Importance

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Abstract

A spot welding machine comprising a first electrode and a second electrode opposed to the first electrode, whereby a workpiece, including, e.g., a conductor wire coated with a heat-resistant resin film and a terminal to be welded to the conductor wire, is subjected to electric-resistance welding in a manner such that the workpiece is held between the first and second electrodes. In the spot welding machine according to the present invention, a third electrode is interposed between the first electrode and the workpiece so that one distal-end side face of the third electrode abuts closely against a workpiece engaging end of the first electrode, and that the other distal-end side face of the third electrode is in contact with the workpiece. The proximal end of the first electrode is connected to a first terminal of AC power source means, and the respective proximal ends of the second and third electrodes are connected to a second terminal. The AC power source means supplies a current, used to heat the third electrode and remove the resin coating film by fusion, to a closed circuit having a route essentially consisting of the first terminal, first electrode, third electrode, and second terminal, during a predetermined period. After the removal of the coating film, the AC power source means supplies a current, used to weld the workpiece, to a closed circuit having a route essentially consisting of the first terminal, first electrode, third electrode, workpiece, second electrode, and second terminal.

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First Claim