Finite element simulation of cold isostatic pressing and sintering of SiC components

Finite element simulations were performed for cold isostatic pressing of SiC powder. To describe the compaction behaviour, the Drucker-Prager-Cap model implemented in ABAQUS/Explicit® computer program was applied. The influence of friction between powder and steel core as well as rubber bag on the density distribution was investigated for compacts with cylindrical and helical cores. Simulations with and without rubber bags were made showing that the effect of the bag on the density distribution is fairly small, at least for thin bags. Due to the presence of the steel core, density gradients develop during compaction, although the outer pressure is hydrostatic. The predicted density variation is consistent with experimental results. After the pressing cycle it may be difficult to remove the helical steel core from the powder compact. The simulation shows that the elastic spring-back leads to residual stresses which may reach the green strength of the powder compact, so that the part may crack during the unloading or removal of the helical core. Investigations of the sintering behaviour predict small shape distortions due to the slightly inhomogeneous density distribution of the green body. However, the differences between the ideal geometry and the predicted outline after sintering are small.