The side seam welder welds tinplate, stainless steel, black plate and edge-ground T.F.S. bodies by using copper wire as an intermediate electrode between the welding rollers and only three working operations are necessary i.e. blank cutting, roll-forming and seam welding. The individual operations for seam welding such as body clamping, feeding, switching on and off the welding-current are carried out automatically on the machine.