1. Gas Tungsten Arc Welding of Plate
Chapter 16
Gas Tungsten Arc Welding of Plate

2. Objectives
Name the applications for which the gas tungsten arc welding process is more commonly used
Discuss the effects on the weld of varying torch angles
Explain why the filler rod end must be kept inside the protective zone of the shielding gas and how to accomplish this
Tell how tungsten contamination occurs and what should be done when it happens

3. Objectives (cont'd.)
Explain what can cause the actual welding amperage to change
Determine the correct machine settings for the minimum and maximum welding current for the machine used, the types and sizes of tungsten, and the metal types and thicknesses
List factors that affect the gas preflow and postflow times required to protect the tungsten and the weld

4. Objectives (cont'd.)
Determine the minimum and maximum gas flow settings for each nozzle size, tungsten size, and amperage setting
Compare the characteristics of low carbon and mild steels, stainless steel, and aluminum in respect to GTA welding
Describe the metal preparation needed before GTA welding

5. Objectives (cont'd.)
Demonstrate how to properly make GTA welds in butt joints, lap joints, and tee joints in all positions that can pass the specified standard

6. Introduction Gas tungsten arc welding Also called GTA welding
Can be used to for nearly all types and thicknesses of metal
Fluxless, slagless, and smokeless
Welders have fine control of the welding process
Used when appearance is important
Setup of equipment affects weld quality
Charts give correct settings
Field conditions affect the variables

7. Torch Angle
Key points
Torch should be held as close to perpendicular as possible
May be angled zero to fifteen degrees from perpendicular for better visibility
As the gas flows out it must form a protective zone around the weld
Too much tilt distorts protective shielding gas zone
Velocity of shielding gas affects protective zone as torch angle changes

8. Filler Rod Manipulation
Filler rod must be kept inside the protective zone
If removed from the gas protection
Oxidizes rapidly: oxide is added to weld pool
Rod tip becomes oxidized: cut it off
Weld is temporarily stopped
Shielding gas must be kept flowing
Rod should enter shielding gas as close to base metal as possible
Angles under 15 degrees prevent air from being pulled in welding zone

9. FIGURE 16-2 The hot filler rod end is well within the protective gas envelope.
Larry Jeffus

10. FIGURE 16-5 Filler being remelted as the weld is continued.
Larry Jeffus

11. Tungsten Contamination
Most frequent problem
Tungsten becomes contaminated if it touches molten weld pool or filler metal
Surface tension pulls contamination up onto the hot tungsten
Extreme heat causes some of the metal to vaporize and form a large oxide layer

12. FIGURE 16-8 Contaminated tungsten.
Larry Jeffus

13. Tungsten Contamination (cont'd.)
Contamination forms a weak weld
Weld and tungsten must be cleaned before any more welding can be done
Tiny tungsten particles will show up if the weld is X-rayed
Contamination can be knocked off quickly by flipping the torch head

14. FIGURE 16-8 Contaminated tungsten.
Larry Jeffus

15. Current Setting
Amperage on machine's control is the same at the arc when:
Power to machine is exactly correct
Lead length is very short
All cable connections are perfect
Arc length is exactly right
Remote current control is in full on position

16. Experiments Designed to help new welders learn basic skills Learn more
Help troubleshoot welding problems
Learn more
Subtle changes will become more noticeable
Even experienced welders make changes

17. Figure 16-10 Melting first occurring.
Larry Jeffus

18. Gas Flow Gas preflow and postflow times depend upon:
Wind or draft speed
Nozzle size
Tungsten size
Amperage
Joint design
Welding position
Type of metal welded
Maximum flow rates must never be exceeded

19. Practice Welds Grouped according to weld position and type of joint
Mild steel
Inexpensive
Requires the least amount of cleaning
Aluminum
Cleanliness is a critical factor
Try each weld with each metal
Determine which metal will be easier to master

20. Low Carbon and Mild Steels
Two basic steel classifications
Most common
During manufacturing small pockets of primary carbon dioxide gas become trapped
Do not affect strength
Porosity: likely when not using a filler metal
Most filler metals have some alloys (i.e., deoxidizers)
Prevent porosity caused by gases trapped in base metal

21. Stainless Steel Setup and manipulation
Nearly the same as for low carbon and mild steels
Welds show effects of contamination
Precleaning is important
Most common problem
Bead color after the weld
Using a low arc current with faster travel speeds is important
Carbide precipitation

22. Aluminum Molten aluminum weld pool
High surface tension
Preheat base metal in thick sections
Preheat temperature is around 300 degrees Fahrenheit
Cleaning and keeping the metal clean
Time consuming
Aluminum resists oxidation at room temperature
Rapidly oxidizes at welding temperatures

23. FIGURE 16-15 Aluminum filler being correctly added to the molten weld pool.
Larry Jeffus

24. Metal Preparation Base and filler metals Must be thoroughly cleaned
Contamination will be deposited into the weld
Oxides, oil, and dirt are the most common
Contaminants can be removed mechanically or chemically

25. Summary
Position yourself to control the electrode filler metal and to see the joint
Experienced welders realize they need to see only the leading edge of the weld pool
Good idea to gradually reduce your need for seeing 100% of the weld pool
Increasing this skill is significant advantage
Welding in the field
May have to be done out of position