Runner Design with Minimum Volume for Multicavity Injection Molds: Part I. Runner Sizing

Abstract

A design procedure has been developed which guarantees the minimum volume for a balanced runner system filling an injection mold with identical cavities. The procedure is based on a mathematically rigorous derivation for the power-law model under conditions where viscosity is not significantly altered by temperature variations. The design rule for runner sizing to minimize volume is unexpectedly simple: The diameter of any runner downstream from ajunction is determined by dividing the diameter of the upstream runner by the cube root of the number of downstream branches at thejunction. This applies to any runner length, number of branches, power-law index, and location within the runner system. The rule has been extended to noncircular runners.