A resistance welder is a method in which a welded workpiece is pressed between two electrodes and heated to a molten or plastic state by electrical current passing through the contact surface of the workpiece and the resistive heat generated in the adjacent area. In spot welding, the workpiece is "spot" welded to only a limited number of contact surfaces, forming a flat, spherical nucleus. Spot welding can be divided into single spot welding and multi-spot welding. In multi-spot welding, more than two pairs of electrodes are used in the same process to form multiple cores.
Seam welding is similar to spot welding. In seam welding, a continuous weld is formed before and after the workpiece passes between two rotating disc-shaped electrodes (rollers) to form a strip weld joint. A projection weld is a variation of a spot weld. The workpiece has prefabricated bumps. When convex welding, one or more fusion cores can be formed at the joint at a time. When welding, the ends of two workpieces are in contact with each other and are welded along the entire contact surface after resistance heating and pressure.
The resistance welding machine has the following advantages：
(1) When the molten nucleus is formed, it is always surrounded by a plastic ring, the molten metal is isolated from the air, and the metallurgical process is simple.
(2) Short heating time, concentrated heat, small heat-affected area, small deformation stress, no need to arrange calibration and heat treatment process after welding.
(3) Metal, oxygen, acetylene, argon and other welding materials do not need welding wire, welding rods and other fillers, welding costs are low.
(4) Simple operation, easy mechanization and automation, improve labor conditions.
(5) High productivity, no noise and harmful gases. In mass production, it can be woven into the assembly line along with other manufacturing processes. However, isolation flash welding is required due to sparks flying.