction to welding 112
- 113. Introduction to welding Oxy-acetylene Cutting & Gouging 113
- 114. Introduction to welding 114