1-Why do we use Alternating Current to weld Aluminum? (top)
Alternating current alternates between electrode positive and electrode negative. When the tungsten electrode is positive the aluminum oxide on the surface is being cleaned and most of the heat in the arc is concentrated on the tungsten. When the electrode is negative the arc penetrates but very little heat is concentrated on the tungsten. We could use DC electrode positive to weld aluminum but a very large tungsten electrode would be required. By alternating (AC current) between positive and negative we can clean the aluminum surface without using too large a tungsten electrode.
2-What is high frequency? (top)
High frequency is very low amperage, high voltage current, which is super, imposed on the main welding current coming out of the welding machine. Traditional AC current is not too stable and the arc tends to go out. The high frequency helps to keep the arc lit when it wants to go out. It also helps to start or initiate the welding arc.
3-What type of tungsten electrode is recommended? (top)
For AC welding of Aluminum with older sine wave type machines use pure tungsten or Zirconium doped tungsten. For advanced square wave machines such as the Miller Dynasty use the ceriated or lanthanated tungsten's. For welding with DC electrode negative use the thoriated electrodes. Thoria however is radioactive so if a non-radioactive tungsten is requested then either the lanthanated or ceriated tungsten should be used.
4-What amperage should be used to weld a specific thickness of material? (top)
A rule of thumb would be roughly one ampere of current for every .001 inches of thickness of the base material.
5-How long should the post-flow of shielding gas run? (top)
The post flow should last a second for every 10 amps of welding current. So if you are welding at 150 amps you should have approximately 15 seconds of post flow. The tungsten should be shiny or silvery in color after welding and not have a blue or black color.
6-Can I use other gases than argon for TIG welding? (top)
For Aluminum; argon or argon helium mixes such as ALTIGTM, BlueshieldTM 1,2, or 3 can be used. This helps when looking for higher welding speeds or when welding thicker materials. For austenitic stainless steels of the 300 series argon-hydrogen mixes such as BlueshieldTM 11 and 12 can be used. They give faster welds and cleaner weld bead appearance.
7-Where should I use TIG welding versus stick or MIG welding? (top)
TIG welding has the potential to produce the highest quality of welds and welds without spatter and excellent appearance. It is however the slowest of the three processes. MIG welding can weld thin material with ease (much easier than stick) but you cannot weld as thin a material as with the TIG process. MIG also tends to produce spatter. Stick welders are the lowest cost to purchase but it requires skill to weld thin material (gauge thicknesses) and it requires more clean up because of the spatter and the slag.