1. Gas Tungsten Arc Welding

3. Objectives Describe the gas tungsten arc welding process
List other terms used to describe it
What makes tungsten a good electrode
Eliminate tungsten erosion
Shape and clean a tungsten electrode
Grind a point on a tungsten electrode

4. Objectives (continued)
Remove a contaminated tungsten end
Melt the end of the tungsten electrode into the desired shape
Compare water-cooled GTA welding torches to air-cooled torches
The purpose of the three hoses connecting a water-cooled torch to the welding machine

5. Objectives (continued)
Choose an appropriate nozzle
How to get an accurate reading on a flowmeter
Compare the three types of welding current used for GTA welding
Shielding gases used in the GTA welding process

6. Objectives (continued)
Define preflow and postflow
Problems resulting from an incorrect gas flow rate
Properly set up a GTA welder
Establish a GTA welding arc

7. Introduction
The Gas Tungsten Arc Welding (GTAW) process is sometimes referred to as a TIG or Heliarc
TIG is short for tungsten inert gas
An arc is established between a non-consumable tungsten electrode (heating element) and the base metal
The inert gas provides the needed arc characteristics and protects the molten weld pool
When Argon became plentiful, the GTA process became more common

8. Power Source Basics

10. Tungsten Electrodes

11. Tungsten Tungsten has the following properties: High tensile strength
Hardness
High melting temperature
High boiling temperature
Good electrical conductivity

12. Tungsten (continued)
Tungsten is the best choice for a non consumable electrode
High melting temperature
Good electrical conductivity
As the tungsten electrode becomes hot the arc between the electrode and the work stabilizes
But a clean and correctly ground tungsten is needed
Because of the intense heat some erosion of the electrode will occur

13. Figure 15-1 Some tungsten will erode and be transferred across the arc.

14. Tungsten (continued) Ways to limit erosion:
Good mechanical and electrical contact
Use as low a current as possible
Use a water-cooled torch
Use as large a tungsten electrode as possible
Use DCEN current
Use as short an electrode extension as possible
Use the proper shape electrode
Use an alloyed tungsten electrode

15. Torch Build Out

16. Torch Build Out

17. Tungsten (continued)
The collet is the cone-shaped sleeve that holds the electrode in the torch
Large-diameter electrodes conduct more current
The current-carrying capacity at DCEN is about ten times greater than at DCEP
The preferred electrode shape impacts the temperature and erosion of the tungsten
With alternating current, the tip is subjected to more heat than with DCEN

18. Figure 15-3 The smooth surface of a centerless ground tungsten electrode. Courtesy of Larry Jeffus.

19. Types of Tungsten Electrodes
Pure tungsten is an excellent nonconsumable electrode
Pure tungsten can be improved by adding:
Cerium
Lanthanum
Thorium
Zirconium

20. Tungsten Electrodes

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

22. Shaping the Tungsten To obtain the desired end shape:
Grinding (for MS and SS)
Breaking (not recommended due to cost)
Re melting the end (Aluminium welding)
Using chemical compound (doesn’t work that well)

23. Grinding
Often used to clean a contaminated tungsten or to point the end
Should have a fine, hard stone
A 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

24. Figure 15-8 Correct way of holding a tungsten when grinding
Figure 15-8 Correct way of holding a tungsten when grinding. Courtesy of Larry Jeffus.

25. Breaking and Remelting
Tungsten is hard but brittle
If struck sharply, it will break without bending
Try not to do this because of $$$$$$$$
Holding against a sharp corner and hitting results in a square break
After breaking squarely, melt back the end

26. 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
When the tungsten is removed, cooled, and cleaned, the end will be tapered to a fine point
The chemical compound will dissolve the tungsten, allowing the contamination to fall free

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

28. Figure 15-14 Melting the tungsten end shape.

29. GTAW Equipment

30. GTA Welding Equipment “Cadillac Stick Welder”
GTA welding torches are water- or air-cooled
Water-cooled GTA welding torch is more efficient
Water-cooled torch has three hoses connecting it to the welding machine
Nozzle directs the shielding gas directly on the welding zone
Flowmeter regulates the rate of gas flow

