Effect of compaction process sequence on axial density distribution of green compacts

During powder compaction, frictional forces between the compact and the tool elements are developed. This causes pressure gradients in the compact, which produces, at the same time, undesirable density differences. This work presents a study about the effect of the compaction process sequence (CPS) and the ejection process on the axial density distribution during the uniaxial double ended pressing process of a high slenderness bushing. Different pressing processes were selected and carried out with a hydraulic press at laboratory and industrial levels (differences in the extraction method). Compacts were presintered and cut into thin discs in order to measure the local densities along the part, using the Archimedes' method. The obtained results show that the compaction process sequence has an important effect on the axial density distribution in a green compact, mainly in the case of compacts of high slenderness (>5). The ejection causes in the compact a post-compaction modification of the axial density distribution. Therefore, it is necessary to optimise the pressing process to obtain an adequate density distribution for each specific part.