gtaw (tig). definition gas tungsten arc welding (gtaw) is an arc welding process that uses a non...

GTAW(TIG)

Definition

Gas Tungsten Arc Welding (GTAW) is an arc welding process that uses a non consumable tungsten electrode to establish the arc and gas from a cylinder to provide shielding. The filler metal is supplied by a manual rod.

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Also called Tungsten Inert Gas (TIG) welding.

Machine Functions

1 Store and provide shielding gas at the correct rate

2 Provide desired welding current

3 Variable current control

4 Store and circulate water through the torch (watered cooled)

5 Semiautomatic control

Machine Nomenclature

A. TorchB. Power switchC. AC balance controlD. Mode switchE. Digital Amp meterF. Output (Amp) controlG. CylinderH. Flow meterI. Roto meterJ. Flow control valveK. RegulatorL. Post flow timerM. Pulse frequency controlN. Polarity switchO. Output connectorP. Remote pedalQ. Ground clampR. Remote receptacle Explain the function(s) of each one of these

controls/parts.

Torch Nomenclature

A. Cap

B. Collet

C. Torch body

D. Collet body

E. Gas orifice

F. Cup

G. Electrode

What is the function of each part?

How are GTAW torches cooled?

Introduction

Heat Shielding Filler metal

GTAW

How does the GTAW process meet the three requirements of arc welding?

Hazards Associated with GTAW

Hot metal

Harmful rays

Fumes

High frequency RF

Flying objects

Loud Noise

What is the best management practices for these hazards?

Heat

The heat produced by an electric arc between the nonconsumable tungsten and the metal is sufficient to melt the base metal and the filler rod.

What determines the amount of heat produced by the electric arc?

For the TIG welding process, is the current adjusted by changing the amperage or the voltage?

Heat – Currents

Three common currents:

DC-

DC+

AC--HF

Note: many power supplies have the option of pulsed current for better puddle control.

Why is HF (high frequency) used with AC?

Heat – Current - Polarity

For the best welds, and ease of welding, the correct current must be used for the metal being welded.

Heat - Tungsten

The tungsten electrode is nonconsumable and is used to form the arc between the torch and the metal.Different alloys of tungsten are available.

EWP 100 % Tungsten Green

EWTh-2 2 % Thorium Red

EWZr-1 1 % Zirconium Brown

EWCe-2 2 % Cerium Orange

EWLa-2 2 % Lanthanum Black

Good arc stability with AC

Better Arc with DC

AC when high weld quality is required

Better starting, higher current

50% greater current capacity with AC

ID % Alloy Color Characteristic

Which alloy/color should be used when welding thicker aluminum with AC?

Heat – Tungsten - Preparation

The shape of the tungsten electrode end must be appropriate for the current being used.

AC Hemispheric or balled end no more than 1.5 times the electrode diameter. Grinder lines parallel with electrode.

DC- Needle point for very thin metal, blunt point for thicker metal. Taper = 2 to 2-1/2 times the diameter.

What does it mean if the end of the electrode appears dull?

What does it mean if the end of the electrode is blue or blackened?

How long should the the shielding gas flow after the welding has stopped?

Heat – Tungsten - Size

Diameter(in)

Gas Cup Inside Dia.

DC-(Ce, Th % La)

AC (Pure)

AC(Ce, Th % La)

0.040 #5 (3/8 in) 15 – 80 20 – 60 15 - 80

0.060 (1/16 in) #5 (3/8 in) 70 - 150 50 – 100 70 – 150

0.093 (3/16 in) #8 (1/2 in) 150 – 250 100 - 160 140 – 235

0.125 (1/8 in) #8 (1/2 in) 250 – 400 150 – 200 225 - 325

Shielding

In the GTAW process shielding is supplied from a cylinder.

For best results the shielding gas must be appropriate for the type and thickness of metal.

How is the flow of the shielding gas controlled?

How much gas (ft3) will each gallon of liquid argon produce?

