Introduction to welding processes r1 1

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Introduction to welding processes r1 1

  1. 1. Introduction to welding 1
  2. 2. Introduction to weldingOverview 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. 3. Introduction to weldingWeld 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. 4. Introduction to weldingWelding 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. 5. Introduction to weldingBasic 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. 6. Introduction to weldingFusion welding heat sourcesElectric resistance Chemical reaction Electric arc Power beamsSpot, seam and Oxyfuel gas MMAW Laserprojection welding welding GMAW Electron beam GTAW FCAW Electroslag Thermit welding SAW 6
  7. 7. Introduction to weldingSolid phase welding  Hot processes q Forge welding q Friction welding q Diffusion bonding  Cold processes q Ultrasonic welding q Explosive welding 7
  8. 8. Introduction to weldingSome 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. 9. Introduction to weldingThe electric arc  Electric discharge between 2 electrodes through ionised gas Peak - Cathode q 10 to 2000 amps at 10 totemperatures 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. 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/minLow 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. 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. 12. Introduction to weldingManual Metal Arc Welding MMAW, SMAW, Stick electrode welding Manual welding 12
  13. 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. 14. Introduction to weldingManual Metal Arc Welding 14
  15. 15. Introduction to weldingManual Metal Arc WeldingMinimum 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. 16. Introduction to weldingManual Metal Arc WeldingProcess 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. 17. Introduction to weldingManual Metal Arc WeldingCovered 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. 18. Introduction to weldingManual Metal Arc WeldingFunctions 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. 19. Introduction to weldingManual Metal Arc WeldingAWS A5.1 classification E XXXX - HTensile Strength Hydrogen levelin 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. 20. Introduction to weldingManual Metal Arc WeldingApplications  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. 21. Introduction to weldingManual Metal Arc WeldingLimitations  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. 22. Introduction to weldingSubmerged arc welding SAW, Sub-arc 22
  23. 23. Introduction to weldingSubmerged arc welding 23
  24. 24. Introduction to weldingSubmerged arc welding 24
  25. 25. Introduction to weldingSubmerged 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. 26. Introduction to weldingSubmerged arc welding - Equipment  Power source  Welding head and control box  Welding head travel  Flux recovery system (optional)  Positioners and Fixtures 26
  27. 27. Introduction to weldingSubmerged 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. 28. Introduction to weldingSubmerged 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. 29. Introduction to weldingSubmerged arc weldingProcess 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. 30. Introduction to weldingSubmerged arc welding – Tandem arc 30
  31. 31. Introduction to welding Gas shielded arc processTungsten Inert Gas welding (TIG)Gas tungsten arc welding (GTAW) 31
  32. 32. Introduction to weldingGas 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. 33. Introduction to weldingGas Tungsten arc welding 33
  34. 34. Introduction to weldingGas 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. 35. Introduction to weldingGas 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. 36. Introduction to weldingGas 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. 37. Introduction to weldingGas 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. 38. Introduction to weldingGas 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. 39. Introduction to weldingGas Tungsten Arc Welding - Automation 39
  40. 40. Introduction to weldingGas Tungsten Arc Welding – A TIG 40
  41. 41. Introduction to welding GMAW and FCAW Gas metal arc welding(MIG, MAG, CO2 welding) Flux cored arc welding 41
  42. 42. Introduction to weldingGas 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. 43. Introduction to weldingGas metal arc welding 43
  44. 44. Introduction to weldingGas 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. 45. Introduction to weldingGas metal arc welding 45
  46. 46. Introduction to weldingGas 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. 47. Introduction to weldingGas 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. 48. Introduction to weldingGas metal arc welding – Metal transfer Burn-back and unstable arc Spray Voltage Globular Short circuiting No arc (birds-nesting) Current 48
  49. 49. Introduction to weldingGas 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. 50. Introduction to weldingGas metal arc welding – Wire size 50
  51. 51. Introduction to weldingGas 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. 52. Introduction to weldingGas metal arc welding - Developments 52
  53. 53. Introduction to weldingGas metal arc welding - Developments 53
  54. 54. Introduction to weldingGas metal arc welding - Developments 54
  55. 55. Introduction to weldingGas metal arc welding - Developments 55
  56. 56. Introduction to weldingPlasma Cutting, Welding & Surfacing 56
  57. 57. Introduction to welding 57
  58. 58. Introduction to weldingOxy-Acetylene Welding Oxidising Flame Carburising Flame Neutral Flame 58
  59. 59. Introduction to weldingThermit welding 59
  60. 60. Introduction to weldingLaser 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. 61. Introduction to weldingLaser welding 61
  62. 62. Introduction to weldingElectron 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. 63. Introduction to weldingElectron Beam Welding 63
  64. 64. Introduction to weldingSize of weld beads in(a) electron-beam or laser-beam welding(b) conventional arc welding. 64
  65. 65. Introduction to weldingSolid-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. 66. Introduction to weldingResistance Welding 66
  67. 67. Introduction to weldingResistance spot welding Robots 67
  68. 68. Introduction to weldingFlash Butt Welding 68
  69. 69. Introduction to weldingFriction Welding 69
  70. 70. Introduction to weldingFriction Stir Welding 70
  71. 71. Introduction to weldingFriction Stir Welding 71
  72. 72. Introduction to weldingExplosive Welding 72
  73. 73. Introduction to welding 73
  74. 74. Introduction to welding 74
  75. 75. ANY QUESTIONS 75
  76. 76. Introduction to welding 76
  77. 77. Introduction to welding 77
  78. 78. Introduction to welding 78
  79. 79. Introduction to welding 79
  80. 80. Introduction to welding 80
  81. 81. Introduction to welding 81
  82. 82. Introduction to welding 82
  83. 83. Introduction to welding 83
  84. 84. Introduction to welding 84
  85. 85. Introduction to weldingImportance 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. 86. Introduction to weldingFusion 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. 87. Introduction to weldingWhy 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. 88. Introduction to weldingAllied 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. 89. Introduction to welding 89
  90. 90. Introduction to weldingArc length Vs Arc voltage 90
  91. 91. Introduction to weldingElectrical characteristic of Arc 91
  92. 92. Introduction to weldingWelding Power Source Characteristic 92
  93. 93. Introduction to weldingTypical 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. 94. Introduction to weldingElectrodes 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. 95. Introduction to welding 95
  96. 96. Introduction to welding 96
  97. 97. Introduction to welding 97
  98. 98. Introduction to welding 98
  99. 99. Introduction to weldingHigh 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. 100. Introduction to weldingVee 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. 101. Introduction to welding 101
  102. 102. Introduction to weldingGMAW and FCAW 102
  103. 103. Introduction to weldingGMAW & FCAW processes 103
  104. 104. Introduction to weldingGMAW & FCAW processes 104
  105. 105. Introduction to weldingGMAW & FCAW processes 105
  106. 106. Introduction to weldingGMAW & FCAW processes 106
  107. 107. Introduction to welding 107
  108. 108. Introduction to welding 108
  109. 109. Introduction to weldingArc-air Gouging 109
  110. 110. Introduction to welding 110
  111. 111. Introduction to welding 111
  112. 112. Introduction to welding 112
  113. 113. Introduction to weldingOxy-acetylene Cutting & Gouging 113
  114. 114. Introduction to welding 114

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