Welding for engineers chapter 1

11,655 views

Published on

Welding for engineers chapter 1

  1. 1. Welding Technology for Engineers Welding for Engineers 1
  2. 2. Content:Chapter 1: Welding Processes and EquipmentChapter 2: Materials and their Behaviours in WeldingChapter 3: Design and ConstructionChapter 4: Fabrication and Application Engineering Welding for Engineers 2
  3. 3. Chapter 1:Welding Processes and Equipment Welding for Engineers 3
  4. 4. Welding Introduction Welding for Engineers 4
  5. 5. Requirements for Joining Materials Welding for Engineers 5
  6. 6. Surface Roughness Welding for Engineers 6
  7. 7. To make up atomic interaction of materials(1) Deform them – Pressure Welding – Solid State Bonding, Hot Pressing , …etc(2) Introduce molten metal between them – Brazing, Soldering, ..etc – Hot Pressing with metal insert, ..etc(3) Melt them – Fusion Welding – Arc Welding, Resistance Welding , …etc Welding for Engineers 7
  8. 8. Typical Weld Joints(a) Fusion Welding (b) Pressure Welding (c) Brazing Welding for Engineers 8
  9. 9. Fusion Welding – A welding process where metalworkpieces are joined through melting (fusing) andsolidifying. Molten metal id formed by heating, and is madeup from base metal, or from mixture of base metal and fillermetal.Pressure Welding – A welding process that forms a weldjoint by pressure of mechanical force after heating up thejoint by friction or other heat effects.Brazing and Soldering – joining processes that form a jointby filling gap with molten brazing filler metal after heatingthe joint. Capillary force induces the filling. Brazing fillermetal has a lower melting point than that of the base metalso that the base metal does not melt. Welding for Engineers 9
  10. 10. Brazing and SolderingClassification of Metal Joining Methods Welding for Engineers 10
  11. 11. Classification of Joining Methods of Metals Welding for Engineers 11
  12. 12. Fusion WeldingAdvantages:(1) Joint efficiency is high(2) Air and water tightness is excellent(3) Structure of joint can be simplified(4) Thickness of joint ranges is wide(5) Reduction of material usage and saving of workforceLimitations:(1) Newly formed weld joint is heterogeneous to the base metal(2) Quality of the base metal locally deteriorates by the welding heat(3) Weld strain and deformation occur by local heating and cooling(4) Residual stress develops and deteriorates the joint strength(5) It is difficult to confirm quality of the weld joint Welding for Engineers 12
  13. 13. Classification of Gas Shielded Arc Welding Welding for Engineers 13
  14. 14. Overview of Common Welding Methods Welding for Engineers 14
  15. 15. Welding PositionsSketch of a Weld Joint Welding Positions Welding for Engineers 15
  16. 16. Power Sources for WeldingAC Arc Welding Power Source• Shielded (Manual ) Metal Arc Welding• Electro-Slag Welding• TIG for Aluminum Alloys (cleaning action)• Submerged Arc WeldingDC Arc Welding Power Source• MIG/MAG Welding• Electro-Gas Arc Welding• CO2 Gas Arc Welding with Flux Cored Wire• Self Shielded Arc Welding• TIG for Steel• Plasma Welding and Cutting• Stud Welding• Submerged Arc Welding with small diameter wire Welding for Engineers 16
  17. 17. Characteristics of Arc Welding for Engineers 17
  18. 18. Characteristic of Arc• Voltage-Current relationship• Voltage distribution (a) Distribution of Arc Voltage (b) Arc Characteristics Welding for Engineers 18
  19. 19. Heat (Energy) Sources• Electric energy Arc Welding, Electro-Slag Welding, Resistance Welding, Electron Beam Welding, etc…• Mechanical energy Friction Welding, Friction Stir Welding, Ultrasonic Welding, etc…• Chemical energy Gas Welding, Thermit Welding, etc…• Photon energy Laser Welding, etc… Welding for Engineers 19
