In AC GTAW, how is heat distributed between the positive and negative half-cycles?

• A. No impact on cleaning, but increases penetration
• B. Half heat on each half-cycle, yielding balanced cleaning action and penetration
• C. All heat on the positive half-cycle
• D. All heat on the negative half-cycle

Answer: (B)

AC GTAW uses a waveform that reverses polarity every half-cycle, so the arc delivers heat with roughly equal time in each direction. That means about half the heat goes into the weld area during the positive half-cycle and about half during the negative half-cycle. The result is a balance: the positive half-cycle promotes cleaning of the surface oxide, while the negative half-cycle provides the depth of penetration. Many power sources let you adjust this balance to favor cleaning or penetration as needed. If all heat were on one side, you'd sacrifice either cleaning action or penetration, which is not how AC TIG is intended to operate.