An introduction to various welding processes, suitable for all welding students and welding professionals like welder, supervisor, inspector, engineer.
2. 2
Overview of joining methods
Mechanical methods
Screwed fasteners, rivets,
Adhesive bonding
Brazing and Soldering
Base metal does not fuse.
Molten filler drawn into close-fit joints by capillary
action (surface tension forces).
Brazing filler melts >450 C, solder <450 C
Welding
Introduction to welding
3. 3
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
Introduction to welding
4. 4
Welding processes
Fusion welding
Welding in the liquid state with no pressure
Union is by molten metal bridging
Solid phase welding
Carried out below the melting point without filler
additions
Pressure often used
Union is often by plastic flow
Introduction to welding
5. 5
Introduction to welding
Basic Requirements of Welding Process
Source of Heat
Chemical Reaction
Electrical - Arc, Resistance, Induction
Vacuum
Mechanical
Protection from Atmosphere
Gas Shielding
Flux
Mechanical Expulsion
6. 6
Fusion welding heat sources
Power beams
Laser
Electron beam
Spot, seam and
projection welding
Electroslag
Electric arcChemical reactionElectric resistance
Oxyfuel gas
welding
Thermit welding
MMAW
GMAW
GTAW
FCAW
SAW
Introduction to welding
9. 9
The electric arc
Electric discharge between 2
electrodes through ionised
gas
10 to 2000 amps at 10 to
500 V arc voltage
Column of ionised gas at high
temperature
Forces stiffen the arc column
Transfer of molten metal
from electrode to workpiece
Can have a cleaning action,
breaking up oxides on
workpiece
+
- Cathode
drop zone
Anode
drop zone
Peak
temperatures
18,000 K
Introduction to welding
10. 10
Arc energy
Q = arc energy in kJ/mm
E = current in amps
I = arc voltage
V = travel speed in mm/min
Low arc energy
• Small weld pool size
• Incomplete fusion
• High cooling rate
• Unwanted phase transformations
• Hydrogen cracking
High arc energy
• Large weld pool size
• Low cooling rate
• Increased solidification cracking risk
• Low ductility and strength
• Precipitation of unwanted phases
(corrosion and ductility)
Introduction to welding
Q =
E x I
V
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
12. 12
Manual Metal Arc Welding
MMAW,
SMAW,
Stick electrode welding
Manual welding
Introduction to welding
13. 13
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
Introduction to welding
15. 15
Manual Metal Arc Welding
Minimum equipment
Power source (ac or dc, engine driven or
mains transformer)
Electrode holder and leads
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
Introduction to welding
16. 16
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
Introduction to welding
17. 17
Manual Metal Arc Welding
Covered electrodes
Core wire
Solid or tubular
2mm to 8mm diameter,
250 to 450mm long
Coating
Extruded as paste, dried
to strengthen
Dipped into slurry and
dried (rare)
Wound with paper or
chord (obsolete)
Introduction to welding
18. 18
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)
Introduction to welding
19. Manual Metal Arc Welding
AWS A5.1 classification
E XXXX - H
Useable positions
1=all positions
2=flat + horizontal
4=vertical down
Tensile Strength
in KPSI
Flux type
20 = Acidic (iron oxide)
10, 11 = Cellulosic
12, 13 = Rutile
24 = Rutile + iron powder
27 = Acidic + iron powder
16 = basic
18, 28 = basic + iron powder
Hydrogen level (HmR)
H = 5 ml / 100g of WM
R = low moisture pick-up
Introduction to welding
20. 20
Manual Metal Arc Welding
Applications
Wide range of welded products:
light structure & Heavy steel structures
Workshop and site
High integrity (nuclear reactors, pressure
equipment)
Ideal where access is difficult -
construction site, inside vessels,
underwater
Joins a wide range of materials
Introduction to welding
21. 21
Manual Metal Arc Welding
Limitations
Low productivity
Low power
Low duty cycle (frequent electrode
changes)
Hydrogen from flux coatings
Electrode live all the time
Arc strike, stray current and electric shock
risks
Introduction to welding
25. Submerged arc welding - Features
High productivity
2 to 10 kg/hour
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)
Introduction to welding
26. 26
Submerged arc welding - Equipment
Power source
Welding head and
