Abstract
The powder injection molding (PIM) process is a cost efficient and important net-shape manufacturing process that is not completely understood. For the application of simulation programs for the powder injection molding process, apart from suitable physical models, exact material data and in particular knowledge of the flow behavior are essential in order to get precise numerical results. In this work, the flow behavior of a 316L stainless steel feedstock for powder injection molding was investigated. Additionally, the influence of pre-shearing on the flow behavior of PIM-feedstocks under practical conditions was examined and evaluated by a special PIM injection molding machine rheometer. In order to have a better understanding of key factors of PIM during the injection step, 3D non-isothermal numerical simulations were conducted with a commercial injection molding simulation software using experimental feedstock properties. The simulation results were compared with the experimental results. The mold filling studies amply illustrate the effect of mold temperature on the filling behavior during the mold filling stage. Moreover, the rheological measurements showed that at low shear rates no zero shear viscosity was observed, but instead the viscosity further increased strongly. This flow behavior could be described with the Cross-WLF approach with Herschel-Bulkley extension very well.
Highlights
Introduction zero viscosityPowder injection molding (PIM) is s a multi-step technology for manufacturing complex metal or ceramic parts
In this paper we present some experimental techniques to determine the rheological behavior of powder injection molding (PIM)-feedstock
For 316LA whose particle size distribution is bimodal, a change in flow characteristic was observed during the viscosity measurement on the high pressure capillary rheometer with the slit die
Summary
Powder injection molding (PIM) is s a multi-step technology for manufacturing complex metal or ceramic parts. It consists of four sequential technological steps – mixing, injection molding, debinding and sintering. In contrast to unfilled thermoplastics for PIM-feedstocks no Newtonian plateau is observed at very low shear rates, but instead the viscosity keeps increasing strongly. This indicates the possible presence of the limiting shear stress (flow limit) known as yield stress or yield point, depending on the material structure and the applied shear stress
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