An analysis of the stress state in a green part during ejection from the die

The prediction of ejection cracks in green parts through simulation requires a constitutive model for the powder and an accurate analysis of the stress state in critical regions. We analyse this latter aspect by conducting detailed finite element simulations of the ejection of an axisymmetric part from the die. The compaction phase is simulated using the Drucker-Prager Cap model as a prototype constitutive law. Qualitative features of the stress state in the relevant regions are characterised and the influence of friction and an induced elastic anisotropy is analysed. The results are believed to aid establishing an appropriate 'failure criterion' for green parts.