Introduction
Online course on
Analysis and Modelling of Welding
G. Phanikumar
Dept. of MME, IIT Madras
Classification of Manufacturing Processes
Manufacturing
Processes
Ingot Casting Casting Machining Turning, Boring
Shape Casting Drilling, Milling
Power Metallurgy
Processes Processes Grinding
Forming Joining
Forging Processes Processes
Extrusion
Sheet Metal Forming
Classification of Joining Processes
Joining
Processes
Mechanical
Soldering
Fastening
Adhesive
Brazing
Joining
Welding
Different Welding Processes
Welding
Processes
Arc Welding: Solid state
SMAW, GMAW, Welding:
GTAW, SAW, USW, FRW, EXW
FCAW, PAW
Resistance Welding: Beam Processes:
Spot, Seam, Projection LBW, EBW
Five basic joint designs
BUTT
LAP TEE
CORNER
EDGE
Four basic types of fusion welds
Bead / Surface Weld Groove Weld
Fillet Weld Plug Weld
Bead / Surface Welds
• For butt welds
• No edge preparation
Bead / Surface Weld
• Thin sheets of metal
• Building up surfaces
• Weld overlay
Groove Welds
• For butt welds
• Thicker materials
Groove Weld
• Full thickness welding
• Detailed edge
preparation
• Multi-pass welding
Groove preparations
Ref: Wikipedia, public domain. Contributed
by Benrunge
Fillet Welds
• For Tee, Lap and Corner
joints
Fillet Weld • No edge preparation
Plug Welds
• Hole drilled on the
top sheet
• To replace bolts and Plug Weld
rivets
• When excess deposit is
not desirable by design
Five Welding Positions
Flat
g Vertical
Overhead
Up Vertical
Down
Arrow shows the direction of motion of the electrode / torch.
The torch is held approximately normal to this direction.
Classification of Welding
Autogenous
Consumable Homogeneous
Electrode Filler
Heterogeneous
Non-consumable
Electrode Fusion
Welding
Single Pass
Flux protected
Inert gas Multi Pass
protected
Some terminology
• Traverse rate : velocity of the welding source : m/s
• Heat Input : ratio of power to velocity : J/m
• Rate of heat input or heat intensity : W/m2
• Heat intensity distribution : Q(x,y)
Overview of few welding processes
SMAW : Shielded (Manual) Metal Arc Welding
GMAW: Gas Metal Arc (MIG) Welding
GTAW: Gas Tungsten Arc (TIG) Welding
PAW: Plasma Arc Welding
SAW: Submerged Arc Welding
EBW: Electron Beam Welding
LBW: Laser Beam Welding
Electric Arc
Electrode
• Generated between two
conductors of electricity, upon
application of voltage and
separated by a small distance
• Presence of ionisable gas
• Sustained electric discharge
through ionized gas column Workpiece
between the two electrodes
Role of gases in arc welding
• Inert / active Gas Ionization Potential
CO2 14.4 eV
• Shielding effect O2 13.2 eV
• Stability of arc N2 14.5 eV
H2 13.5 eV
Ar 15.7 eV
He 24.5 eV
Ref: Welding Metallurgy, 2nd Edition by Sindo Kou, Wiley-Interscience ISBN: 0471434914
Arc characteristics
OCV
Longer Arc
Shorter Arc
Voltage
Normal operating range
Current
Ref: Principles of Welding Technology, 3rd Edition by L. M. Gourd, ISBN: 8176490296
Electrode Polarities
• Direct Current Straight Polarity (DCSP) : Electrode is negative.
Deeper penetration.
• Direct Current Reverse Polarity (DCEP) : Electrode is positive.
Enhanced deposition rate for consumable electrode.
• Alternating Current (AC) : Polarity is switched at a frequency.
DCEN DCEP AC
+ -
+ - + -
+ -
+ - + -
- + - -
+ +
Workpiece Workpiece Workpiece
70% Heat to workpiece 30% Heat to workpiece 50% Heat to workpiece
30% Heat to Electrode 70% Heat to Electrode 50% Heat to Electrode
Surface Cleaning Surface cleaning half-the-time
Temporal profiles
SP
RP
Balanced Sine Wave Unbalanced Sine Wave Square Wave
Spatial-temporal characteristics of arc
• Voltage, Current, Efficiency
• Wave form : flat, square, sine, unbalanced sine etc.
• Pulsing effects (Peak value, base value)
• Frequency (Hz)
• Traverse rate (m/s)
• Electrode path : arc oscillation, frequency and amplitude etc.
