Which tungsten tip shape is typically used for AC welding?

• A. Sharp point
• B. Flat tip
• C. Rounded (ball) tip
• D. Tapered

Answer: (C)

In AC TIG welding, you want an arc that is stable and forgiving as the polarity reverses each cycle, and you also want good cleaning action for the oxide layer on aluminum. A rounded (ball) tungsten tip achieves this by presenting a larger contact area, which creates a broader, more stable arc and helps with the oxide removal process during the AC cycle. This reduces arc wandering and makes it easier to control the weld puddle on aluminum.

A sharp point concentrates heat into a small spot, which can make the AC arc harder to control and increase the risk of instability or contamination. A flat tip concentrates heat even more in a single plane, and a tapered tip changes the arc characteristics in ways that aren’t ideal for typical AC TIG welding. So the rounded tip is the typical, best choice for AC welding.