control box
Welding head travel
Flux recovery system
(optional)
Positioners and
Fixtures
Introduction to welding
27. 27
Submerged arc welding - Consumables
Solid or cored wires
Granular fluxes
Agglomerated, fused or sintered
Alloying activity
• Contribution to weld metal chemistry from flux
Basicity
• Acid fluxes made from manganese oxide, silica, rutile are
easy to use
• Basic fluxes (MgO, CaO, CaF2, Al2O3) provide excellent
toughness welds
Introduction to welding
28. 28
Submerged arc welding - Applications
Long straight welds in heavier material
Vessel longitudinal and circumferential
welds
Flange to web joints of I beams
Flat or horizontal position
Flux has to be supported
Access has to be good
Introduction to welding
29. 29
Submerged arc welding
Process variations
Surfacing and hardfacing
Wire and strip electrodes
Semi-automatic
Multiple electrodes
2 (and more) electrode wires
From one or more power sources
Iron powder additions to groove
Introduction to welding
31. 31
Gas shielded arc process
Tungsten Inert Gas welding (TIG)
Gas tungsten arc welding (GTAW)
Introduction to welding
32. 32
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
Introduction to welding
34. 34
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)
Introduction to welding
35. 35
Gas Tungsten Arc Welding - Process features
Excellent control
Stable arc at low power (80A at 11V)
Independently added filler
Ideal for intricate welds eg root runs in pipe or thin sheet
Low productivity 0.5kg/h manual
High quality
Clean process, no slag
Low oxygen and nitrogen weld metal
Defect free, excellent profile even for single sided welds
Introduction to welding
36. Gas Tungsten Arc Welding - Equipment
Welding power source with constant
current characteristic
DC for most metals, AC for Al
Arc starting by high frequency (5000V, 0.05A)
Sequence timers for arc starting, arc finishing &
gas control
Water- or gas-cooled torch with tungsten
electrode
Electrode may contain thoria or zirconia, etc
Introduction to welding
37. 37
Gas Tungsten Arc Welding - Shielding gases
Torch is fed with an inert or reducing gas
Pure argon - widespread applications
Argon-helium - Higher arc voltage, inert
Argon-2% hydrogen - Cu alloys & austenitic steel
Torch gas must not contain oxygen or CO2
Backing (or purge) gas
Used for all single-sided welds except in carbon steel
Argon, nitrogen, formier gas (N2 + H2)
Supplementary shielding
Reactive metals: Ti, etc
Gas filled chambers or additional gas supply devices
Introduction to welding
38. 38
Gas Tungsten Arc Welding - Filler metals
Autogenous welding (no filler)
Filler wire or rod of matching composition
C-Mn & low alloy steel
Stainless Steel
Al, Mg, Ti
Cu & Ni
Consumable inserts - filler preplaced in joint
Introduction to welding
41. 41
GMAW and FCAW
Gas metal arc welding
(MIG, MAG, CO2 welding)
Flux cored arc welding
Introduction to welding
42. 42
Gas metal arc welding
A continuous solid wire, small
diameter
GMAW uses solid wire, no flux
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)
Introduction to welding
44. 44
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
Introduction to welding
Gas metal arc welding
46. 46
Gas metal arc welding - Equipment
Welding power source
Wire feeder mechanism
May be in power source cabinet
Gun with gas supply & trigger
switch
Manual (semiautomatic) guns
Automatic torches available
Can be fitted to robot etc
Introduction to welding
47. Gas metal arc welding – Metal transfer
Spray
Higher current & voltage, argon-rich gas
Short circuiting (dip)
Low current and voltage, CO2
Globular
Intermediate current
Pulsed current power sources
Adjustable frequency
One droplet per current pulse.
Introduction to welding
51. 51
Gas metal arc welding - Gas mixtures
Inert gases (MIG)
Argon or helium or mixtures of these
Active base metals, Al, Mg, Ti
Active gases (MAG and FCAW)
Carbon dioxide
Argon plus oxygen and/or carbon dioxide
Nitrogen, hydrogen
Introduction to welding
60. 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
62. 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
65. 65
Introduction to welding
Solid-State Welding
Heat
Pressure
Time
NO Melting
NO Filler Material
Intimate Contact
Usually Requires Deformation
Works with Dissimilar Metals