How does resistance spot welding create heat?

• A. By electrical resistance between two metal sheets under pressure
• B. By laser irradiation
• C. By friction
• D. By chemical reaction

Answer: (A)

Heat in resistance spot welding comes from converting electrical energy into heat within the joint. A high current is forced through the overlap of two metal sheets held together by electrodes. The metal naturally resists the current, especially at the tiny contact area where oxides and impurities are present, so electrical energy is dissipated as heat (I^2R heating) right at that spot. That localized heating raises the temperature until the metal melts and can fuse under the applied pressure, forming a weld nugget. The pressure is essential to maintain contact, squeeze out trapped air and oxides, and help shape and solidify the nugget as it cools. This heat source is different from laser, friction, or chemical heat—those methods rely on different mechanisms, whereas resistance spot welding uses the metal’s own resistance to electric current to create the weld.