POWDER-METALLURGY MAIN BEARING CAPS FOR AUTOMOTIVE ENGINES

Powder metallurgy main bearing caps (MBC) are being used for the first time in General Motors (GM) 3100 and 3800 V6 engines in 1993. This pr oduct will consume over 5000 tons of powder a year making it the bigge st volume application for P/M in North America. P/M was chosen to repl ace the traditional material, cast iron, because of its functional adv antages and because its net shape capability eliminated major investme nts in MBC machining lines at GM. A high strength low cost P/M alloy s teel was developed for this application, since grey cast iron was not strong enough and ductile cast iron was both expensive and difficult t o machine. The paper explains the functional requirements of an MBC. T he cast iron and P/M materials and processes are compared and the desi gn benefits of P/M are described. In addition, the PIM MBC requirement s of strength, consistency, integrity (freedom from defects) and machi nability are discussed, including the various experiments and verifica tion tests.