Experimental and numerical investigations of powder transfer

In this paper, we examine the powder transfer process, a typical stage in the manufacture of multi-levelled components in the powder metallurgy (PM) industry. Both experimental and numerical studies of powder transfer are presented. Experiments have been conducted using a stepped die with a glass front face, which allows the die-filling and powder transfer processes to be observed using a high-speed video system. A numerical model based on the discrete element method (DEM) has been developed, in which particles of irregular shape are considered. The influence of powder characteristics and particle-to-die size ratio on the powder transfer process have been investigated. It is found that a depression at the top of the die cavity is a typical feature, and the degree of the depression depends on powder characteristics (such as morphology and average particle size) and the inter-particle friction coefficient. The depression increases as the irregularity of the powder morphology, the average particle size and the inter-particle friction increase. It is also demonstrated that the shear zone created during transfer has a lower relative density. The capability of discrete element simulations to capture the major features of the powder transfer process has been demonstrated. Both beneficial and detrimental effects of this process are addressed. The combination of experimental and numerical studies provides new insights, which enhance our understanding of the mechanism of powder transfer.