Gas Tungsten Arc Welding

By L D Poyyara

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

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. 90V, • 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.

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.

GTAW TORCH

Tungsten Rod

Ceramic Cup

Arc

Argon Gas Inlet

Cooling Water Outlet

Cooling Water Inlet Tube with cable

Base Metal

Torch HandleCap with collet For Holding Tungsten

Argon Shielding Gas

Earthing Cable

Pedal Switch

Switches system on And off in

sequence

When Pedal Pressed• Solenoid valve opens, Argon gas

flows• High Frequency current jumps from

tungsten rod generating sparks• Welding current flows generating an

arc across tungsten rod and work. • High frequency gets cut off from the

system & welding continues. When Pedal Released1 Current gets cut off, Arc extinguishes 2 Gas flow remains for few more

seconds before it 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 gaugesCylinder Valve

Connection To Torch

Shielding Gas• Argon - Purity 99.95%

• 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 Thump

Argon Gas Cylinder• Light Blue In Colour

• Full Cylinder Pressure: 1800 psi ( 130 Kgs / Cm2 )

• Volume Of Argon In Full Cylinder: 7.3 M3

• Commercial Argon (99.99%) Cost: Rs 70/- Per M3

• High Purity Argon (99.999) Cost: Rs 87/- 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

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

Dos & Don'ts In GTAW

• 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 Blend Tungsten Rod

• Don’t Weld With Argon Leaking Torch

• Don’t Weld Without Water Circulation

Dos Don’ts

Dos & Don'ts In GTAW

• 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 Remedy1) Wrong Consumable2) Wrong Procedure3) Improper Preheat4) Inadequate Thickness

In Root Pass

1) Use Right Filler Wire2) Qualify Procedure3) Preheat Uniformly4) Add More Filler Wire

in root Pass

crack

Lack Of Fusion

Cause Remedy1) Inadequate Current2) Wrong Torch angle3) Improper bead placement

1) Use Right Current2) Train /Qualify welder3) Train/Qualify Welder

Lack Of Fusion

PorosityCause Remedy

1) Impure Argon Gas2) Argon Leak Within Torch3) Defective Filler Wire4) Wet surface of BM5) Rusted / Pitted Filler wire6) Improper Flow Of Argon

1) Replace Argon Cylinder2) Replace Leaking Torch 3) Replace Filler Wire4) Clean & Warm BM5) Clean Filler Wire6) Provide Gas lens

Porosity . .

Undercut

Cause Remedy1) Excess Current2) Excess Voltage3) Improper Torch angle

1) Reduce the Current2) Reduce Arc length3) Train & Qualify the Welder

Under cut

Lack Of Penetration*Cause Remedy

1) Excess Root Face2) Inadequate Root opening3) Over size Filler Wire4) Wrong Direction of Arc5) Improper bead placement6) Improper weaving technique

1) Reduce Root Face2) Increase Root Opening3) Reduce Filler Wire size4) Train / Qualify Welder5) Train / Qualify Welder6) Train & Qualify Welder

LOP

* Applicable to SSFPW

Excess Penetration*Cause Remedy

1)Excess root opening2) Excess Current3) Inadequate root face 4) Excess Weaving 5) Wrong Direction Of Arc

1) Reduce root gap2) Reduce Current3) Increase Root face4) Train Welder5) Train Welder

Excess Penetration

* Applicable to SSFPW

Overlap

Cause Remedy1) Wrong Direction Of Arc2) Inadequate Current3) Excess Filler Wire

1) Train & Qualify Welder2) Increase Current3) Reduce Filler Metal

Overlap

Suck Back*Cause Remedy

1) Excess weaving in root2) Excess Current3) Inadequate root face 4) Wrong Electrode angle

1) Reduce weaving2) Reduce Current3) Increase root face4) Train / Qualify Welder

Suck Back

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

Under flushCause Remedy

1) Inadequate weld beads in final layer2) Inadequate understanding on weld reinforcement 3) Wrong selection of filler wire size

1) Weld some more beads in final layer2) Train / Qualify welder

3) Train / Qualify Welder

Under flush

Burn through*Cause Remedy

1) Excess Current2) Excess Root opening3) Inadequate Root face4) Improper weaving

1) Reduce the Current2) Reduce root opening3) Increase root face4) Train / Qualify Welder

Burn trough

*Applicable to root pass

Tungsten InclusionCause Remedy

1) Ineffective HF2) Improper Starting of Arc

3) Tungsten Tip Comes in Contact With Weld

1) Rectify HF Unit2) Never Touch Weld With Tungsten Rod3) Train / Qualify welder

Tungsten Inclusion

Stray Arcing

Cause Remedy1) HF Not In Operation2) Inadequate Skill of Welder

1) Rectify HF Unit2) Train the Welder

Arc Strikes

Thanks