Welding course NPTEL · Plasma arc welding Tungsten electrode Plasma gas Shielding gas Power supply...
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![Page 1: Welding course NPTEL · Plasma arc welding Tungsten electrode Plasma gas Shielding gas Power supply ... Ref: Welding Metallurgy, 2nd Edition by Sindo Kou, Wiley-Interscience ISBN:](https://reader031.fdocuments.us/reader031/viewer/2022020204/5b7c171f7f8b9a28438bcde2/html5/thumbnails/1.jpg)
Introduction
Online course on Analysis and Modelling of Welding
G. PhanikumarDept. of MME, IIT Madras
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Classification of Manufacturing Processes
ManufacturingProcesses
CastingProcesses
FormingProcesses
MachiningProcesses
JoiningProcesses
Ingot CastingShape CastingPower Metallurgy
ForgingExtrusionSheet Metal Forming
Turning, BoringDrilling, MillingGrinding
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Classification of Joining Processes
Joining Processes
MechanicalFastening
AdhesiveJoining
Brazing
Welding
Soldering
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Different Welding Processes
WeldingProcesses
Arc Welding:SMAW, GMAW,
GTAW, SAW, FCAW, PAW
Resistance Welding:Spot, Seam, Projection
Beam Processes:LBW, EBW
Solid state Welding:
USW, FRW, EXW
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Five basic joint designs
BUTTLAP TEE
CORNEREDGE
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Four basic types of fusion welds
Bead / Surface Weld Groove Weld
Fillet Weld Plug Weld
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Bead / Surface Welds
• For butt welds
• No edge preparation
• Thin sheets of metal
• Building up surfaces
• Weld overlay
Bead / Surface Weld
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Groove Welds
Groove Weld
• For butt welds
• Thicker materials
• Full thickness welding
• Detailed edge preparation
• Multi-pass welding
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Groove preparations
Ref: Wikipedia, public domain. Contributedby Benrunge
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Fillet Welds
Fillet Weld
• For Tee, Lap and Corner joints
• No edge preparation
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Plug Welds
Plug Weld
• Hole drilled on thetop sheet
• To replace bolts and rivets
• When excess deposit is not desirable by design
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Five Welding Positions
gOverhead
Flat
VerticalUp Vertical
Down
Arrow shows the direction of motion of the electrode / torch. The torch is held approximately normal to this direction.
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Classification of Welding
FusionWelding
Autogenous
FillerConsumable
Electrode
Non-consumableElectrode
Flux protected
Inert gas protected
Single Pass
Multi Pass
Homogeneous
Heterogeneous
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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)
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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
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Electric Arc
• 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 between the two electrodes
Electrode
Workpiece
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Role of gases in arc welding
• Inert / active
• Shielding effect
• Stability of arc
Gas Ionization Potential
CO2 14.4 eV
O2 13.2 eV
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
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Arc characteristics
Longer Arc
Shorter Arc
OCVV
olt
age
Current
Normal operating range
Ref: Principles of Welding Technology, 3rd Edition by L. M. Gourd, ISBN: 8176490296
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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.
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Workpiece Workpiece Workpiece
DCEN DCEP AC
+
+
++
+
+
+
+
+-
-
--
-
-
--
-
70% Heat to workpiece30% Heat to Electrode
30% Heat to workpiece70% Heat to ElectrodeSurface Cleaning
50% Heat to workpiece50% Heat to ElectrodeSurface cleaning half-the-time
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Temporal profiles
Balanced Sine Wave Unbalanced Sine Wave Square Wave
SP
RP
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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.
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Shielded metal arc welding
Power source
and controls
Work cable
Electrode cable
Electrode holder
Electrode
Work
Arc
Solidified slag
Weld metal
Arc
Base metal
ElectrodeCoating
Shielding gas
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What is in the Flux?
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
Role of a Flux : Protection, Deoxidation, Stabilization and Metal Addition
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Gas metal arc welding
Travel
Base metal
Molten weld metalSolidified weld metal
Arc
Nozzle
Shielding gas
Shielding gas
Solid wire electrode
Current conductor
Feed control
Control system
Gas out
Gun control
Work piece
Wire feed drive motor
Wire
Gun
Gas in
Voltage control
Welding machine
Shielding gas source
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GMAW
Photographs from the facilities in Materials Joining Laboratory, Department of MME, IIT Madras
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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
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Gas tungsten arc welding
Travel
Filler wire
Molten weld metal
Tungsten electrode
Arc
Solidified weld
Cooling water supply
Torch
Work piece
Foot pedal (optional
Drain
Inert gas supply
AC or DC Welder
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TIG
Photographs from the facilities in Materials Joining Laboratory, Department of MME, IIT Madras
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Plasma arc weldingTungsten electrode
Plasma gas
Shielding gas
Power supply
Power supply
Work pieceTransferred arc Non transferred arc
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PAW
Photographs from the facilities in Materials Joining Laboratory, Department of MME, IIT Madras
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Submerged Arc welding
Voltage and current control
Ground
Work piece
Contact tube
Wire feed motor
Unused flux recovery tube
Flux hopper
Wire reel
Granular flux covers the weld and the arc
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SMAW
Photographs from the facilities in Materials Joining Laboratory, Department of MME, IIT Madras
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Upper column
Column
valveElectromagnetic lens
Deflection coil
Workpiece
High voltage insulator
Electron gun
To high vacuum
Vacuum
chamber
to vacuum
Schematic of a typical EBW gun
Electron beam welding
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Reflection
mirror
Half mirror
Focusing
lens
Workpiece
Cavity tube
Laser
element Xe lamp
Laser beam
Basic features of an Nd : YAG laser
Laser beam welding
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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
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Heat input vs power density
Gas Welding processes
Arc welding processes (GMAW, GTAW, etc.)
High energy beam welding processes (EBW, LBW)
Hea
t in
pu
t to
wo
rk p
iece
Power density of heat source
More damage to work piece
Higher penetration,Welding speed,Weld qualityCapital cost
Ref: Welding Metallurgy, 2nd Edition by Sindo Kou, Wiley-Interscience ISBN: 0471434914
Less damage to work piece
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Summary of featuresFeature/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 gas
Vacuum
Rate of Heat Input
Medium Medium High High Very High
Aspect Ratio of Weld
1 1 3 5 20
Max Penetration 3 mm 5 – 10 mm Up to 20 mm 25 mm 150 mm
Advantages High quality weld Continuous and Automated
Longer arc length Any location where light can reach, high speed, accuracy
Precision, accuracy, deep and narrowwelds
Materials Joined Most common metals
Most common metals
Most common metals
Reflectivity Issues Vacuum Issues
Ref: Materials and Processes in Manufacturing, 9th Edition by E. Paul DeGarmo et al., Wiley. ISBN: 9812530703
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End of Introduction