Imbalance filling of multi-cavity tooling during powder injection molding

A shortened cycle time with improved productivity is a key justification for multi-cavity molds. However, filling imbalance is an offsetting barrier for multi-cavity molds. The sources for an imbalance are often subtle, in both conventional plastic injection molding and powder injection molding (PIM) industries. The greater thermal conductivity of the PIM feedstock and the subsequent large sintering shrinkage amplify the issue for PIM. Due to its characteristic, the size of PIM parts is relatively smaller than the conventional plastic injection molding and so multi-cavity molds are widely used. Despite the geometrically systematic delivery system and cavities, asymmetric branching of flow paths, uneven viscous heating, and cooling variations exist for the molten feedstock flow to the cavities. These variations significantly limit the benefit of a multi-cavity mold. We investigated the imbalance filling between the near- and far-side cavities in a geometrically symmetric multi-cavity mold for PIM. Via molding simulations and experiments we found that imbalanced filling arises from subtle factors such as non-uniform mold cooling, uneven conduction of the molten feedstock into mold, and uneven viscous heating and their competitive roles between conduction/convection and viscous heating in the multi-cavity molds mainly contribute to imbalance filling the same way in the conventional plastic injection molding.