  20. 20. Temperature Profile of TIG Arc Welding for Engineers 20
  21. 21. Structure of Arc• Arc Voltage is a sum of cathode drop voltage, arc column voltageand anode drop voltage.• Arc Column Voltage increases as Arc Length increases. Welding for Engineers 21
  22. 22. Relationship between Welding Current and Arc Voltage Welding for Engineers 22
  23. 23. Electromagnetic Pinch EffectElectromagnetic attractive force causes the cross section of thearc to shrink – Electromagnetic Pinch Effect.Arc also shrinks to reduce its surface area to suppress heat losswhen the arc is cooled from ambient – Thermal Pinch Effect Welding for Engineers 23
  24. 24. Plasma Gas Flow• Magnetic field is made up around the arc by welding current.• The induced flow of gas directs from the electrode towards the workpiece, and its speed is high. This induced gas flow is Plasma Gas Flow.• The plasma gas flow strongly influences the transfer of molten metal droplets and penetration shape of weld. Welding for Engineers 24
  25. 25. Arc Blow(a) Effect of Work Piece Lead Connection (b) Effect of Work Piece Shape• Arc deflects from its intended direction by asymmetric magnetic field and welding current circuit (residual magnetic field) – Arc Blow.• Arc Blow tends to occur at DC welding of easily magnetized material, e.g. ferritic steel.• Elimination: Managing workpiece connection, leads (cables) & demagatizing workpieces. Welding for Engineers 25
  26. 26. Waveform Traces of Welding Voltage and Current of AC Arc P = Reignition Voltage Q = Transitional Voltage R = Usual Arc Voltage• In AC Welding (e.g. MMAW), the polarity alternates every half cycle.• Welding current becomes null at the crossover. The arc once extinguishes at the crossover and reignites in the following half cycle. This arc voltage is called reignition voltage, P.• The reignition voltage, P is higher than both a transitional arc voltage, Q and the usual arc voltage, R.• In an open circuit voltage of a power source, Po must be higher than the reignition voltage, P for AC arc to be sustained. Welding for Engineers 26
  27. 27. Influence of Shielding Gas Type over Metal Transfer Globular Transfer Spray Transfer Welding for Engineers 27
  28. 28. Mode of Droplet Transfer in Consumable Electrode Welding Welding for Engineers 28
  29. 29. Classification of Molten Metal Transfer Mode Welding current – Low With Active Gas (CO2) – Unstable With Active Gas (CO2) – Stable With Inert Gas (Argon) Welding for Engineers 29
  30. 30. Welding Condition and Droplet Transfer Mode 27% Welding for Engineers 30
  31. 31. Effective Factors on Weld Penetration Welding for Engineers 31
  32. 32. Effect of Welding Condition on Bead FormationLow Current High CurrentHigh Speed High Speed High Current Low Speed Welding for Engineers 32
  33. 33. Characteristics of Power Source Drooping – Manual Welding Constant – Automatic or Semi-Automatic (high current – self regulation(a) Mechanism of Arc Stability in a (b) Mechanism of Arc Stability in a Welding Power Source with drooping Constant voltage characteristics Characteristics welding power source Welding for Engineers 33
  34. 34. Important Actions of Arc Plasma(1) Magnetic pinch effect • Droplet transfer(2) Magnetic arc blow • Magnetized base metal • DC currents (arc stiffness)(3) Plasma gas flow • Electro-Magnetic interaction(4) Thermal pinch effect • Stability as plasma phase(5) Cleaning action ( on cathode ) • Reduction of oxides(6) Heat input ( on anode ) • Anode > Cathode, due to work function of the material(7) Digging action • By the pressure of Arc Plasma Welding for Engineers 34
