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PRESENTATION BY: HARDISH TRIVEDI
1
Gas Metal Arc Welding
By Hardish Trivedi
PRESENTATION BY: HARDISH TRIVEDI
2
What Is GMAW ?• A Fusion Welding Process – Semi Automatic• Arc Between Consumable Electrode &Work• Arc Generated by Electric Energy From a Rectifier
/ Thyrester / Inverter• Filler Metal As Electrode Continuously fed From
Layer Wound Spool. • Filler Wire Driven to Arc By Wire Feeder through
Welding Torch• Arc & Molten Pool Shielded by Inert Gas through
Torch / Nozzle
PRESENTATION BY: HARDISH TRIVEDI
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Gas Metal Arc Welding• MIG – Shielding Gas Ar / Ar + O2 / Ar + Co2
• MAG – Shielding Gas Co2
• FCAW – Shielding Gas Co2 With Flux cored Wire
Note:- Addition of 1 – 5% of O2 or 5 – 10% of Co2 in Ar. increases wetting action of molten metal
PRESENTATION BY: HARDISH TRIVEDI
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Power Source For MIG / MAG
• Inverter- DC
• Thyristor – DC
• Diesel Generator – DC
• Rectifier – DC
PRESENTATION BY: HARDISH TRIVEDI
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Characteristic Of GMAW Power Source
Constant V / Linier Characteristic
Appx. Horizontal Curve
V1V2
A1 A2A
V
PRESENTATION BY: HARDISH TRIVEDI
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Current & Polarity
DC- Electrode +Ve
Stable Arc
Smooth Metal Transfer
Relatively Low Spatter
Good Weld Bead Characteristics
DC- Electrode – Ve, Seldom Used
AC- Commercially Not In use
PRESENTATION BY: HARDISH TRIVEDI
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Accessories Of GMAW
• Power Source• Wire Feed Unit• Shielding Gas Cylinder, Pressure gauges/
Regulator, Flow meter ( Heater For Co2 )
• Welding Torch • Water Cooling System (For Water cooled Torch)• Earthing Cable With Clamp
PRESENTATION BY: HARDISH TRIVEDI
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Tools For GMAW • Head Screen With DIN 13 / 14 Dark Glass• Hand Wire Brush / Grinder With Wire Wheel • Cutting Pliers• Hand Gloves • Chipping Hammer / Chisel & hammer • Spanner Set• Cylinder Key• Anti-spatter Spray• Earthing Cable With Clamp
PRESENTATION BY: HARDISH TRIVEDI
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GMAW Torch
Torch HandleSpring Conduit
JobArc
Gas Cup
Shielding Gas
Filler Wire - ElectrodeNozzle Tip
On / Off Switch
PRESENTATION BY: HARDISH TRIVEDI
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Equipment & Accessories
+ –
Wire Inside Spring Lining
Flow Meter
Welding Torch Wire Feeder
Shielding Gas Cylinder
Pressure Regulator
Argon / Co2 Shielding
Power Source
With Inductance
Work
Arc–
Solenoid Valve
Copper Cup
Wire Spool
Electrode / Wire
Shielding GasHeater
(Only For Co2)
Contact Tip
Switch
Torch With Cable Max. 3Mtr
PRESENTATION BY: HARDISH TRIVEDI
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Types Of Wire Feeding In GMAW
• Push Type– Wire fed in to The torch by Pushing through Flexible
Conduit From A Remote Spool
• Pull Type– Feed Rollers Mounted on The Torch Handle Pulls the
Wire From A Remote spool
• Self Contained– Wire Feeder & The Spool On the Torch
PRESENTATION BY: HARDISH TRIVEDI
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Function Of Shielding Gas In GMAW
• Prevents Air contamination of weld Pool• Prevents Contamination During Metal
Transfer• Increases fluidity of molten metal• Minimizes the spatter generation• Helps in even & uniform bead finish
PRESENTATION BY: HARDISH TRIVEDI
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Shielding Gases For GMAW
• MIG: Argon Or Helium For SS, CS, LAS & Non-ferrous
• MIG: Ar + 1 to 2 % O2, Wire With Add. Mn & Si For SS, CS & LAS
• MIG: Ar + 5 to 20 % Co2 Wire With Add. Mn & Si For SS, CS & LAS
• MAG: Co2 With Solid Wire For CS
• FCAW: Co2 With Flux Cored Wire For CS, LAS & SS Overlay
PRESENTATION BY: HARDISH TRIVEDI
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ASME Classification For CS GMAW Wire
• SFA 5.18 : - CS Solid Wire
ER 70 S – 2, ER 70 S – 3
ER 70 S – 6, ER 70 S – 7
• SFA 5.20 :- CS Flux Cored Wire
E 71 T-1, E 71 T-2 ( Co2 Gas )
E 71 T-1M, E 71 T-2M ( Ar + Co2 Mix)
PRESENTATION BY: HARDISH TRIVEDI
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GMAW CS Wire
• Generally Copper Coated– Prevents Oxidation / rusting in Storage– Promotes Electric Conductivity in Arcing
• Available In Solid & Flux Cored– Size in mm 0.8, 1, 1.2, 1.6, 2, 2.4, 3
• Manganese & Silicon ( Mn 1 – 2 %, Si Max 1%)– Act As Deoxidizing Agents– Eliminate Porosity– Increase Wetting Of Molten Pool
