What is spot welding?

• A. A friction-based welding method that uses rotating tools.
• B. A process that joins metal by spot welding using nuggets of fused metal produced by resistance heating at the interface.
• C. A laser-based process forming a continuous weld bead along a seam.
• D. A riveting process that uses mechanical fasteners.

Answer: (B)

Spot welding is a resistance welding process in which two metal sheets are pressed together and joined by heat generated at the interface from electrical resistance. The current passes through the overlapped pieces, and the contact resistance at the interface concentrates heating there, melting a small region to form a nugget that fuses the sheets as it cools. The electrodes shape the weld area and apply pressure to ensure a solid bond and to control expulsion of molten metal. This method is fast, economical for thin sheets, and well-suited to joining common automotive and fabrication steels. It isn’t a friction-based welding process, which uses rotating tools to generate heat, nor a laser-based seam weld, which uses a laser to form a continuous weld bead, nor a riveting process, which relies on mechanical fasteners without melting.