2. Content:
Chapter 1: Welding Processes and Equipment
Chapter 2: Materials and their Behaviours in Welding
Chapter 3: Design and Construction
Chapter 4: Fabrication and Application Engineering
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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
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9. Fusion Welding – A welding process where metal
workpieces are joined through melting (fusing) and
solidifying. Molten metal id formed by heating, and is made
up from base metal, or from mixture of base metal and filler
metal.
Pressure Welding – A welding process that forms a weld
joint by pressure of mechanical force after heating up the
joint by friction or other heat effects.
Brazing and Soldering – joining processes that form a joint
by filling gap with molten brazing filler metal after heating
the joint. Capillary force induces the filling. Brazing filler
metal has a lower melting point than that of the base metal
so that the base metal does not melt.
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12. Fusion Welding
Advantages:
(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 workforce
Limitations:
(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
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18. Characteristic of Arc
• Voltage-Current relationship
• Voltage distribution
(a) Distribution of Arc Voltage (b) Arc Characteristics
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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…
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21. Structure of Arc
• Arc Voltage is a sum of cathode drop voltage, arc column voltage
and anode drop voltage.
• Arc Column Voltage increases as Arc Length increases.
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23. Electromagnetic Pinch Effect
Electromagnetic attractive force causes the cross section of the
arc to shrink – Electromagnetic Pinch Effect.
Arc also shrinks to reduce its surface area to suppress heat loss
when the arc is cooled from ambient – Thermal Pinch Effect
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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.
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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.
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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.
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27. Influence of Shielding Gas Type over Metal Transfer
Globular Transfer Spray Transfer
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28. Mode of Droplet Transfer in Consumable Electrode Welding
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29. Classification of Molten Metal Transfer Mode
Welding current – Low
With Active Gas (CO2) – Unstable
With Active Gas (CO2) – Stable
With Inert Gas (Argon)
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32. Effect of Welding Condition on Bead Formation
Low Current High Current
High Speed High Speed
High Current
Low Speed
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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
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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
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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
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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 welding
Joining Energy
Electrical Energy Chemical Energy Mechanical Energy Light Energy
Joining Mechanism
Mechanical Joining
Welding Processes
Fusing Welding
Pressure Welding
Brazing/Soldering
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41. Working Principle of Movable-Shunt-Core AC Welding Power Source
High Current
Voltage-Ampere
Characteristic of
Arc
Low Current
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45. Schematic Diagram of Inverter Controlled AC Welding Power Source
This is especially suitable for TIG welding of aluminium and its alloy
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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) 2
Allowable 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)
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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 continuous
welding as far as the power is used at an output current below 270A.
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49. Effect of Welding Lead Length on Arc Stability
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50. Exercise 3:
Fill in all the technical terms – Welding Processes
(a) Sketch of a Weld Joint (b) Welding Positions
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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
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53. Set-up of Manual Metal Arc Welding (MMAW) Equipment
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54. Characteristics of MMAW or SMAW
Diameter of electrode – 3.2mm to 6.4mm
Welding current – 100A to 2,000A
Welding power source – A moveable-shunt-core type
When arc length becomes higher, the electrode feed speed is increased to
shorten the arc length.
The arc length is autogenously controlled constant with self-regulating of
arc 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
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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
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59. Balance of Wire Feed Rate and Wire Melting Rate
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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
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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.
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62. Droplet Transfer Diagram of MIG Welding
Cross Section Shape of Bead
Buried Arc
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63. Effect of Pulsed Current on the transfer
Pulsed Current Waveform
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64. Power sources for welding
AC arc welding power sources
• Movable iron core / Movable coil type
• Thyristor type
• Inverter type
DC arc welding power sources
• Engine or motor driven generator type
• Thyristor type
• Inverter type
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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
Voltage
Stability of Arc Good Excellent Poor Good
Magnetic Arc
Often Occurs Often Occur Hardly Occurs Hardly Occurs
Blow
Power Factor High Very High Low Very High
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67. Set-up of TIG Welding Equipment
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68. Characteristics of TIG Welding
A filler metal (a rod or a wire) must be added when deposited metal is
necessary.
Separate addition of a filler material means that welding heat input and
amount 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
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70. Ignition Methods of TIG Arc and Their Characteristics
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71. Pulsed TIG Welding
Ip: Peak Current Ib: Base Current
Tp: Peak Time Tb: Base Current Time
T: Pulse Time (= Tp + Tb)
f = Pulse frequency (=1/T = 1/Tp + Tb)
Welding for Engineers
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, ..etc
Advantages 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
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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, ..etc
Advantages 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.
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84. Exercise 4.
Which type of power sources are used for following
processes ?
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 ( )
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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
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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.
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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.
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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.
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95. Duty cycle
Electric Energy/sec =VI = RI 2
Power = 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 Current
Allowable Duty Cycle (%) = X Rated Duty Cycle (%)
Actual Welding Current
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96. Exercise 5:
Rated duty cycle: 40%
Rated secondary welding current: 400A.
When the welding current is 300A, how much duty cycle is
allowable ?
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