 Spot welding is a popular resistance welding method used to join overlapping metal sheets of up to 3 mm thick . Two electrodes are simultaneously used to clamp the metal sheets together and to pass current through the sheets . The advantages of the method include efficient energy use , limited workpiece deformation , high production rates , easy automation , and no required filler materials . Weld strength is significantly lower than with other welding methods , making the process suitable for only certain applications . It is used extensively in the automotive industry — ordinary cars can have several thousand spot welds made by industrial robots . A specialized process , called shot welding , can be used to spot weld stainless steel . 