  35. 35. Exercise 1:Which are the gas shielded metal arc welding ? • Shielded metal arc welding • MAG, MIG welding • TIG welding • Electro-gas arc welding • Submerged arc welding • Self-shielded arc welding • Plasma arc welding • Stud arc welding Welding for Engineers 35
  36. 36. Exercise 2. Arrange following welding processes in the below table. a. Arc welding b. Brazing c. Cold pressure welding d. Electron beam welding e. Explosion welding f. Flash welding g. Friction welding h. Gas welding i. Laser welding j. Resistance welding k. Riveting l. Soldering m. Thermit weldingJoining Energy Electrical Energy Chemical Energy Mechanical Energy Light EnergyJoining MechanismMechanical JoiningWelding Processes Fusing Welding Pressure Welding Brazing/Soldering Welding for Engineers 36
  37. 37. Arc Welding Equipment Welding for Engineers 37
  38. 38. External Characteristics of Welding Power Source & Operation Pointe.g. SMAW, SAW e.g. TIG, PAW e.g. GMAW (MAG & MIG) Welding for Engineers 38
  39. 39. Self-Regulation of Arc Length by Constant Voltage Characteristic Welding Power Source WF: Electrode Fee rate MR: Electrode Melting Rate WF = Constant, I1 < Io < I2 Welding for Engineers 39
  40. 40. Movable-Shunt-Core AC Welding Power Source Welding for Engineers 40
  41. 41. Working Principle of Movable-Shunt-Core AC Welding Power Source High CurrentVoltage-AmpereCharacteristic ofArc Low Current Welding for Engineers 41
  42. 42. Thyristor Controlled Welding Power Source Welding for Engineers 42
  43. 43. Inverter Controlled Welding Power Source Welding for Engineers 43
  44. 44. Advantages of Inverter Controlled Power Source Welding for Engineers 44
  45. 45. Schematic Diagram of Inverter Controlled AC Welding Power Source This is especially suitable for TIG welding of aluminium and its alloy Welding for Engineers 45
  46. 46. Handling of Welding Power Source A welding power source must ne be used continuously for a long time without care! Rated Welding Current (A) 2Allowable Cycle (%) = x Rated Duty Cycle (%) Max Welding Current of Usage(A) For Example: When a power source of a rated output 350A and a rated duty cycle 60% is used at 300A, the allowable duty cycle is given as below. 350(A) 2 Allowable Cycle (%) = x 60(%) = 82% 300 (A) Welding for Engineers 46
  47. 47. Allowable Duty Cycle of Welding Power Source Welding for Engineers 47
  48. 48. For example: The max welding current for continuous welding (Im) is a welding current with which continuous welding can apply without burn out of a welding power source In the case of rated output of 350A and rated duty cycle of 60%. . Im can also be calculated as below. 350(A) 2 100(%) = x 60(%) Im (A) √ Im = 350 (A) x 60% = 271 (A) 100%Thus, Consequently, the power source does not get burnt out at continuouswelding as far as the power is used at an output current below 270A. Welding for Engineers 48
  49. 49. Effect of Welding Lead Length on Arc Stability Welding for Engineers 49
  50. 50. Exercise 3:Fill in all the technical terms – Welding Processes(a) Sketch of a Weld Joint (b) Welding Positions Welding for Engineers 50
  51. 51. Arc Welding– Shielded Metal Arc Welding (SMAW or MMAW)– GMAW (MAG & MIG) Welding– TIG Welding– Electrogas Arc Welding– Submerged Arc Welding– Self-Shielded Arc Welding– Plasma Arc Welding– Stud Arc Welding Welding for Engineers 51
  52. 52. Shielded Metal Arc Welding – SMAW Manual Metal Arc Welding – MMAW• Several types of covered electrodes• Coated flux dissolved – Generate gasses  Stable arc – Make slag  De-oxidation and shield weld metal Welding for Engineers 52
  53. 53. Set-up of Manual Metal Arc Welding (MMAW) Equipment Welding for Engineers 53
