Improved tolerances by optimized powder mixes

Abstract

Dimensional stability is a prerequisite to produce net-shape P/M components. Improved dimensional stability will make the P/M route even more cost competitive compared to competing manufacturing techniques. Diffusion bonded powders and chemically bonded mixes are means to reduce dimensional scatter due to segregation of alloying elements. By utilizing specific bonding substances chemically bonded mixes exhibit superior flow properties that facilitate even filling of the die cavity in the press. In this presentation results are presented from a study comprising different mix compositions, type of alloying additives and use of bonded mixes, pointing out ways to improve dimensional stability. Introduction By bonding the alloying elements, segregation can be minimized. A common method for metallic elements such as copper, nickel and molybdenum is diffusion bonding to the iron powder particles [1, 2]. Organic binders are in general used to bond the graphite in order to minimize scatter in carbon content, but also to minimize dusting of the mixes [3]. All handling of powders may cause segregation of alloying elements. Segregation can take place on a macro scale resulting in variations from part to part but also within a component, which can result in dimensional distortion of the component. The type of alloying element has a significant impact on how prone the alloying elements in a mix are to segregate. Difference in size, density and morphology are driving forces for segregation [4].