Projection welding is a variation of spot welding. Projections are designed in one part. These act as current concentrators for the welding process. When the two parts are mated together, these projections are the high points that first make contact. As the power is cycled, the projections simultaneously carry the current and are welded. This process is known as Resistance Projection Welding, RPW.
Due to the efficiency of power transfer, thicker materials can be successfully welded. Materials as thick as 3 mm (0.125 in) can be successfully welded. For thin stock, the traditional spot welding is a preferred method.
Low carbon steels, low alloy steels, stainless steels, as well as aluminum can be welded using this process.
Projections are usually semi-spherical or blunt conical type.
Projection welding requires that the height of projections be controlled to within a range of 0.075 mm (0.003 in).