  54. 54. Characteristics of MMAW or SMAWDiameter of electrode – 3.2mm to 6.4mmWelding current – 100A to 2,000AWelding power source – A moveable-shunt-core typeWhen arc length becomes higher, the electrode feed speed is increased toshorten the arc length.The arc length is autogenously controlled constant with self-regulating ofarc by a constant voltage power source. Advantages: Limitations: (1) Highly efficient welding with (1) Limited welding position – flat & high welding current. horizontal (2) Deep penetration of weld (2) Limited weld line of linear, of semi- (3) Unnecessary of an arc linear and of large radius curve protector for optical radiation (3) No applicability to weld complex line (4) Rare spatter and fume (4) Requirements of strict groove (5) Little disturbance from wind preparation (5) Heat affected zone (HAZ) softened or embrittled by large heat input (6) Relatively expensive machine Welding for Engineers 54
  55. 55. Arc Welding– Shielded Metal Arc Welding (SMAW or MMAW)– GMAW (MAG & MIG) Welding– TIG Welding– Electrogas Arc Welding– Submerged Arc Welding– Self-Shielded Arc Welding– Plasma Arc Welding– Stud Arc Welding Welding for Engineers 55
  56. 56. Set-up of Gas-Shielded Metal Arc Welding Equipment Welding for Engineers 56
  57. 57. Gas Metal Arc Welding (MAG & MIG)MAG: Metal Active Gas (CO2 or CO2+Ar)MIG: Metal Invert Gas (Ar)Schematic View of MAG Welding MAG Welding Equipment Welding for Engineers 57
  58. 58. Periodic Table Welding for Engineers 58
  59. 59. Balance of Wire Feed Rate and Wire Melting Rate Welding for Engineers 59
  60. 60. Control of Welding Current Waveform in MAG Welding(a) Increasing rate control of short circuiting current (e) Retarding control of increasing timing for short(b) Suppression of short circuiting current circuiting current(c) Decreasing rate control of arc current (f) Breaking current control of the short circuiting(d) Promotion of short circuiting (g) Suppression of arc reignition current Welding for Engineers 60
  61. 61. Pulsed Gas-Shielded Metal Arc (Pulsed-MAG & Pulsed-MIG) Welding(a) A peak current and a base current repeat at a given pulse frequency.(b) The peak current level is chosen to be higher than a transition current for spray transfer.(c) A droplet is transferred by strong electromagnetic pinch force at a given time.(d) Sputter rarely occurs in a spray transfer mode as there is no short circuiting happened. Welding for Engineers 61
  62. 62. Droplet Transfer Diagram of MIG Welding  Cross Section Shape of Bead Buried Arc Welding for Engineers 62
  63. 63. Effect of Pulsed Current on the transfer Pulsed Current Waveform Welding for Engineers 63
  64. 64. Power sources for weldingAC arc welding power sources• Movable iron core / Movable coil type• Thyristor type• Inverter typeDC arc welding power sources• Engine or motor driven generator type• Thyristor type• Inverter type Welding for Engineers 64
  65. 65. Comparison of DC and AC Welding Power Sources DC Welding Power Source AC Welding Power Source Thyristor Inverter Single Phase Inverter Controlled Controlled Transformer Controlled Open Circuit Low Low High Low VoltageStability of Arc Good Excellent Poor GoodMagnetic Arc Often Occurs Often Occur Hardly Occurs Hardly Occurs Blow Power Factor High Very High Low Very High Welding for Engineers 65
  66. 66. Arc Welding– Shielded Metal Arc Welding (SMAW or MMAW)– GMAW (MAG & MIG) Welding– TIG Welding (GTAW)– Electrogas Arc Welding– Submerged Arc Welding– Self-Shielded Arc Welding– Plasma Arc Welding– Stud Arc Welding Welding for Engineers 66
  67. 67. Set-up of TIG Welding Equipment Welding for Engineers 67
