Guo, Yu (2010)
Ph.D. thesis, University of Birmingham.
This thesis reports numerical analyses of powder flow, mixing and segregation behavior during die filling in a vacuum and in air using an Eulerian-Lagrangian model, which employs a Discrete Element Method (DEM) for the particles and Computational Fluid Dynamics (CFD) for the air with a two-way air-particle interaction coupling term. The effects of air and particle properties (size, density, size distribution, cohesion etc.) on powder flow are explored. The results are in a good agreement with experimental observations. Powder flow is characterized in terms of a dimensionless mass flow rate and a critical filling velocity. When air is present, the powder flow characteristics depend on the particle size and density and can be classified into an air-sensitive regime and an air-inert regime. It is found that the difference in particle size and/or density can cause segregation during die filling. Therefore, parametric studies are undertaken to examine the effects of some factors, such as particle size or density ratio, shoe speed, initial mass fraction of fine particles, initial height of powder bed and cohesion. Suction filling with a movable punch is also simulated. It has been shown that the utilization of suction can significantly improve the powder flow rate and reduce the density-induced segregation.
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