Patent GB-1291481-A (GB)
Title: Improvements in and relating to resistance welding of metal sheets provided with insulating layers
Inventor: BECKER OTTO ALFRED
IPC: B23K11/16
Filed: 1969-10-13
Abstract: 1291481 Welding by pressure D A BECKER 13 Oct 1969 [26 Oct 1968 7 Nov 1968 31 May 1969 3 Sept 1969 20 Sept 1969] 50199/69 Heading B3R In resistance welding two metal sheets together, each being covered with an insulating layer, a recess bounded by at least one edge of the metal is provided in a first surface of one sheet, the sheets are superimposed so that a metal area of the second sheet faces the recess and edge or edges of the first sheet and welding current is passed between the edge or edges and the metal area and through at least one of the sheets parallel to the surfaces of that sheet. The recess may be formed by a rotary cutting tool or by embossing. A sheet 1, Fig. 3, coated on both sides has the coating removed on the upper side at 1c and at the under side at 1c<SP>1</SP>, a cylindrical projection is provided in the sheet by means of a punch acting on the area 1c in co-operation with a die, and then a cavity 1e is formed in the projection by a part spherical milling cutter guided in a sleeve centred on the projection. The sharp annular edge 1e<SP>11</SP> is then engaged with a bared area 2c of a coated sheet 2 and current and pressure is supplied by an electrode 5 while the sheet 2 is connected to the other side of the supply. Some arcing may occur in the cavity 1e but the outer coating 2b on sheet 2 remains undamaged. In a modification only the under side of the upper sheet is bared and a cylindrical recess is milled by an end milling cutter in the punched projection to leave a ring for contact with the lower sheet. The milling cutter is guided in the die which has cooling passages therein. Both sheets are connected to a capacitor welding supply and a punch is used to provide the pressure for welding. Milling of a bared area by a milling cutter having an inner part spherical cutter 7c, Fig. 6, and a ring shaped cutter 7d may be effected to produce a recess 1g, Fig. 7, bounded by an annular edge 1g<SP>11</SP> and an annular groove 1g<SP>1</SP> before the punching is effected and this punching may be effected by the welding electrode. For seam welding a strip of coating is removed, punching is effected by elongated members and milling is effected by a disc miller which produces a rectangular channel between two further channels having bevelled sides. For sheets too thick to be punched as before a recess is milled in the upper surface of the upper sheet and in the lower surface of the same sheet a ring shaped welding area is provided by milling by a tool similar to that shown in Fig. 6, but with a flat end cutter instead of a part spherical cutter and after assembling with a lower sheet the electrode applied to the recess in the upper surface of the upper sheet deforms the milled region. In other constructions milling cutters having inner flat cutters surrounded by ring cutters are used to produce tapering projections on the lower surface of the upper sheets and welding to another sheet is effected using a capacitor supply and a ram to provide pressure. The tapered rings provide the formation of arcs. Similar tapered projections 1l<SP>11</SP>, Fig. 16, may be produced in thin sheets by embossing since milling is not possible. Instead of the recesses, edges and grooves being annular they may be elongated to provide for seam welding.