PRESENTATION BY: HARDISH TRIVEDI
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Metal Transfer In MIG
• Short-Circuiting / Dip Transfer
• Globular Transfer
• Spray Transfer / Free Flight Mode
PRESENTATION BY: HARDISH TRIVEDI
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Metal Transfer In MIG
Dip/Short Circuiting Globular Spray / Free Flight
CS Solid Wire 1.2 mm Φ
Above230A
24 – 35 V
120 to 250A
16 – 24 V
Up to 120A
14 – 22V
Co2 or Ar Co2 or Ar Only Ar / Ar+O2
PRESENTATION BY: HARDISH TRIVEDI
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Short-Circuiting / Dip Transfer• Wire In Contact With Molten Pool 20 to 200 times per Second• Operates in Low Amps & Volts – Less Deposition• Best Suitable for Out of Position Welding• Suitable for Welding Thin Sheets• Relatively Large opening of Root Can be Welded• Less Distortion• Best Suitable for Tacking in Set up • Prone to Get Lack of Fusion in Between Beads
PRESENTATION BY: HARDISH TRIVEDI
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Globular Transfer
• Metal transferred in droplets of Size grater than wire diameter
• Operates in Moderate Amps & Volts – Better Deposition
• Common in Co2 Flux Cored and Solid Wire
• Suitable for General purpose Welding
PRESENTATION BY: HARDISH TRIVEDI
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Free Flight / Spray Transfer• Metal transferred in multiples of small droplets• 100 to 1000 Droplets per Second• Metal Spray Axially Directed• Electrode Tip Remains pointed• Applicable Only With Inert Gas Shielding
– Not With Co2
• Operates in Higher Amps & Volts – Higher Deposition Rate
• Not Suitable for Welding in Out of Position.• Suitable for Welding Deep Grooves
PRESENTATION BY: HARDISH TRIVEDI
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Pulsed Spray Welding
• Power Source Provides Two different Current Levels“Background” and “Peak”at regular interval
• “Background” & “Peak” are above and below the Average Current
• Best Suitable for Full Penetration Open Root Pass Welding
• Good Control on Bead Shape and Finish
PRESENTATION BY: HARDISH TRIVEDI
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Synergic Pulse GMAW
• Parameters of Pulsed Current (Frequency, Amplitude, Duration, Background Current) Related to Wire feed Rate
• One Droplet detaches with each pulse• An Electronic Control unit synchronizes wire feed
Rate with Pulse Parameters • Best Suitable for Most Critical Full Penetration
Open Root Pass Welding• Good Control on Open Root penetration, Bead
Shape and Finish
PRESENTATION BY: HARDISH TRIVEDI
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GMAW Process Variables• Current• Voltage• Travel Speed• Stick Out / Electrode Extension • Electrode Inclination • Electrode Size• Shielding Gas & Flow Rate• Welding Position
PRESENTATION BY: HARDISH TRIVEDI
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Parameter For 1.2 ф FC Wire• Current – 200 to 240 A
• Voltage – 22-24
• Travel Speed 150 to 250 mm / min
• Stick Out / Electrode Extension – 15 to 20 mm
• Electrode Inclination – Back Hand Technique
• Shielding Gas – Co2, 12 L/Min
PRESENTATION BY: HARDISH TRIVEDI
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Parameter For 1.2 ф Solid Wire• Current – 180 to 220 A
• Voltage – 20-22
• Travel Speed 150 to 200 mm / min
• Stick Out / Electrode Extension – 10 to 20 mm
• Electrode Inclination – Back Hand Technique
• Shielding Gas – Co2 – 12 L/Min
PRESENTATION BY: HARDISH TRIVEDI
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Results In Change Of Parameters• Increase In Current
– More deposition, More Penetration, More BM Fusion• Increase In Voltage
– More Weld Bead Width, Less Penetration, Less Reinforcement, Excess Spatter
• Increase In Travel Speed– Decrease in Penetration, Decrease in Bead Width,
• Decrease In Gas Flow rate– Results In porosity
• Long Stick Out / Electrode Extension– Excess Weld Deposit With Less Arc intensity, Poor Bead Finish,
Shallow Penetration
PRESENTATION BY: HARDISH TRIVEDI
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Common Defects In GMAW
1. Porosity 2. Spatters
3. Lack Of Fusion 4. Under Cut
5. Over Lap 6. Slag
7. Crack 8. Lack Of Penetration
9. Burn Through 10. Convex Bead
11. Unstable Arc 12. Wire Stubbing
PRESENTATION BY: HARDISH TRIVEDI
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Porosity
Cause Remedy1) Less Mn & Si In Wire
2) Rusted / Unclean BM / Groove
3) Rusted wire
4) Inadequate Shielding Gas
1) Use High Mn & Si Wire
2) Clean & warm the BM
3) Replace the Wire
4) Check & Correct Flow Rate
Porosity . .
