Measurement and effect of contact resistance in spot welding

SPOT WELDING consists essentially of clamping two pieces of sheet metal between two copper electrodes and passing through the pieces an electric current of sufficient strength to fuse them together at the spot where the current is most concentrated. Spot welding is the simplest of the electric resistance-welding processes which depend upon the Joule effect, H = I²RT, for the generation of heat. The total resistance, R, in spot welding consists of the body resistance of the metal between the electrodes plus the sum of the sheet-to-sheet and electrode-to-sheet contact resistances. The purpose of this paper is to report to the electrical-engineering profession on recent investigations of the electrical resistance of these contacts and the importance of these resistances in the spot-welding process.