  68. 68. Characteristics of TIG WeldingA filler metal (a rod or a wire) must be added when deposited metal isnecessary.Separate addition of a filler material means that welding heat input andamount of deposited metal can be controlled separately.Advantages Limitations(1) All positional welding is possible. (1) Slow welding speed(2) Easiness of bead formation at a (2) Low efficiency root pass. (3) Expensive shielding gas of argon(3) Highly clean weld metal of and helium excellent toughness, elongation and anti-corrosion.(4) Availability of clean bead surface – no oxidation(5) No necessity of removal of slag(6) Applicable to all metals Welding for Engineers 68
  69. 69. TIG Welding (Tungsten Invert Gas Welding) Welding for Engineers 69
  70. 70. Ignition Methods of TIG Arc and Their Characteristics Welding for Engineers 70
  71. 71. Pulsed TIG WeldingIp: Peak Current Ib: Base CurrentTp: Peak Time Tb: Base Current TimeT: Pulse Time (= Tp + Tb)f = Pulse frequency (=1/T = 1/Tp + Tb) Welding for Engineers
  72. 72. Effect of Electrode Polarity in TIG Welding Welding for Engineers 72
  73. 73. Effect of EP Time Ratio Control Welding for Engineers 73
  74. 74. Arc Welding– Shielded Metal Arc Welding (SMAW or MMAW)– GMAW (MAG & MIG) Welding– TIG Welding– Electrogas Arc Welding (EGW)– Submerged Arc Welding– Self-Shielded Arc Welding– Plasma Arc Welding– Stud Arc Welding Welding for Engineers 74
  75. 75. Electrogas Arc Welding – EGW Welding for Engineers 75
  76. 76. Characteristics of EGW• EGW fundamentally applies in single pass welding.• Thickness of plates – 10 to 35mm; for heavy thickness, oscillating torch or multi-pass welding can be used.• Applications – for butt joints in vertical up position in a ship hull, a storage tank, a pressure vessel, a bridge, ..etcAdvantages Limitations(1) High work efficiency because of (1) Deterioration of mechanical properties high welding current. of joints because of large heat input.(2) Little angular distortion because (2) Long starting time after the of a small number of passes. interruption of welding(3) Large tolerance in groove (3) Applicability only to the vertical up preparation and in groove set up. position Welding for Engineers 76
  77. 77. Arc Welding– Shielded Metal Arc Welding (SMAW or MMAW)– GMAW (MAG & MIG) Welding– TIG Welding– Electrogas Arc Welding– Submerged Arc Welding– Self-Shielded Arc Welding– Plasma Arc Welding– Stud Arc Welding Welding for Engineers 77
  78. 78. Submerged Arc Welding – SAW Welding for Engineers 78
  79. 79. Side Beam with Submerged Arc Welding Equipment Welding for Engineers 79
  80. 80. Arc Welding– Shielded Metal Arc Welding (SMAW or MMAW)– GMAW (MAG & MIG) Welding– TIG Welding– Electrogas Arc Welding– Submerged Arc Welding– Self-Shielded Arc Welding (FCAW-S)– Plasma Arc Welding– Stud Arc Welding Welding for Engineers 80
  81. 81. Self-Shielded Arc Welding (FCAW-S) Welding for Engineers 81
  82. 82. Self-Shield Arc Welding Welding for Engineers 82
  83. 83. Characteristics of FCAW-S• Arc length to keep as short as possible to secure the shielding.• Longer stick out aiming to preheat flux in the electrode.• Retract start of arc to eliminate defects.• Applications: welding of steel structures, steel pipe piles, ..etcAdvantages Limitations(1) No necessity of preparation of (1) Large volume of fume with some wire. shielding gas. (2) Deterioration of mechanical properties(2) Easy handling of welding torch by and occurrence of blowholes caused by its light weight. insufficient control of the arc length.(3) Less disturbance from wing (3) Shallow penetration. Welding for Engineers 83
