1. Gas Tungsten Arc Welding (GTAW) (TIG)

3. Uses high quality welds - good seal
root bead for heavy pipe in petroleum, chemical industry
flange joints designed for no filler metal
seldom used for metals over 1/4” thick - if so, just a root pass
metals as thin as .003”

4. Filler metal added manually
occasionally automatically

5. Requires more welder skill - handle electrode and torch

6. Adv: small HAZ - less weakening no metal transfer through arc
no splattering
quiet
high quality

7. Power supply
AC / DCEP / DCEN (most common)

8. DCEN (most common)
70% at work piece while 30% at electrode = deeper penetration

9. DCEP - less heat - ok for thin metal

10. Breaking up surface oxides
occurs with DCEP and 1/2 AC cycle
+ charged shielding gas ions are flowing from nozzle to (-) charged work
these ions strike the work surface with enough force to break up oxides
works well for magnesium and aluminum

12. Always done with Constant Current power supply
same as for SMAW
varying arc length allows slight variations in the current
Current setting determined by
size of electrode
metal thickness
shielding gas used
type of current supplied

13. Torch - 4 functions 1. hold electrode
2. electrical contact with electrode
3. direct shielding gas to weld
4. provide means to cool electrode

15. Torch nozzles
ceramic
exit dia of nozzle and lengths vary depending on mfgr.
single digit number ID’s the nozzle exit dia. in 1/16” increments
a #6 = 6 x 1/16” = 3/8”
a #8 = 8 x 1/16” = 1/2”
nozzle dia must allow complete coverage of weld area with shield gas

17. Small exit diameter

18. Other torch parts
Collet - supports electrode

19. Shield gas protects electrode from contamination
oxygen, nitrogen in air, dirt
**allow gas to flow after arc has stopped seconds

20. Shielding gases
argon - smoother, quieter, better cleaning, heavier than air
helium - more heat at work piece, gives deeper penetration
mixtures of the two

21. Gas flow rates being equal at 14 CFPH #8 nozzle - smooth flow
#4 nozzle - rapid flow
about 35 CFPH recommended for mild steel

22. Tungsten electrodes 100% tungsten - green band -
tungsten with 1% thoria added - yellow band
tungsten with 2% thoria added - red band (common)
tungsten with .15 to .40 % zirconia added - brown band
pure tungsten with a core of 1 to 2% thoria added - blue band

23. Thoria & zirconia helps to harden the electrode
facilitate arc starting
help maintain a stable arc

24. Electrode sizes
diameters .010” to .025”
lengths 6 - 7” up to 24”

25. Electrode extension at end of nozzle or up to 1/2” extension
determined by shape of joint
longer extension = more gas flow rate

26. Electrode Tips

27. Conical - for DCEN
produces a concentrated, hotter arc - deeper penetration
70% of heat developed at work so tip will not melt
sharpen with 80 to 120 grit

28. Rounded - used for AC and DCEP
Welding al. or magnesium
electrode forms a ball at tip - arc flows more easily
smoother transition through cycle from cleaning to penetration
smoother weld bead

30. Filler metal bare wire - coils or precut lengths
common dia of 1/16” to 1/4”
cannot withdraw from shielding gas envelope while molten

31. Torch and filler position

32. Method of adding filler metal

33. Joint designs same as for SMAW

34. Hot shortness metals like al. become very weak and melt through
use backing plate

35. Methods of starting arc
1. scratch
2. superimposed high frequency current
3. high voltage

36. Safety same as for SMAW and GMAW
infrared rays may be more intense when using larger electrodes

37. Automation