The effects of wall friction in powder compaction

This paper investigates some of the effects of the powder-die-wall friction that arise during the compaction of ceramic powders in rigid moulds. Results obtained from experimental, analytical and numerical studies of the cylindrical die compaction of an agglomerated alumina powder are reported. The density distributions within various powder compacts are determined experimentally using a coloured layer technique and the effects of the state of the die-wall lubrication, the compact aspect ratio and the ultimate applied compaction stress are studied. The density distribution and wall stresses are also determined analytically using a first order semi-empirical differential slice model. The influence of the variation in the powder-die-wall friction coefficient with the state of the die-wall lubrication and the applied load is investigated experimentally by measuring the stress transmission generated in the die compaction process. These data, combined with an established wall friction model, which is used to describe the powder-die-wall boundary conditions, are adopted as input parameters for a numerical finite element model of powder compaction which incorporates a non-linear elastic constitutive material model. The numerical results generated provide a quantitative prediction of the stresses and, hence, of the density distributions created, and show some agreement with the experimentally determined distributions and those obtained from the application of the first-order analytical model. (C) 1998 Elsevier Science B.V.