GB1276901A - A method of producing electrical contact elements - Google Patents

Abstract

1276901 Making electrical contacts; welding by pressure CHUGAI ELECTRIC INDUSTRIAL CO Ltd 11 June, 1969 [21 June, 1968; 2 Aug 1968] 29522/69 Headings B3A and B3R. In making an electrical contact element a metal member is contacted by a ductile contact metal, pressure is applied to cold deform the contact metal and partially reduce its thickness by at least 20% to bring the member and contact metal into intimate contact and the deformed contact metal is heated while under the applied pressure to a temperature above its recrystallization temperature but below its melting point to effect metallurgical bonding of the member and contact metal. The contact metal may be silver, platinum, gold, palladium or alloys based on these metals and the substrate metal may be iron, mild steel, low carbon steel, spring steel, stainless steel, copper and copper base alloys, e.g. copper-zinc, beryllium copper, copper-phosphorus, silver, silver base copper alloys, silver base alloys, aluminium, aluminium base alloys, nickel, or nickel silver. In one embodiment contact metal 1, Fig. 1, having a high cold bonding tendency, is placed on a substrate 2 of relatively poor cold bonding tendency and with the substrate supported on a water cooled die 5, a high-speed steel or cemented tungsten carbide punch 3 having a cavity 3A of a volume no greater than that of the metal 1 but of lesser height is brought down to deform the metal 1, e.g. to 50% reduction in height. When the increase in hardness due to the applied pressure resists further deformation a high current pulse, e.g. lasting for 200 millisecs. is applied across the punch and die to heat the contact metal above its recrystallization temperature but below its melting point when it flows still further and fills the cavity 3A completely. The contact metal 1 is then metallurgically bonded to the substrate 2. After the initial deformation the surfaces may be as close as four Angstrom units and cold pressure welding may occur. In one example the contact metal is silver and the substrate nickel silver, and in another silver-dispersed cadmium oxide and stainless steel. In another embodiment a piece 1, Fig. 6, of ductile contact metal wire with a freshly cut end face 1<SP>1</SP> is superposed on the freshly cut face 2<SP>1</SP> of a piece 2 of different ductile metal wire. The piece of wire 1 may be of silver, gold, platinum or alloys based on these metals or silver-cadmium oxide and the piece of wire 2 may be of silver, nickel, aluminium, iron or copper. The piece of wire 2 is mounted in a die 5 backed by a pin 4 and a punch 3 having a cavity 3A is lowered to deform the pieces 1, 2, a high current being immediately applied across the punch and die to heat both metals above their recrystallization temperature 1 when the pieces flow to fill the cavity 2A completely and form a rivet contact.