PRESENTATION BY: HARDISH TRIVEDI
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SpattersCause Remedy
1) Low Voltage
2) Inadequate Inductance
3) Rusted BM surface
4) Rusted Core wire
5) Quality Of Gas
1) Increase Voltage
2) Increase Inductance
3) Clean BM surface
4) Replace By Rust Free wire
5) Change Over To Ar + Co2
Spatters• • •
PRESENTATION BY: HARDISH TRIVEDI
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Lack Of FusionCause Remedy
1) Inadequate Current
2) Inadequate Voltage
3) Wrong Polarity
4) Slow Travel Speed
5) Excessive Oxide On Joint
1) Use Right Current
2) Use Right Voltage
3) Connect Ele. + Ve
4) Increase Travel speed
5) Clean Weld Joint
Lack Of Fusion
PRESENTATION BY: HARDISH TRIVEDI
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Undercut
Cause Remedy
1) Excess Voltage
2) Excess Current
3) Improper Torch angle
4) Excess Travel Speed
1) Reduce Voltage
2) Reduce Current
3) Train & Qualify the Welder
4) Reduce Travel Speed
Under cut
PRESENTATION BY: HARDISH TRIVEDI
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Overlap
Cause Remedy
1) Too Long Stick Out
2) Inadequate Voltage
1) Reduce Stick Out
2) Increase the Voltage
Overlap
PRESENTATION BY: HARDISH TRIVEDI
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SlagCause Remedy
1) Inadequate Cleaning
2) Inadequate Current
3) Wrong Torch angle
4) Improper bead placement
1) Clean each bead
2) Use Right Current
3) Train / Qualify welder
4) Train / Qualify Welder
Slag
PRESENTATION BY: HARDISH TRIVEDI
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Crack
Cause Remedy
1) Incorrect Wire Chemistry 2) Too Small Weld Bead
3) Improper Preheat
4) Excessive Restrain
1) Use Right Wire
2) Increase wire Feed
3) Preheat Uniformly
4) Post heating or ISR
crack
PRESENTATION BY: HARDISH TRIVEDI
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Lack Of Penetration*Cause Remedy
1) Too Narrow Groove Angle
2) Inadequate Root opening
3) Too Low Welding current
4) Wrong Torch angle
5) Puddle Roll In Front Of Arc
6) Long Stick Out
1) Widen The Groove
2) Increase Root Opening
3) Increase Current
4) Train / Qualify Welder
5) Correct Torch Angle
6) Reduce Stick Out
LOP
* Applicable to SSFPW
PRESENTATION BY: HARDISH TRIVEDI
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Burn through*Cause Remedy
1) Excess Current
2) Excess Root opening
3) Inadequate Root face
4) Too Low Travel Speed
5) Quality Of Gas
1) Reduce the Current
2) Reduce root opening
3) Increase root face
4) Increase Speed
5) Use Ar + Co2
Burn trough*Applicable to root pass
PRESENTATION BY: HARDISH TRIVEDI
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Convex Bead FinishCause Remedy
1) Low Current
2) Low Voltage
3) Low Travel Speed
4) Low Inductance
5) Too Narrow Groove
1) Increase Current
2) Increase Voltage
3) Increase Travel Speed
4) Increase Inductance
5) Increase Groove Width
Uneven bead finish
PRESENTATION BY: HARDISH TRIVEDI
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Unstable arc
Cause Remedy
1) Improper Wire Feed
2) Improper Gas Flow
3) Twisted Torch Conduit
1) Check Wire Feeder
2) Check Flow Meter
3) Straighten Torch Cab
PRESENTATION BY: HARDISH TRIVEDI
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Wire Stubbing
Cause Remedy
1) Too Low Voltage
2) Too High Inductance
3) Excess Slope
4) Too Long Stick Out
1) Increase Voltage
2) Reduce Inductance
3) Adjust Slope
4) Reduce Stick Out
PRESENTATION BY: HARDISH TRIVEDI
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Important Terminology used in Critical Welding
• Preheating
• Post Heating or Dehydrogenation
• Intermediate Stress leaving
• Inter pass Temperature
• Post Weld Heat Treatment
PRESENTATION BY: HARDISH TRIVEDI
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What Is Preheating?
