Numerical simulation of die pressing and sintering-development of constitutive equations

Micromechanical models for the pressing and sintering of powders are described and macroscopic constitutive equations are derived from them. The effects of cohesion and friction between powder particles on the macroscopic behaviour during compaction are explored. The micromechanical model for sintering is based on the assumption that the surface of the open pore space is in equilibrium and that densification and creep occur by grain boundary diffusion. The so developed constitutive equations are implemented in finite element codes. A simple example is shown, in which the pressing and sintering of a hard-metal cutting tool with wedge-type profile is simulated. The simulation correctly predicts large gradients in green density and, as a consequence, large shape distortions during sintering.