The PVT effect on the final sintered dimensions of powder injection molded components

Accurate linear-shrinkage prediction of powder injection molded (PIM) components for tool scale-up is commonly achieved by a combination of estimating sintering shrinkage and prototyping. Sintering shrinkage calculations for mold scale-up can underestimate the final sintered shrinkage by up to 2%. This can be corrected by considering the pressure–volume–temperature (PVT) behavior during injection molding of a PIM feedstock. The molding shrinkage can be estimated from the PVT behavior of the molten powder/binder feedstock. In this effort, the PVT data of a PIM feedstock are related to processing parameters to predict the green shrinkage of PIM components. This is compared to experimental data on green and sintered component dimensions to develop a more accurate prediction of linear shrinkage. A relationship between injection molding process parameters, green component shrinkage, and sintering shrinkage is presented based on the PVT and sintering behavior of the PIM feedstock. A modified equation for improving linear shrinkage prediction is derived and presented. Experimental shrinkage results are within 1.1% error (0.2% difference) of the derived equation.