Abstract: A sheet metal repair jig for smoothening a sheet metal by heating and cooling a part of the sheet metal to be repaired includes at least one roller having a cylindrical shape, the roller being made of an electrically-conductive material and serving as a heating means; a roller support shaft supporting the roller pivotably about an axis of rotation of the cylindrical shape; a support supporting the roller support shaft and having an electrode electrically connected to the roller; and a cooling channel serving as an air channel for discharging cooling air to a contact surface between the part of the sheet metal to be repaired and the roller. The cooling channel is formed inside the roller support shaft and has a discharge port that discharges the cooling air to the contact surface between the part of the sheet metal to be repaired and the roller.

Abstract: An object to the invention is to narrow the region burned by the preheating current at the spot welding. Structure is provided for allowing conventional welding current to be flowed between a first welding electrode tip and a contact member intermittently via an electronic switch until a predetermined current starts to flow between a first welding electrode tip and a second welding electrode tip.

Abstract: Welding overlapped work pieces in electrical contact with each other, the exposed surface of the lower work piece having an insulating coating. The overlapped work pieces are interposed between opposed first and second electrodes, the second electrode bearing against said coating. Initial current flow to said first electrode activates a circuit which results in heating the work pieces to melt the coating under the second electrode, whereupon current flows between the electrodes to produce a spot weld. Detection means senses the flow of current between the electrodes and sends a signal to a switch to render inoperative the heating circuit. This reduces the heated region extending outwardly from the spot welding area to prevent deterioration in the strength of the welded work pieces because of a change in the quality of the metal. The apparatus also conserves power normally consumed for heating.

Abstract: A method for spot welding metal articles having coatings on the surfaces thereof in which the coating on the outer surface of one of the articles is removed by heating the article as a resistance in an electric circuit. This is done using low amperage current. When the coating is removed, the current can flow freely between the electrodes at high current to effect a secure weld without sparking, distortion or boring of the articles.