Gas Tungsten Arc Welding

Gas Tungsten Arc Welding

By HARDISH TRIVEDI

1PRESENT BY:HARDISH TRIVEDI

GTAW

• Fusion Welding Process

• Arc Between Non-Consumable Tungsten Rod And Work

• Arc & Weld Pool Shielded By Argon

• Filler Wire Separately Added To Weld Pool

• Welding Torch & Tungsten Rod Cooled by Flow OF Argon / Cooling Water


Shielding Gas• Inert Gas - Argon , Helium• Common Shielding Gas – Argon• When Helium Is Used – Called “Heli – Arc” Welding• When Argon Is Used – Called “Argon Arc” Welding• Inert Gas Prevents Contamination Of Molten Metal• It Prevents Oxidation Of Tungsten Rod• It Ionizes Air Gap and Stabilizes Arc• It Cools Welding Torch & Tungsten Rod


Equipment & Accessories

– +

Argon Gas In

Flow Meter

Welding Cable & Cooling Water In Tube

HF Unit & Water Cooling

System

Argon Cylinder

Pressure Regulator

Cooling Water In

Cooling Water OutArgon Shielding

Tungsten Rod

Power Source

Work

Arc

+High Frequency

Connection

Solenoid Valve

Ceramic Cup

Pedal Switch

Gas Lens

Collet


GTAW Equipment & Accessories

• Power Source – Inverter, Thyrester,Rectifier, Generator

• High Frequency Unit• Water Cooling System• Welding Torch- (Ceramic Cup, Tungsten Rod,

Collet, Gas-lens) • Pedal Switch• Argon Gas Cylinder • Pressure Gauge, Regulator, Flow Meter • Earthing Cable With Clamp


Types Of GTAW Power Source

• Inverter- DC

• Thyrester – DC

• Motor Generator – DC

• Rectifier – DC

• Transformer – AC (For Aluminium Welding Only)


Power Source

• Provides Electric Energy – Arc – Heat

• Drooping Characteristic

• OCV – Appx. 80V,

• Current Range 40 A to 300 A ( Capacity Of M/s)

• Arc Voltage 18V to 26V


Characteristic Of GTAW Power Source

A

Vertical Curve

V1

V2

A1 A2

Drooping – Constant Current

V


High Frequency Unit

• Provides High Voltage Electric Energy With Very high Frequency – 10000 Cycles / Sec.

• Initiates low energy Arc / Spark & Ionize Air Gap.

• Electrically charges Air Gap For welding Current to Jump Across the Tungsten Tip & BM to Form An Arc.

• HF Gets Cut Off, Once Welding Arc Struck.9PRESENT BY:HARDISH TRIVEDI

Water Cooling System

• Provides Cooling Water To Welding Torch.

• Cools Tungsten Rod, Torch handle & Welding Cable.

• Cooling Water Returns through Flexible Tube Which Carries welding cable within.


Pedal Switch

Sequence

When M/c On• Power source gets energized• Pump starts pumping cooling water to torch When Pedal Switch Pressed with tungsten rod held close to BM within 3mm• Solenoid valve opens, Argon starts flowing • After 5 seconds of pre-purging, high Frequency current jumps from tungsten

rod generating sparks • Immediately welding current makes arc across tungsten rod and work

through the HF sparks. • High frequency gets cut off from the system when welding arc is initiated and

welding is started. When Pedal Released without lifting the torch1 Current gets cut off, Arc extinguishes, Gas flow continues as post purging.2 Gas flow remains for few more seconds before it stops.3 Torch to be lifted only after post purging stops


Argon Gas Cylinder- Pressure Regulator + Flow Meter

• Cylinder Stores Argon At High Pressure

• Regulator Regulates Cylinder Pressure to Working Pressure

• Flow Meter Controls Flow Rate

Argon Cylinder

Flow Meter

Pressure Regulator

Flow Regulator

Pressure gauges

Cylinder Valve

Connection To Torch


Shielding Gas• Argon - Purity 99.99%

• Impure Argon Results In Porosities

• Purity Verified by Fusing BQ CS plate

• Leakage of Argon in Torch Results in Porosity.

• Check Leakage by Closing the Ceramic Cup With Thumb


Argon Gas Cylinder• Light Blue In Colour

• Full Cylinder Pressure: 1800 psi ( 135 Kgs / Cm2 )

• Volume Of Argon In Full Cylinder: 7.3 M3

• Commercial Argon (99.99%) Cost: Rs 90/- Per M3

• High Purity Argon (99.999) Cost: Rs 110/- Per M3


Back Purging

Purging Gas Commercial Argon or Nitrogen

• Applicable to Single Sided full penetration

• Prevents oxidation of root pass from opposite side of weld

• Essential for high alloy steels, nonferrous metals and alloys

• Desirable For All Material

Welding Torch

Root Pass

Purging Gas InPurging Gas Out

Purging chamber

Filler Wire


Tools For GTAW

• Head Screen

• Hand gloves

• Chipping Hammer

• Wire Brush

• Spanner Set


Tungsten Rod

• Non Consumable Electrode.

• Maintains Stable Arc

• Tip to be Ground to a cone Shape of 60º to 30º angle

• Thoriated Tungsten for General Application, Zerconiated Tungsten for Aluminium Welding

• Sizes :- 2, 2.4 & 3 mm Ø

Tungsten Rod

Ground to 50º ankle


Pulsed GTAW

• 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

• Ideal for Root Pass by Automatic Machine Welding


Filler Wire

• Added Separately to the weld pool.

• Compatible to base metal

• Used in cut length for manual welding.

• Used from layer wound spool for automatic welding.