31. Figure 15-21 Schematic of a GTA welding setup with a water-cooled torch.

32. Types of Welding Current
DCEN concentrates about 2/3 of its welding heat on the work
Max penetration
High Freq. – start only
DCEP concentrates about 1/3 of its welding heat on the work
Max cleaning action
2/3 of heat at tungsten – primarily used for balling tungsten for aluminium welding

33. Types of Welding Current
AC concentrates its heat at 50/50
Sign wave provides for DCRP (cleaning action) and DCSP (penetration action)
Square wave technology allows for adjusting the cleaning or penetration cycle.
High Freq. is on Continuous so there is equal firing of both sides of sign wave.
DC Component will take place if there is no High Freq.

34. Figure 15-29 Electrons collect under the oxide layer during the DCEP portion of the cycle.

35. Figure 15-30 Sine wave of alternating current at 60 cycle.

36. Shielding Gas

37. Shielding Gases Shielding gases used for GTA welding process:
Argon (Ar)
Helium (He)
Or a mixture of two or more gases

38. Shielding Gases (continued)
Argon effectively shields welds in deep grooves in flat positions
Helium offers the advantage of deeper penetration

39. Shielding Gases (continued)
Hot start allows a surge of welding current
Preflow is the time gas flows to clear out air in the nozzle
Some machines do not have preflow
Postflow is the time the gas continues flowing after the welding current has stopped

40. Shielding Gases (continued)
Ionization Potential
Amount of voltage needed to “kick start” the arc
The ionization potential, or ionization energy, of a gas atom is the energy required to strip it of an electron. That is why a shielding gas such as helium, with only 2 electrons in its outer shell, requires more energy (higher voltage parameters) for welding. The ionization potential of a shielding gas also establishes how easily an arc will initiate and stabilize. A low ionization potential means the arc will start relatively easy and stabilize quite well. A high ionization potential has difficulty initiating and may have difficulty keeping the arc stable.
Argon
15.7 electron volts
Helium
24.4 electron volts
More penetration

41. Figure 15-35 Too steep an angle between the torch and work may draw in air.

42. Remote Controls Foot or Finger

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

44. Welding Techniques

45. Objectives Applications using the gas tungsten arc welding process
Effects on the weld of varying torch angles
Why and how the filler rod is kept inside the protective zone of the shielding gas
How tungsten contamination occurs and what to do
Causes of change in welding amperage
Correct settings for the minimum and maximum welding current

46. Objectives (continued)
Types and sizes of tungsten and metal
Factors affecting gas preflow and postflow times
Minimum and maximum gas flow settings:
Nozzle size
Tungsten size
Amperage setting
Characteristics of low carbon and mild steels, stainless steel, and aluminum
Metal preparation for GTA welding
Make GTA welds in all positions

47. Introduction Gas tungsten arc is also called GTA welding
GTA welding can be used to for nearly all types and thicknesses of metal
GTA welding is fluxless, slagless, and smokeless
Welders have fine control of the welding process
GTA welding is ideal for close-tolerance welds
Some GTA welds make the critical root pass
GTA used when appearance is important

48. Introduction (continued)
Setup of GTA equipment affects weld quality
Charts give correct settings
Field conditions affect the variables in the charts
Experiments designed to evaluate the appearance of a weld
After welding in the lab, troubleshooting field welding problems is easier
To make a weld is good: to solve a welding problem is better

49. Torch Angle As close to perpendicular as possible
May be angled 0-15 degrees from perpendicular for better visibility
As the gas flows out it forms a protective zone around the weld
Too much tilt distorts protective shielding gas zone

50. Figure 16-5 Filler being remelted as the weld is continued
Figure 16-5 Filler being remelted as the weld is continued. Courtesy of Larry Jeffus.

