Patent GB-1277579-A (GB)
Title: Pistons
Inventor: HILL HAROLD TAYLOR
IPC: F16J1/00
Filed: 1968-07-15
Abstract: 1277579 Making pistons; welding by pressure WELLWORTHY Ltd 3 July 1969 [15 July 1968 21 Nov 1968] 33714/68 and 55290/68 Headings B3A and B3R A piston having a hollow light metal body part incorporating a piston crown includes two parts friction welded together. A body 10, Fig. 1, of aluminium alloy or magnesium alloy is cast or forged and machined and a ring carrier 11 of steel, stainless steel, bronze, hypereutectic aluminium-silicon alloy or other wear resistant metal is machined to fit a recess in the body and the body 10 and carrier 11 held in chucks are relatively rotated unidirectionally for say 3 sees. and pressed together. Melting of the contacting surfaces occurs, rotation is stopped and the parts are held in contact to cool to form a welded joint 13. After cleaning by machining a top land ring 12 e.g. of the same material as the body 10 or of cast aluminium alloy if the body is of forged aluminium alloy, is similarly friction welded at 14 to the carrier 11 and body 10. Machining to form piston ring grooves is then effected. Rubbing need not take place between the circumferential surfaces but when welding a ferrous carrier 11 to an aluminium alloy body frusto-conical co-operating surfaces may be provided. A shaped ring or rings may be friction welded to the body to provide an annular cavity therebetween. To provide a crown part of different material from the remainder of the body, the latter is formed with a frusto-conical recess in its upper face in which an insert is friction welded to leave a cavity, the insert being of thermal shock resistant material e.g. aluminium-copper-nickel-manganese alloy, sintered aluminium, copper alloy, nickel alloy or steel and having a combustion bowl subsequently machined therein. A body part 50, Fig. 5, with an annular recess 51 and a recess 52 in its upper surface is friction welded to a crown part 53 formed with matching recesses and e.g. of the above thermal shock resistant material, the central recess 52 allowing for outflow of weld metal and possibly for receiving cooling liquid when it would be connected to the annular cavity by radial passages. A piston with a combustion bowl in the crown may have a bowl lip of heat resisting material e.g. austenitic steel or nickel or chromium base alloy friction welded thereto and a similar lip may be provided for a cavity machined in an insert friction welded in the body. An insert offset from the piston axis may be friction welded to the body to provide a hot spot and a bushing e.g. of bronze may be friction welded in the aluminium or magnesium alloy gudgeon pin boss. The parts to be welded may be provided with chuck holding lugs which are subsequently machined off. The mating surface of at least one part may be cleaned by immersion in hot caustic soda and washing in nitric acid and the mating surface of at least one part, which may or may not be cleaned, may be coated with a metal or alloy such as nickel, copper, silver, gold, iron, chromium, molybdenum, tungsten or tin, lead, zinc, cadmium or antimony. The coating may be applied by electro deposition, immersion plating or spraying or from the vapour phase. The parts to be friction welded may be preheated by an induction coil.