• Sizes :- 0.8, 1, 1.2, 1.6, 2, 2.4 & 3 mm


ASME Classification Of Filler Wire

SS Filler Wire:

SFA-5.9, ER 308, 308L, 316, 316L, 347, 309

LAS Filler Wire:

SFA 5.28, ER 70S A1, ER 80S B2, ER90S D2,

ER 80S Ni2

CS Filler Wire:

SFA- 5.18 , ER 70S2 C = 0.07%, Mn = 0.9% – 1.4%, Si = 0.4 – 0.7%, P = 0.025%, S = 0.035%


Dos & Don'ts In GTAW

• Always Connect Electrode – Ve

• Keep Always Flow Meter Vertical

• Check & Confirm Argon Purity

• Clean Groove & Filler wire With Acetone

• Grind Tungsten Tip to Point

• Don’t Strike Arc With Electrode + Ve

• Don’t strike Arc Without Argon Flow

• Don’t Strike Arc By touching Tungsten Rod

• Don’t Touch Weld Pool With Tungsten Rod

• Don’t Lift and break Arc

Dos Don’ts



• Break The Arc Only By Pedal Switch

• Lift The Torch only After 5 Sec Of Arc Break.

• Ensure Pre Purging & Post Purging of 5Sec

• Ensure Argon Flow & Water Circulation To Torch

• When Arc is Stopped Don’t Lift Torch immediately.

• Don’t Weld With Blunt Tungsten Rod

• Don’t Weld With Argon Leaking Torch

• Don’t Weld Without Water Circulation

Dos Don’ts



• Provide Back Purging For Single Sided Full Penetration Welds

• Use N2 or Argon as Back Purging Gas For CS & LAS

• Use Argon As Back Purging Gas For SS & Non Ferrous Alloys

• Don’t Weld Single Sided Full Penetration Welds Without Back Purging

• Don’t Use N2 As Back Purging Gas For Non Ferrous Alloys

• Don’t Empty Ag Cylinders Fully.

Dos Don’ts


Defects In GTAW

1. Cracks 2. Lack Of Fusion

3. Porosity 4. Undercut

5.Lack Of Penetration 6. Excess Penetration

7.Overlap 8. Suck Back

9. Under Flush 10. Burn Through

11. Tungsten Inclusion 11.Stray Arcing


Crack

Cause Remedy

1) Wrong Consumable

2) Wrong Procedure

3) Improper Preheat

4) Inadequate Thickness In Root Pass

1) Use Right Filler Wire

2) Qualify Procedure

3) Preheat Uniformly

4) Add More Filler Wire in root Pass

crack


Lack Of Fusion

Cause Remedy

1) Inadequate Current

2) Wrong Torch angle

3) Improper bead placement

1) Use Right Current

2) Train /Qualify welder

3) Train/Qualify Welder

Lack Of Fusion


PorosityCause Remedy

1) Impure Argon Gas

2) Argon Leak Within Torch

3) Defective Filler Wire

4) Wet surface of BM

5) Rusted / Pitted Filler wire

6) Improper Flow Of Argon

1) Replace Argon Cylinder

2) Replace Leaking Torch

3) Replace Filler Wire

4) Clean & Warm BM

5) Clean Filler Wire

6) Provide Gas lens

Porosity . .


Undercut

Cause Remedy

1) Excess Current

2) Excess Voltage

3) Improper Torch angle

1) Reduce the Current

2) Reduce Arc length

3) Train & Qualify the Welder

Under cut


Lack Of Penetration*Cause Remedy

1) Excess Root Face

2) Inadequate Root opening

3) Over size Filler Wire

4) Wrong Direction of Arc

5) Improper bead placement

6) Improper weaving technique

1) Reduce Root Face

2) Increase Root Opening

3) Reduce Filler Wire size

4) Train / Qualify Welder


6) Train & Qualify Welder

LOP

* Applicable to SSFPW


Excess Penetration*Cause Remedy

1)Excess root opening

2) Excess Current

3) Inadequate root face

4) Excess Weaving

5) Wrong Direction Of Arc

1) Reduce root gap

2) Reduce Current

3) Increase Root face

4) Train Welder

5) Train Welder

Excess Penetration

* Applicable to SSFPW


Overlap

Cause Remedy

1) Wrong Direction Of Arc

2) Inadequate Current

3) Excess Filler Wire

1) Train & Qualify Welder

2) Increase Current

3) Reduce Filler Metal

Overlap


Suck Back*Cause Remedy

1) Excess weaving in root

2) Excess Current

3) Inadequate root face

4) Wrong Electrode angle

1) Reduce weaving

2) Reduce Current

3) Increase root face


Suck Back

* Applicable to SSFPW in 4G, 3G & 2G


Under flushCause Remedy

1) Inadequate weld beads in

final layer

2) Inadequate understanding on

weld reinforcement

3) Wrong selection of filler wire

size

1) Weld some more beads

in final layer

2) Train / Qualify welder


Under flush


Burn through*Cause Remedy

1) Excess Current

2) Excess Root opening

3) Inadequate Root face

4) Improper weaving

1) Reduce the Current

2) Reduce root opening

3) Increase root face


Burn trough

*Applicable to root pass


Tungsten InclusionCause Remedy

1) Ineffective HF

2) Improper Starting of Arc

3) Tungsten Tip Comes in

Contact With Weld

1) Rectify HF Unit

2) Never Touch Weld

With Tungsten Rod

3) Train / Qualify welder

Tungsten Inclusion


Stray Arcing

Cause Remedy

1) HF Not In Operation

2) Inadequate Skill of Welder

1) Rectify HF Unit

2) Train the Welder

Arc Strikes


Thanks


Documents

Gas Tungsten Arc Welding