In contrast to argon, helium is the lightest of the inert gases. Because of its light weight, about two to three times more helium is needed as compared to argon to shield the weld area. Despite this, helium has an advantage over argon in that it can be used with greater arc voltages.
Because of this, helium is preferred when working with thick metal sections.
Another difference in the two gases is their cleaning ability. Both helium and argon allow for good cleaning action when using DC. However, when using AC, argon provides for better cleaning action. Argon also provides better arc stability than helium when using AC.
Proper Gas Selection
You want to make sure to use the right gas with TIG. Usually, pure argon is used, although thicker welding may require an argon/helium or other specialty mix. If you use the wrong gas mixture, such as a 75 percent argon/25 percent CO2 that is common for MIG, the tungsten electrode will quickly be consumed or deposited in the weld puddle.
Gas Flow Rate
Setting a proper gas flow rate is another important element to successful TIG welding. Contrary to what may seem to be common sense, more isn’t better. If you are welding in a flat position, a flow rate of about 15 to 20 cubic feet per hour (cfh) is typically adequate. For overhead welding, you can start at about 20 cfh and increase the flow by small adjustments of about 5 cfh if necessary.
So why is too high a flow rate a bad thing? Well, if the gas flows out of the torch at too high a velocity, it ends up bouncing off the surface being welded and starts a swirling motion parallel to the torch cup called a venturi. This venturi effect will suck air into the gas flow, creating an impure weld atmosphere. This results in pinholes in the weld.
A TIG torch can either be air cooled or water cooled. If most of the welding you do is at 200 amps or less, an air-cooled torch is adequate. If welding above 200 amps, a water-cooled torch should be considered.
Controls are also offered in either foot pedal control or torch control. Foot pedal control tends to be more popular where work is done in an area that affords mobility. A fingertip control can be beneficial when working in an awkward position or where less mobility is available.
Many different electrode types are available including thoriated, lanthaniated, ceriated, and pure tungsten. When choosing an electrode, follow manufacturers’ recommendations and choose the one that is best for you. Some characteristics to consider in an electrode are good ignition and re-ignition properties, constant arc, long lifetime, and high current-loading capacity.
Good Welding Practices
You want to get in as comfortable a position as possible. Brace your arm to allow for steady torch movement. Many TIG welders hold the torch like a pencil to afford them the best control.
You want to hold the torch at the proper angle. If the torch is perpendicular to the work piece, it will be difficult to view the welding process.
The angle of the torch relative to perpendicular should be about 15 to 20 degrees. If this angle is exceeded too much, it can lead to less penetration, poor shielding gas coverage, and general arc instability.
In regards to travel direction, the torch should be pushed away from (ahead of) the weld puddle. This ensures proper gas coverage of the weld puddle and offers the welder a good view of the weld puddle.
Properly cleaning the area you will be welding is critical to a good weld result. Mike Sammons, sales and marketing manager for Weldcraft, points out, “Cleaning aluminum before GTA welding is essential to avoid contaminates, which can lead to lack of fusion, inclusions or porosity.” Be sure to wipe the base metal to remove any dirt, oil, grease or other contaminates.
When welding aluminum it is especially important to remove the oxides that naturally form on the surface. Aluminum oxide is the result of aluminum wanting to return to its natural state. Bare aluminum will oxidize as soon as it is exposed to the atmosphere, creating aluminum oxide.
Aluminum oxide is very hard (the only thing harder is a diamond). Its melting point is about three times that of aluminum. If not removed, it can lead to contaminated weld puddles or even prevent a weld puddle from properly forming.