Shielded metal arc welding
Electrode holder
Power
source
and
controls Arc Shielding gas
Coating Electrode
Electrode
Work cable
Arc
Work
Solidified slag
Electrode cable
Weld metal
Base metal
What is in the Flux?
Role of a Flux : Protection, Deoxidation, Stabilization and Metal Addition
Constituent Role
Iron oxide Slag former, arc stabilizer
Titanium oxide Slag former, arc stabilizer
Calcium fluoride Slag former, fluxing agent
Potassium silicate Arc stabilizer, Binder
Magnesium oxide Fluxing agent
Cellulose Gas former
Calcium carbonate Gas former, Arc stabilizer
Ferro-manganese, Ferro-chrome Alloying changes
Ferro-silicon Deoxidizer
Feed control Gas metal arc welding
Control system
Wire
Gas out Shielding gas source Shielding gas
Solid wire electrode
Gun Current conductor
control Travel
Gas in
Shielding gas
Nozzle
Gun
Voltage
control
Arc
Work piece
Welding machine Base metal
Wire feed drive motor
Solidified weld metal Molten weld metal
GMAW
Photographs from the facilities in
Materials Joining Laboratory,
Department of MME, IIT Madras
Metal transfer modes
• Globule transfer
– Droplets close to or larger than diameter of the electrode
– Reach base material by gravity
– Leads to spatter
• Spray transfer
– Fine droplets
– Reach base material by EM force
• Short-circuit transfer
– Small and fast solidifying weld pools
Gas tungsten arc welding
Inert gas supply
Cooling water supply
AC or DC Welder Travel
Drain
Torch
Filler wire
Tungsten
electrode
Work piece
Arc Molten weld metal
Foot pedal (optional Solidified weld
TIG
Photographs from
the facilities in
Materials Joining
Laboratory,
Department of MME,
IIT Madras
Plasma arc welding
Tungsten electrode
Plasma gas
Shielding gas
Power supply
Power supply
Work piece Non transferred arc
Transferred arc
PAW
Photographs from the
facilities in Materials
Joining Laboratory,
Department of MME,
IIT Madras
Submerged Arc welding
Wire reel
Flux hopper
Unused flux recovery tube
Wire feed
motor
Contact tube Voltage and current control
Work piece Granular flux covers the
weld and the arc
Ground
SMAW
Photographs from the
facilities in Materials
Joining Laboratory,
Department of MME,
IIT Madras
Electron beam welding
High voltage insulator
Upper column
Electron gun
Column
valve
Electromagnetic lens
To high vacuum
Deflection coil
Vacuum to vacuum
chamber
Workpiece
Schematic of a typical EBW gun
Laser beam welding
Cavity tube
Half mirror
Workpiece
Focusing
lens
Reflection
mirror
Laser beam
Laser
element Xe lamp
Basic features of an Nd : YAG laser
Intensity of heat sources
Process Heat source intensity
(W/m2)
SMAW, FCAW 5x106 – 5x108
GTAW, GMAW 5x106 – 5x108
PAW 5x106 – 1010
LBW, EBW 1010 – 1012
Ref: Principles of Welding by Robert W. Messler, Wiley-VCH (2004) ISBN: 0471253766
Heat input vs power density
More damage to
work piece
Gas Welding processes
Heat input to work piece
Arc welding processes (GMAW, GTAW, etc.)
Higher penetration,
Welding speed,
Weld quality
Capital cost
High energy beam welding processes (EBW, LBW)
Less damage to
work piece
Power density of heat source
Ref: Welding Metallurgy, 2nd Edition by Sindo Kou, Wiley-Interscience ISBN: 0471434914
Summary of features
Feature/Process GTAW GMAW PAW LBW EBW
Heat Source Arc Arc Plasma Arc Laser beam Electron beam
Protection Shielding gas Shielding gas Shielding gas None / Shielding Vacuum
gas
Rate of Heat Medium Medium High High Very High
Input
Aspect Ratio of 1 1 3 5 20
Weld
Max Penetration 3 mm 5 – 10 mm Up to 20 mm 25 mm 150 mm
Advantages High quality weld Continuous and Longer arc length Any location Precision,
Automated where light can accuracy, deep
reach, high and narrow
speed, accuracy welds
Materials Joined Most common Most common Most common Reflectivity Issues Vacuum Issues
metals metals metals
Ref: Materials and Processes in Manufacturing, 9th Edition by E. Paul DeGarmo et al., Wiley. ISBN: 9812530703
End of Introduction