51. Torch Angle (continued)
Velocity of shielding gas affects protective zone
Low-pressure area develops behind the cup when velocity increases
Sharper angle and higher flow rate increases contamination

52. Filler Rod Manipulation
Filler rod must be kept inside the protective zone
If filler rod is removed from the gas protection, it oxidizes rapidly
Oxide is added to the molten weld pool
When a weld is temporarily stopped, the shielding gas must be kept flowing

53. Filler Rod Manipulation (continued)
If the rod tip becomes oxidized, if should be cut off before restarting
The rod should enter the shielding gas as close to the base metal as possible
An angle less than 15 degrees prevents air from being pulled in the welding zone

54. Figure The hot filler rod end is well within the protective gas envelope. Courtesy of Larry Jeffus.

55. Figure 16-7 Too much filler rod angle has caused oxides to be formed on the filler rod end. Courtesy of Larry Jeffus.

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

57. Tungsten Contamination (continued)
Contamination caused by the tungsten touching the molten pool or filler metal forms a weak weld
The 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
This procedure should never be used with heavy contamination or in the field

58. Figure 16-8 Contaminated tungsten. Courtesy of Larry Jeffus.

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

60. Figure 16-10 Melting first occurring. Courtesy of Larry Jeffus.

61. Figure 16-12 Oxides forming due to inadequate gas shielding
Figure Oxides forming due to inadequate gas shielding. Courtesy of Larry Jeffus.

62. Gas Flow Gas preflow and postflow times depend upon:
Wind or draft speed
Tungsten size used
Amperage
Joint design
Welding position
Type of metal welded
Maximum flow rates must never be exceeded
Air can be sucked into the weld zone

63. Practice Welds
Practice welds are grouped according to the weld position and type of joint
Mild steel is inexpensive and requires the least amount of cleaning
With aluminum, cleanliness is a critical factor
Try each weld with each metal to determine which metal will be easier to master

64. Low Carbon and Mild Steels
Low carbon and mild steel are two basic steel classifications
Small pockets of primary carbon dioxide gas become trapped
Porosity most likely when not using a filler metal
Most filler metals have some alloys, called deoxidizers

65. Stainless Steel
Setup and manipulation are nearly the same as for low carbon and mild steels
Most welds on stainless steels show effects of contamination
Most common problem is the bead color after the weld
Using a low arc current with faster travel speeds is important

66. Aluminum Molten aluminum weld pool has high surface tension
Preheat the base metal in thick sections
Preheat temperature is around 300° Fahrenheit
Cleaning and keeping the metal clean is time consuming
Aluminum rapidly oxidizes at welding temperatures

67. 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

68. Figure Aluminum filler being correctly added to the molten weld pool. Courtesy of Larry Jeffus.

69. Figure Filler rod being melted before it is added to the molten pool. Courtesy of Larry Jeffus.

70. Figure 16-18 Surfacing weld. Courtesy of Larry Jeffus.

71. Figure 16-20 Establish a molten weld pool and dip the filler rod into it. Courtesy of Larry Jeffus.

72. Figure Note the difference in the weld produced when different size filler rods are used. Courtesy of Larry Jeffus.

73. Figure 16-22 Move the electrode back as the filler rod is added
Figure Move the electrode back as the filler rod is added. Courtesy of Larry Jeffus.

74. Figure 16-34 Be sure both the top and bottom pieces are melted
Figure Be sure both the top and bottom pieces are melted. Courtesy of Larry Jeffus.

75. Figure 16-35 Oxides form during tack welding. Courtesy of Larry Jeffus.

76. Figure 16-36 A notch indicates the root was not properly melted and fused. Courtesy of Larry Jeffus.

77. Figure 16-37 Watch the leading edge of the molten weld pool
Figure Watch the leading edge of the molten weld pool. Courtesy of Larry Jeffus.

78. Summary
Positioning yourself to control the electrode filler metal and to see the joint is critical
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 in the field
Welding in the field may have to be done out of position