Patent GB-1388444-A (GB)
Title: Magnetic pulse welding and apparatus therefor
IPC: B23K13/04
Filed: 1972-06-09
Abstract: 1388444 Welding by pressure; shearing; upsetting; cutting by fusion; electromagnetic forming; bending and corrugating metal THERMATOOL CORP 9 June 1972 [2 July 1971] 27203/72 Headings B3E B3H B3Q B3R B3V and B3W In forge welding a pair of portions of electrically conductive material, one portion is placed adjacent the other, a continuous conductive electrical circuit is established including a first current path through at least one of the portions and a second current path disposed closing adjacent but spaced from the one portion, a source of pulsed current is connected to the circuit to cause one or more pulses of current to flow in a first direction in the first path and in an opposite direction in the second path and one or more current pulses are provided to produce interacting magnetic fields which urge one portion towards the other. In an embodiment two metal sheets 10, 11, Fig. 1, are welded by support bars 13 with their edges overlapping and in contact on a copper anvil 12. A conductor 15 is arranged above the sheets with one end connected to one end of the anvil and the other connected to one side of an electric circuit, another conductor 14 being connected to the other end of the anvil and to the other side of the circuit. In operation the conductors 14, 15 are connected initially to a source of high frequency current 27, e.g. 3-450KH so that current flows in both overlapped edges to heat them to a welding condition and then the conductors are connected instead to a charged capacitor 20 which provides a large pulse producing interacting magnetic fields exerting downward pressure on the sheets against the anvil. A backing member preferably non-magnetic, to resist upward pressure on the conductor 15 is provided, secured to the anvil. The initial high frequency heating may be amitted when cold forge welding is effected. In a modification instead of using an anvil, a lower conductor, similar to the conductor 15, and spaced beneath the overlapped edges is provided, the two conductors being connected at one end to a jumper bar and two conductive bars each in contact with a sheet being also connected to the jumper bar. The circuit providing the high frequency current and the condenser pulse current is connected at one side to the conductive bars in parallel and at the other side to the conductors also in parallel to firstly heat the overlapped edges and then produce forging pressures from above and below the edges. The edges in this case may be spaced apart. In an embodiment in which the sheet 10, 11, Fig. 12, have upturned edges to be welded the sheets are arranged on an anvil 12 and two conductors 15f, 15g are arranged one on each side of the upturned edges. Conductor blocks 61, 62 connect the conductors in parallel and the anvil and block 61 are connected to a circuit as in Fig. 1. In a further embodiment sheets are arranged in butting relation over a recess in an anvil similar to that of Fig. 1 and the interacting magnetic fields produce a dent in the abutting edges. Twin conductors, one above and one below the abutting edges may be used instead when two dents are produced to effect forge welding. The portions being welded may be the end portions of a single sheet formed into a can body or pipe. The following subject matter not falling within the ambit of the invention is also described. A depression is formed in a metal sheet 10<SP>1</SP>, Fig. 3, by locating the sheet over an anvil 12<SP>1</SP> having an elongated cavity 36 and, preferably after heating the sheet by supplying high frequency current from the source 37, a current pulse is supplied from the source 20 to effect magnetic pulse forming of the sheet. The cavity may be wider than is shown or two parallel cavities may be employed. The cavity may be curved, discontinuous, contain angles and bends or may comprise a pattern. Alternatively a projection rather than a cavity may be used. Each part 12a, 12b, Fig. 9, of a two part anvil is provided with a hardened knife edge 40a, 40b across which edges a sheet 10<SP>1</SP> is laid. The conductors 14, 15 may be connected to a high frequency heating current source if preheating of the sheet is desired or only to a condenser impulse circuit. The condenser is discharged to produce a magnetic pressure pulse which causes a narrow strip to be cut from the sheet. The knife edges may be shaped so that the severed sheet edges include notches or tabs. In a modification a single knife edge on an anvil is provided when the sheet is simply cut in two. A plate 10 may be placed on a flat anvil 12, Fig. 20, and after preferably heating the plate beneath the conductor 15 to a molten condition at least partially through its thickness a current pulse produces a magnetic force which severs the plate. The arrangement may be such that the plate is only indented. The end of a sheet may be laid to extend beyond the edge of the anvil with the upper conductor above the sheet end and the magnetic force bends the sheet end down over the anvil. The conductor 15, Fig. 24, may extend beyond the sheet end when the magnetic force upsets the sheet at 76, the sheet possibly being preheated.