GB973220A - Method of and apparatus for resistance welding - Google Patents

Abstract

973,220. Welding by pressure. F. FRUNGEL. Jan. 31, 1961, No. 3600/61. Heading B3R. In resistance welding a member to one face of a workpiece, the member is contacted by one electrode and the one face is contacted by another electrode having an annular contact area about the member and larger than that of the member and current is supplied to the electrodes to weld the member to the workpiece without producing heat to damage the opposite face of the workpiece. Apparatus for welding the member using a current impulse of short duration, comprises an inner electrode adapted to hold the member and surrounded telescopically by a hollow outer electrode having a contact face to engage the workpiece, means for pressing the outer electrode against the workpiece, and the inner electrode and the member held thereby against the workpiece and conductor means connected to the inner and outer electrodes, the total inductance of the conductors and electrodes being less than 0.1 microhenries A bolt 3, Fig. 1, to be welded to one face of a thin metal sheet 1 coated on its other face with synthetic insulating material has a projecting rim and is held in a cylindrical inner electrode 5 telescopically surrounded by a tubular electrode 10 which engages the sheet. Current from an impulse transformer is conducted to the electrodes by strips 6, 9 and elastic insulating material 12 is arranged between the conductors with similar material 7, 12a above the strip 6 to transmit mechanical pressure to the electrode from heads 8, 8a. In a modification for welding a shaft or pin 16, Fig. 2, having a projecting rim 16 to the uncoated side of a coated sheet metal cup la, the inner electrode comprises a tapered split chuck 14 engaged in a tapered recess 5a in a flanged body 5b, an elastic pad 7a being provided between the end of the pin and the chuck. A pressure head 8b is secured to the flanged body 5b with conductor 6 between them and an elastic ring 12 is provided between the flange of body 5b and the insulated outer electrode 10a. The pressure exerted by the head 8a firstly causes the body 5b to clamp the chuck on to the pin 16. The current impulse which may be of less than 10, e.g. 1 milliseconds duration, causes welding of the members at the region of the projections 4 without producing a temperature of e.g. 100‹ C. sufficient to damage the coating on the sheet metal. The workpiece may be polished on one side rather than coated and may be of aluminium and the electrodes may be square or rectangular section tubes. A thick copper plate or a water cooled rubber bag may be provided adjacent the coated or polished surface. The impulse may be from a condenser discharge direct or transformed or from lowfrequency A.C. or a battery source and the mechanical pressure may increase with increase of current.