Which statement best describes projection welding?

• A. Heating is localized at predetermined points by design.
• B. Heating occurs uniformly across the entire surface.
• C. Heat is generated only after the parts are pressed fully.
• D. It cannot join sheet metal to other parts.

Answer: (A)

Projection welding concentrates heat at designed protrusions on the workpieces, so the electrical resistance heating occurs mainly at those small, pre-made contact points. The raised features (nipples, dimples, etc.) create very small contact areas, which raises current density there. With the current flowing during the clamping and pressing cycle, those points heat rapidly, soften, and fuse to form weld nuggets right at the projections. This is why heating is localized at predetermined points by design rather than spreading across the entire surface.

That focused heating is what makes projection welding efficient and reliable: you can weld multiple points at once or weld sheet metal to a thicker piece or to hardware without heating the whole area, and you can achieve consistent welds even with minor variations in thickness. The statement describing localized heating at designed points best captures this process. The other statements don’t fit because heating is not uniform across the surface, the heat is generated during the weld cycle as the parts are clamped and current flows—not only after full pressing, and projection welding is indeed used to join sheet metal to other parts.