1. Chapter 15
Gas Tungsten Arc Welding Equipment, Setup, Operation, and Filler Metals

2. Objectives
Describe the gas tungsten arc welding process and list the other terms used to describe it
Explain what makes tungsten a good electrode
Tell how tungsten erosion can be limited
Discuss how the various types of tungsten electrodes are used
Tell how to shape the end of the tungsten electrode and how to clean it

3. Objectives (cont'd.)
Demonstrate how to grind a point on a tungsten electrode using an electric grinder
Demonstrate how to remove a contaminated tungsten end
Demonstrate how to melt the end of the tungsten electrode into the desired shape
Compare water-cooled GTA welding torches to air-cooled torches

4. Objectives (cont'd.)
Tell the purposes of the three hoses connecting a water-cooled torch to the welding machine
Discuss how to choose an appropriate nozzle for the job
Tell what procedures must be followed to get an accurate reading on a flowmeter
Compare the three types of welding current used for GTA welding

5. Objectives (cont'd.)
Discuss the shielding gases used in the GTA welding process
Define preflow and postflow
Explain the problems that can occur as a result of an incorrect gas flow rate
Demonstrate how to properly set up a GTA welder
Demonstrate how to establish a GTA welding arc

6. Introduction Gas tungsten arc welding (GTAW) process
Sometimes referred to as a TIG or heliarc
TIG: short for tungsten inert gas
Arc is established between a nonconsumable tungsten electrode and base metal
Inert gas provides needed arc characteristics and protects the molten weld pool
Became more common when Argon became plentiful

7. Tungsten
Properties
High tensile strength
Hardness
High melting temperature
High boiling temperature
Good electrical conductivity
Produced mainly by reduction of its trioxide with hydrogen

8. Tungsten (cont'd.) Best choice for a nonconsumable electrode
High melting temperature
Good electrical conductivity
Electrode becomes hot
Arc between electrode and work stabilizes
Because of the intense heat, some erosion of the electrode will occur

9. FIGURE 15-1 Some tungsten will erode from the electrode, be transferred across the arc, and become trapped in the weld deposit.
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10. Tungsten (cont'd.) Several ways to limit erosion
Good mechanical and electrical contact
Use as low a current as possible
Use a water-cooled torch
Use as large as a tungsten electrode as possible
Use DCEN current
Use as short as an electrode extension as possible
Use the proper shape electrode
Use an alloyed tungsten electrode

11. Tungsten (cont'd.) Collet Large-diameter electrodes
Cone-shaped sleeve
Holds electrode in the torch
Large-diameter electrodes
Conduct more current
Current-carrying capacity at DCEN
About ten times greater than at DCEP
Preferred electrode tip shape
Impacts temperature and erosion of tungsten

12. FIGURE 15-2 Irregular surface of a cleaned tungsten electrode (poor heat transfer to collet).
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13. Types of Tungsten Electrodes
Pure tungsten
Excellent nonconsumable electrode
Can be improved by adding:
Cerium
Lanthanum
Thorium
Zirconium

14. Types of Tungsten Electrodes (cont'd.)
Classifications
Pure Tungsten, EWP
1% thorium tungsten, EWTh-1
2% thorium tungsten, EWTh-2
¼% to ½% zirconium tungsten, EWZr
2% cerium tungsten, EWCe-2
1% lanthanum tungsten, EWLa-1
Alloy not specified, EWG

15. Table 15-1 Tungsten Electrode Types and Identification.

16. Shaping the Tungsten Methods to obtain desired end shape Grinding
Breaking
Remelting the end
Using chemical compound

17. Grinding
Often used to clean a contaminated tungsten or to point the end
Should have a fine, hard stone
Coarse grinding stone with result in more tungsten breakage
Should be used for grinding tungsten only
Metal particles will quickly break free when the arc is started, causing contamination

18. FIGURE 15-8 Correct way of holding a tungsten when grinding.
Larry Jeffus

19. Breaking and Remelting
Tungsten is hard but brittle
Struck sharply: will break without bending
Holding against a sharp corner and hitting
Results in a square break
After breaking squarely: melt back the end

20. Chemical Cleaning and Pointing
Tungsten
Can be cleaned and pointed using one of several compounds
Heated by shorting it against the work
Dipped in the compound
Removed, cooled, and cleaned
End will be tapered to a fine point
Contaminated electrode
Chemical compound will dissolve the tungsten and allow contamination to fall free

21. Pointing and Remelting
Tapered tungsten with a balled end
Made by first grinding or chemically pointing the electrode
Ball should be made large enough so color of the end stays dull red and bright red
Increase ball size by applying more current
Surface tension pulls molten tungsten up onto the tapered end

22. GTA Welding Equipment Torches Water-cooled: more efficient
Air-cooled: more portable
Hoses
Water-cooled: three hoses connect it
Air-cooled: may have one hose for shielding gas
Nozzle
Directs shielding gas directly on welding zone
Flowmeter
Regulates rate of gas flow

23. FIGURE 15-21 Schematic of a GTA welding setup with a water-cooled torch.
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24. FIGURE 15-22 Schematic of a GTA welding setup with an air-cooled torch.
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25. Types of Welding Current
GTA welding
All three types can be used
DCEN: concentrates about 2/3 of its welding heat on the work
DCEP: concentrates about 1/3 of its welding heat on the work
AC: concentrates about 1/2 of its heat on the work

26. FIGURE Electrons collect under the oxide layer during the DCEP portion of the cycle and lift the oxides from the surface.
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27. Shielding Gases GTA welding process shielding gases Argon (Ar)
Helium (He)
Hydrogen (H)
Nitrogen (N)
Mixture of two or more gases

28. Shielding Gases (cont'd.)
Key concepts
Argon
Effectively shields welds in deep grooves in flat positions
Helium
Advantage of deeper penetration
Hydrogen
Not an inert gas
Not used as primary shielding gas

29. Shielding Gases (cont'd.)
Nitrogen
Not an inert gas
Has been used as an additive to argon
Hot start
Allows a surge of welding current

30. Preflow and Postflow Preflow Postflow
Time gas flows to clear out air in the nozzle or weld zone
Some machines do not have preflow
Postflow
Time gas continues flowing after welding current has stopped
Protects molten weld pool, filler rod, and tungsten electrode as they cool

31. Shielding Gas Flow Rate
Measured in cubic feet per hour (CFH) or in metric measure as liters per minute (L/min)
Rate of flow should be as low as possible and still give adequate coverage
TABLE 15-4 Suggested Argon Gas Flow Rate for Given Cup Sizes.

32. Remote Controls Can be used to: Remote Start the weld Increase current
Decrease current
Stop the weld
Remote
Foot-operated or hand-operated device

33. Summary Prime considerations for gas tungsten arc welding
Equipment cleanliness
Everything is clean: welding process proceeds more easily
Tungsten end or tip shape
Contamination can be very frustrating
Tungsten contamination is part of the process