GMA Welding for Collision Repair Practice Test 2026 - Complete Exam Prep

Polarity in GMAW controls heat distribution and arc behavior, so it strongly influences weld penetration and bead quality. Using direct current with the electrode as the positive terminal directs most of the arc heat into the workpiece, which increases penetration and produces a stable arc when welding steel with a solid wire and shielding gas. This combination is well-suited to the common transfer modes (like spray or short-circuit) used on steel and helps ensure proper fusion and a solid bead in collision repair welds. If the electrode were negative, more heat would go into the wire and penetration would be reduced, potentially causing weak fusion and more spatter. Alternating current changes polarity continuously and isn’t the standard choice for this setup on steel with shielding gas. And welding without shielding gas defeats the process entirely, since the gas protects the weld from contamination; even with DC+, lacking shielding gas would compromise weld quality.