Practical Welding Today - March/April 2009

A well-done GTAW on anodized aluminum can result in an excellent cosmetic appearance.

Although easily described, bumping is one of the more difficult GTAW techniques to master. A proficient operator typically can reach a travel speed of about an inch every 30 to 40 seconds.

The amperage range you use will depend on your skill, with a beginner to intermediate welder using around 180 to 190 amps, and a highly skilled welder around 230 amps.

The thickness of the material will require you to adjust the travel speed—thin material requires a faster travel speed than thicker material—but the amperage range typically remains the same regardless of material thickness.

At those amperage levels, a filler metal of ¹⁄8 in. diameter should be used. Anything smaller will melt off before it gets to the weld pool. It is also important when adding the filler metal to insert it at the leading edge of the weld pool while the arc is live and to remove it before extinguishing the arc, so that the filler metal doesn’t become trapped in the weld pool as it cools.

The distance between the end of the filler metal and the weld should be no more than the diameter of the torch cup.

Although anodized aluminum certainly poses some unique challenges, its weight, low cost, and resistance to corrosion make it the best option for many applications and environments. Following this advice should help you overcome the difficulties associated with this material and realize its potential benefits. ■