The influence of mold deflection on the prediction of packing pressure decay and part shrinkage

Injection Molding simulation traditionally considers the molding cavity to be a rigid fixed volume to be filled. However, disagreement is often observed between measured cavity pressures and predicted cavity pressures at the end of the packing phase. In this study, a coupled approach is implemented to include the effect of mold deflection in the flow simulation of the injection molding process including the packing phase. Through comparison to our database of molding experiments in instrumented molds, the significant impact of mold deflection on in-cavity packing pressure decay is demonstrated and improved simulation accuracy is achieved. A simple methodology for determining the degree of mold deflection of any mold is also proposed. This study will also demonstrate the impact of improved cavity pressure predictions on shrinkage predictions and provide comparison to measured shrinkages for a range of polymer materials, molding geometries and processing conditions.