• Heating the base metal along the weld joint to a predetermined minimum temperature immediately before starting the weld.
• Heating by Oxy fuel flame or electric resistant coil• Heating from opposite side of welding wherever
possible• Temperature to be verified by thermo chalks prior to
starting the weld
PRESENTATION BY: HARDISH TRIVEDI
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Why Preheating?
• Preheating eliminates possible cracking of weld and HAZ• Applicable to
Hardenable low alloy steels of all thickness
Carbon steels of thickness above 25 mm.
Restrained welds of all thickness
• Preheating temperature vary from 75°C to 200°C depending on hardenability of material, thickness & joint restrain
PRESENTATION BY: HARDISH TRIVEDI
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How does Preheating Eliminate Crack?
• Preheating promotes slow cooling of weld and HAZ
• Slow cooling softens or prevents hardening of weld and HAZ
• Soft material not prone to crack even in restrained condition
PRESENTATION BY: HARDISH TRIVEDI
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What Is Post Heating?
• Raising the pre heating temperature of the weld joint to a predetermined temperature range (250° C to 350° C) for a minimum period of time (3 Hrs) before the weld cools down to room temperature.
• Post heating performed when welding is completed or terminated any time in between.
• Heating by Oxy fuel flame or electric resistant coil• Heating from opposite side of welding wherever possible• Temperature verified by thermo chalks during the period
PRESENTATION BY: HARDISH TRIVEDI
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Why Post Heating?
• Post heating eliminates possible delayed cracking of weld and HAZ
• Applicable to
Thicker hardenable low alloy steels
Restrained hardenable welds of all thickness• Post heating temperature and duration depends on
hardenability of material, thickness & joint restrain
PRESENTATION BY: HARDISH TRIVEDI
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How does Post Heating Eliminate Crack?
• SMAW introduces hydrogen in weld metal• Entrapped hydrogen in weld metal induces
delayed cracks unless removed before cooling to room temperature
• Retaining the weld at a higher temperature for a longer duration allows the hydrogen to come out of weld
PRESENTATION BY: HARDISH TRIVEDI
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What Is Intermediate Stress Relieving? • Heat treating a subassembly in a furnace to a
predetermined cycle immediately on completion of critical restrained weld joint / joints without allowing the welds to go down the pre heat temperature. Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thickness
• Applicable to
Highly restrained air hardenable material
PRESENTATION BY: HARDISH TRIVEDI
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Why Intermediate Stress Relieving?
• Restrained welds in air hardenable steel highly prone to crack on cooling to room temperature.
• Cracks due to entrapped hydrogen and built in stress
• Intermediate stress relieving relieves built in stresses and entrapped hydrogen making the joint free from crack prone
PRESENTATION BY: HARDISH TRIVEDI
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What Is Inter- Pass Temperature?
• The temperature of a previously layed weld bead immediately before depositing the next bead over it
• Temperature to be verified by thermo chalk prior to starting next bead
• Applicable to
Stainless Steel
Carbon Steel & LAS with minimum impact
PRESENTATION BY: HARDISH TRIVEDI
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Why Inter Pass Temperature?
• Control on inter pass temperature avoids over heating, there by
Refines the weld metal with fine grains
Improves the notch toughness properties
Minimize the loss of alloying elements in welds
Reduces the distortion
PRESENTATION BY: HARDISH TRIVEDI
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What Is Post Weld Heat Treatment?
• Heat treating an assembly on completion of all applicable welding, in an enclosed furnace with controlled heating/cooling rate and soaking at a specific temperature for a specific time.
• Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thickness
• Applicable to
All type of CS & LAS
PRESENTATION BY: HARDISH TRIVEDI
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Why Post Weld Heat Treatment?
• Welded joints retain internal stresses within the structure
• HAZ of welds remains invariably hardened
• Post Weld Heat Treatment relieves internal stresses and softens HAZ. This reduces the cracking tendency of the equipment in service
PRESENTATION BY: HARDISH TRIVEDI
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Thanks