Influence of Particle Size on the Phenomena Responsible for Densification during Uniaxial Cold Compaction

In this work the behaviour of austenitic stainless steel powder during uniaxial cold compaction was investigated; experiments were carried out in a hydraulic press, using powder mixtures with different particle size distribution. The powders were compacted to the same green density; moreover, compaction tests at intermediate forces were carried out, and the data continuously recorded by the press in terms of force and displacement of the axes were analysed, allowing to distinguish the contribution of the reversible phenomena (elastic deformation of powders and tools) and of the irreversible phenomena (rearrangement and plastic deformation of the powders). An analytical model describing the trend of reversible and irreversible displacements versus the applied force was proposed. The influence of particle size on the resistance to rearrangement, elastic deformation and plastic deformation was therefore experimentally determined. Different H/D ratios were considered in order to account for the influence of geometry too. The results are implemented into a knowledge base data, to be used as a design tool for PM structural parts.