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Numerical simulation of porosity of cohesive powders after die filling process in dependence of different pouring and shaking recipes

  • : Daniel Schiochet Nasato1, Stefan Pirker1, Christoph Kloss2, Thomas Lichtenegger1
  • : 1Johannes Kepler University - Department of Particulate Flow Mode, 2DCS Computing GmbH
  • : PDF Download
  • : 2015

Abstract

Powder compaction and sintering are important techniques for the mass production of geometrically complex parts. In general, a consistent and uniform die filling process is always desirable. Heterogeneity during die filling can propagate through the subsequent processes and finally lead to serious product defects, such as cracking, low strength, distortion and shrinkage.

We propose an approach using discrete element method (DEM) simulation to study the die filling process with and without internals using cohesive and non-cohesive powder. Special care has to be taken to correctly include the effect of cohesion when using coarse grained DEM particles. We subsequently combined DEM with a Monte Carlo approach to calculate local porosity and investigated the porosity distribution in dependence on different pouring recipes as well as on cohesion and particle size effects. This methodology allows us to identify porosity defects especially in complex die configurations.

Simulations revealed that cohesion strongly affects the porosity distribution. In case of cohesive powders we observe significantly larger porosities near internal and external walls. This agrees well with experimental evidence through observation of a stable cake formed of very cohesive Molybdenum (Mo) powder.

Finally, these simulations represent a versatile tool for studying concepts of consolidating the powder inventory inside the die by compaction, shaking, knocking or centrifuging.

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