Cold compaction of composite powders

Powder compaction is a production method commonly used in the manufacturing industry today. In order to minimize costly experiments and to optimize serial production of details several methods to analyze the powder compaction process are developed and used. One method is to use micromechanical analysis where the local description of contact between two individual particles is of great importance. In this dissertation a visco-plastic contact law has been used and further developed in order to understand the powder compaction process at packing, low relative density compaction up to high relative density compaction. In order to relax some assumptions from previous theoretical studies simulation with the discrete element method (DEM) was performed. Up to 10.000 spherical particles were used in packing and early compaction simulation. It was found that rearrangement of particles is one of the major densification mechanisms in the early phases of compaction. At die compaction this effect of rearrangement was shown to be more pronounced than predicted from theoretical analyses. It was also found that the size ratio of particles is of importance when the number fraction of small particles in the compound is high. The finite element method has been used for numerical analyses to investigate the local contact problem between two particles when self-similarity no longer prevail. Based on the numerical results a suggestion for an approximate compliance relation was made. With this approximate formula the local compliance behaviour between two dissimilar particles was analysed. These findings are directly applicable to simulations with the discrete element method. Finally, an investigation using the finite element method to evaluate the range of the accuracy for theoretical and approximate compliance formula has been done with compounds of different regular lattices. It was found that the range of accuracy is much dependent on the number of contacts within the lattices, specially new forming contacts during the compaction.QC 20101007