Patent GB-1272945-A (GB)
Title: Improvements in and relating to the welding or brazing of metal sheets coated with insulating layers
Inventor: BECKER OTTO ALFRED
IPC: B23K11/16
Filed: 1969-05-01
Abstract: 1,272,945. Welding by pressure; brazing. O. A. BECKER. 1 May, 1969 [8 May, 1968; 28 May, 1968; 19 Aug., 1968; 21 Aug., 1968; 3 Sept., 1968; 17 Sept., 1968; 19 Sept., 1968; 9 Oct., 1968; 26 Oct., 1968; 7 Nov., 1968; 14 Dec., 1968; 17 Jan., 1969], No. 22169/69. Heading B3R. In resistance welding or brazing two metal sheets coated at least on their outer surfaces with non-conducting material, the welding or brazing current is caused to flow through at least one of the metal sheets parallel to the surfaces thereof such that the outer coating of at least one sheet remains continuous. Two metal sheets 1, 2, Fig. 1, having non-metallic layers la, 1b, 2a, 2b, e.g. synthetic layers, phosphate layers or oxide layers are overlapped, the layer 2b of sheet 2 rests on a cooling plate supported on an electrode 6 via an insulator 12 and an electrode 5 engages a bared area 1c on the sheet 1. The sheets are connected by cables 7, 7a to the electrode 6 so that current flows through sheet 1 which becomes heated to melt the layers 1b, 2a allowing current to pass into the sheet 2 to effect a spot weld beneath the electrode 5. The layer 2b on the cooling plate 10 does not melt. In a modification both electrodes engage the bared area of the upper sheet, one being annular to surround the other, and a connection is made from the annular electrode to the lower sheet. For welding an upper sheet coated on both surfaces to a pair of side by side sheets also coated on both surfaces, the lower sheets rest on a cooling plate and the two electrodes are in contact with spaced bared areas of the upper sheet, connections in parallel with each electrode being made to the lower sheets. A spot weld between the upper sheet and each lower sheet is formed without melting the lowermost layer on the lower sheets. In another embodiment two sheets coated on both sides are arranged on a cooling plate with a wire between the sheet and a roller electrode engages an elongated bared area of the upper sheet. The current supply is connected to the roller on one side and to the sheets in parallel on the other side and heating melts the adjacent coatings on the sheets with the wire establishing contact between the sheets for seam welding. To effect welding without baring the upper sheet the wire is provided between the roller and the upper sheet and the two sheets are in contact. Current is supplied additionally to the wire so that heating of the wire melts the upper coating to allow current flow through the upper sheet and heating to melt the adjacent coatings and then seam welding. In order to allow welding without damaging either outer coating parallel wires 9a, Fig. 6, are provided between upper coated sheet 1 and lower coated sheet 2, cooling plates 10 with spring-pressed coolant ducts 19 are arranged in contact with the sheets 1, 2 and electromagnetic vibrators 13 engage the cooling plates. The current supply is connected to the two sheets and to the wires which became heated melt the adjacent coatings and allow welding between the sheets, vibration by devices 13 accelerating the process. In a modification a second series of wires cross the first wires or a metal sheet covers the first wires. The wires may each have a sharp edged cross-section instead of round. For welding coated walls, one edge is turned through 180 degrees and the other edge is arranged within the U so formed, discs, strips or wires being inserted between bared areas of the edges. To direct the welding current in the case of two coated sheets with a wire between bared areas, two plates forming a capacitor are provided one above and one below the sheets. The coatings may be the oxidized surfaces of light alloy sheets or the bonderized surfaces of steel sheets. Small bared zones 1c, 1d, Fig. 12, are provided on the upper sheet 1 and in the lower sheet an annular recess 2f is milled to leave an upstanding pin 2g. The sheets are pressed on to a cooling plate 10 by a ram 17 acting through a cooling plate 10 and the tungsten tip 5b of an electrode engages the bared area 1c. Both sheets may be milled as before, using an insert between the welding projections and without a bared outer zone. The milled recesses may be of rectangular section and contain a wire or sphere insert or of V- shaped section and contain a wire. The contacts to the ends of the sheet comprise flexible silver-plated copper strips backed by strips of rubber. A recess may be milled in the upper sheet and a dimple is produced below the recess, the electrode engaging the recess having a spring loaded pin to engage the reverse side of the dimple. The insert between two inner bared areas of the coated sheets may be of lower melting point than the sheets, e.g. of brazing solder for steel sheets or low melting aluminium alloy for aluminium sheets. Flux may be employed. With the adjacent coatings removed on each sheet and with a capacitor discharge supply connected across the sheets, arcs form between the bared areas before the areas are finally pressed together. The formation of the arcs are promoted by circular ribs or longitudinal ribs on the bared areas. Inserts having ribs or points may also be used as may be a pointed pin inserted through a bore in the upper member, arcs being established and the pin being fused. An upper coated sheet 1, Fig. 28, has a bared zone 1c, a bared zone 1d and a bore li and the lower sheet 2 has a bared zone 2c. An electrode 5 connected to one side of a capacitor pulse supply K presses a pin 52 having  a pointed bottom against the lower sheet, arcs  being established between the pin and the sheets, the pin being fused and forced into the space between the sheets. To weld aluminium, brass or copper sheets coated on the outer surface only an insert of paper or synthetic material is provided between the sheets with lengths of steel wire in cut-outs in the paper &c. insert. Arcs are established by the wire lengths which became welded to the sheets. An insert piece (75), Fig. 33 (not shown), with a lower projection (75g) is held by vacuum or magnetically in an electrode (5) held raised by a solenoid coil and when current is supplied to the electrode and lower sheet the solenoid is de-energized and the insert is thrust against the lower sheet. An upper sheet with a milled lower projection is then thrust against the welded on insert to weld thereto. A headed welding pin may be thrust through an aperture in the upper sheet to initiate an arc with the lower sheet, the head of the pin bearing like a rivet on the upper sheet. Steel sheets may be welded to brass or copper or aluminium sheets or brass sheet may be welded to copper sheets. When welding an upper sheet having a milled downward projection to a lower sheet adhesively joined to another coated sheet capacitor members are arranged above and below the assembly with a capacitor foil between the upper and lower sheets. Preheating of an upper sheet may be effected prior to capacitor discharge welding and the upper electrode may be arranged in a vacuum chamber or may be pressurized by an electromagnet. A pin 131, Fig. 39, is welded to an upper sheet 1, the pin is held in a stud welding too, a ring 132 of high melting material is provided between the upper sheet 1 and lower sheet 2, the pin is lifted by the tool to initiate an arc between the projection 1k on the upper sheet and the bared area on the lower sheet and then the projection is pressed against the lower sheet. The pin is then broken off at notches 131a.