Lode dependency in the cold die powder compaction process

The powder forming industry looks to produce parts of increasing geometrical complexity as it is seen as a very efficient production process. This offers new challenges as three-dimensional states of stress are induced. In particular, granular and porous materials respond very differently to tensile and compressive stresses. Since experiments conducted in the 1990s, little exploration of the Lode dependency of powders was carried out. The present work investigates the effect of Lode dependency through numerical simulation, aiming to establish whether it affects the outcome of a compaction cycle and whether further experimental study of the phenomenon may be justified. To this effect, a Lode dependent model was developed and implemented in a finite element code, then two case studies were carried out. The results show that there is little impact on the density contours within the components and the stress levels during the compaction. As the parts are ejected from the die, surface stress levels are affected and this is of great interest when studying the onset of defects in powder compacts.

Lode dependent powder models reflect the mechanical weakness of granular material under tensile stresses, giving a more accurate insight into their behaviour under a wide range of conditions.Figure optionsDownload as PowerPoint slide