How does resistance spot welding create heat?

• A. By arc heating
• B. By flame heating
• C. By laser heating
• D. By electrical resistance between two metal sheets under pressure

Answer: (D)

Heat in resistance spot welding comes from electrical resistance at the interface where the two overlapping metal sheets are pressed together by the electrodes. A very high current flows through that small contact area, and the energy dissipated there as I^2R heating raises the temperature rapidly. This localized heating melts the metal surfaces so they can fuse together to form a weld nugget as the current is stopped and the pieces are pressed together. The pressure is essential: it creates intimate contact for a consistent current path and concentrates the heat at the intended spot, while also aiding metal flow and solidification into a strong joint. This process relies on converting electrical energy directly into heat at the contact interface, unlike arc, flame, or laser heating, which use an external heat source.