Influence of Fill Imbalance on Pressure Drop in Injection Molding

Abstract

During injection molding process melted polymer is introduced into mold cavity due to the pressure delivered from injection unit. Mold design principles suggests that filling of the cavity should be balanced. It means that the furthest regions of cavity (measured from injection point) should be filled at the same time to avoid problems with differential shrinkage and injection pressure drop. Fill imbalance can lead to the significant increase of pressure drop and needed clamp force, that can be compensated with more powereful injection molding machines. In this paper the relation between fill imbalance and injection pressure needed for cavity filling were investigated with Autodesk Moldflow Insight software. In this research several different shapes with thickness change of analyzed parts were performed to measure the significance of imbalance on injection pressure drop. It was found that it is possible to find a gate location even for geometrically imbalanced part, where significant pressure drop reduction can be obtained. Additionally, It was found that lowering V/P switchover point can provide significant reduction of needed injection pressure even if gate location must be placed in unfavorable location