  84. 84. Exercise 4.Which type of power sources are used for followingprocesses ?Fill in either AC or DC in the ( ).a. Shielded (Manual ) Metal Arc Welding ( )b. MIG/MAG Welding ( )c. CO2 Gas Arc Welding with Flux Cored Wire ( )d. TIG for aluminum alloys ( ) Welding for Engineers 84
  85. 85. Arc Welding– Shielded Metal Arc Welding (SMAW or MMAW)– GMAW (MAG & MIG) Welding– TIG Welding– Electrogas Arc Welding– Submerged Arc Welding– Self-Shielded Arc Welding (FCAW-S)– Plasma Arc Welding (PAW)– Stud Arc Welding Welding for Engineers 85
  86. 86. Plasma Arc Welding Welding for Engineers 86
  87. 87. Comparison of TIG and Plasma Arcs Welding for Engineers 87
  88. 88. Electron Beam Welding (EBW) Welding for Engineers 88
  89. 89. Set-up of Electron Beam Welding Equipment Welding for Engineers 89
  90. 90. Characteristics of EBW• Electrons, emitted from a heated cathode, are accelerated in high voltage and are converged to a high energy density electron beam with a magnetic coil.• The electron beam is projected onto a workpiece in vacuum.• A deflection coil is used to irradiate the beam onto a welding position of the workpiece.• Energy density of the electron beam reaches to more than thousands times of that TIG arc.• High quality welding with high efficiency. Advantages Limitations (1) Deep penetration with small heat (1) Necessity of vacuum. input. (2) Precise preparation of a groove face. (2) Narrow heat affected zone and less (3) Expensive equipment deterioration of base metal. (3) Small weld strain and deformation Welding for Engineers 90
  91. 91. Laser Beam Welding (LBW) Welding for Engineers 91
  92. 92. Characteristics of Laser Beam Welding (LBW) • A welding method uses a laser light beam as heat source. • Laser light is photons of the same wavelength in a synchronized phase. • Laser is focused with mirrors or lenses onto a workpiece. • Energy density of laser reaches to more than thousands times of that of arc, like an electron beam as depicted below.Advantages Limitations(1) Possibility of welding in an atmosphere. (1) Dependence of light absorption upon(2) No influence from magnetic field. surface conditions of a workpiece.(3) Possibility of welding non-metallic (2) Safety protection from laser light. materials. (3) Low energy efficiency esp at a laser generator. (4) Expensive instruments. Welding for Engineers 92
  93. 93. Set-up of Laser Beam Welding Equipment (A)CO2 Gas Laser– Use a continuous wave mode and wavelength is 10.6µm.– An optical fibre cannot pass through the 10.6µm wave.– Mirrors are used to convey the light.– Laser gas: a mixture of helium, nitrogen and CO2, circulated for reuse and also deteriorated during services. Welding for Engineers 93
  94. 94. Set-up of Laser Beam Welding Equipment (B)YAG Laser– Can generate both a pulse wave and a continuous wave.– The light is oscillated in a YAG rod excited by Kr arc lamps, Xe arc lamps or lights of diode laser (LD).– The wavelength is 1.03µm or 1.06µm; the light can pass through an optical fibre.– An optical fibre is used for transmission. Welding for Engineers 94
  95. 95. Duty cycleElectric Energy/sec =VI = RI 2Power = Energy / sec (J/s, VA, W)( When IActual is different from IRated , duty cycle must be changed. )Actual power for welding < Rated power for welding 2 rActual Duty Cycle R(I Actual) < r Rated Duty Cycle R(I Rated)2 2 I Rated rActual Duty Cycle < r Rated Duty Cycle IActual 2 Rated Secondary Welding CurrentAllowable Duty Cycle (%) = X Rated Duty Cycle (%) Actual Welding Current Welding for Engineers 95
  96. 96. Exercise 5:Rated duty cycle: 40%Rated secondary welding current: 400A.When the welding current is 300A, how much duty cycle isallowable ? Welding for Engineers 96

×