Filler Metal

A welding rod is used to fill in the joint.

Most common type is 36 inch rods that are fed into the weld pool by hand.

What are three important characteristics of GTAW rods?

AWS GTAW Aluminum Filler Rods

1100 ER1100

2014-T6

2219-T81

3003

5005

Aluminum Alloy

ER4043

ER2319

ER1100

ER5356

Filler Rod

Process

Preparation for Welding

Three (3) steps in preparing to weld:

1 Safety check

2 Metal preparation

3 Set up machine

Preparation - Safety

1 Check the machine, cables, torch and ground clamp.

2 Insure the helmet is in good condition and the correct shade of lens.

3 Cover all exposed skin.

Preparation – Metal – Aluminum

• Contamination is the biggest problem when welding aluminum with the GTAW process.

• The metal must be cleaned with a stainless steel wire brush.

The brush can only be used to clean aluminum. Must clean the adjoining faces and the back edge

• Insure the filler rod is clean also.

Preparation - Machine

• Attach the GTAW torch to the output connector.• Attach the remote control pedal to the remote

receptacle.• Position the polarity switch on AC.• Turn on the machine.

Insure the torch is not grounded

• Set the mode switch to TIG• Set the amperage.

150 amp maximum for air cooled torch.

• Set the AC balance control.• Set the pulse control.• Set the postflow timer.

Preparation – Machine - Torch

• If the torch has been used to weld carbon steel or stainless steel then the cup and electrode must be replaced.

• The tungsten electrode must be clean and the correct shape.

• The torch cup must be clean• The electrode must be set with the correct

stickout.

Welding aluminum

Setting Amperage

Aluminum is a good conductor of heat.

Aluminum melts at a lower temperature that steel.Aluminum Amperage ACHF

Thickness Joint

Tungsten electrode diameter

Filler rod diameter Amperage

Gas

Type CFH

1/8 in

Butt 3/32 – 1/8 in 3/32 in 125 - 150 Argon 20

Lap 3/32 – 1/8 in 3/32 in 130 - 160 Argon 20

Corner 3/32 – 1/8 in 3/32 in 120 - 140 Argon 20

Fillet 3/32 – 1/8 in 3/32 in 130 - 160 Argon 20

3/16 inButt 1/8 – 5/32 in 1/8 in 180 - 225 Argon 20

Lap 1/8 – 5/32 in 1/8 in 190 - 240 Argon 20

Corner 1/8 – 5/32 in 1/8 in 180 - 225 Argon 20

Fillet 1/8 – 5/32 in 1/8 in 190 – 240 Argon 20

1/4 inButt 5/32 – 3/16 in 3/16 in 240 - 280 Argon 25

Lap 5/32 – 3/16 in 3/16 in 250 – 320 Argon 25

Corner 5/32 – 3/16 in 3/16 in 240 - 280 Argon 25

Fillet 5/32 – 3/16 in 3/16 in 250 - 320 Argon 25

Troubleshooting GTAW

• Troubleshooting is the process of determining the cause of a problem.

• Assumes the welder is in proper working order.• Requires gathering information and a logical

thought process.

Troubleshooting - 1

Problem Cause

Excessive electrode consumption Inadequate gas flow

DCEP electrode

Excessive current density

Tungsten oxidation during cooling

What would you do to remedy these causes?

Troubleshooting - 2

Problem Cause

Aluminum contamination of electrode Electrode contacting filler rod

Electrode contacting metal

What would you do to remedy these causes?

Troubleshooting - 3

Problem Cause

Weld porosity and dark color Condensation in system

Atmospheric contamination

Contaminated filler metal

Contaminated base metal

What should be done to remedy these causes?

Troubleshooting - 4

Problem Cause

Yellow powder or smoke on cup Insufficient gas flow

Atmospheric contamination

Inadequate post flow

Incorrect shielding gas

What should be done to remedy these causes?

Incorrect tungsten size or cup size

References

http://www.millerwelds.com/resources/TIGhandbook/