Runner Design with Minimum Volume for Multicavity Injection Molds: Part II. Runner Layout

Abstract

Following the optimal runner sizing given in Part I, this paper establishes rules for runner layouts to minimize volume using a mathematical analysis. For four cavities with their centers forming a rectangle, the X layout gives the smallest runner volume unless the aspect ratio of the rectangle exceeds 1.305. In the latter case, a double Y shaped (>-<) layout is the optimal. This rule is extended to multiple-of-four cavities in a rectangle and circularly arranged cavities. Several examples of optimal and recommended simpler runner layouts illustrate that runner volume can be reduced by up to 39%. In addition, a procedure based on a "runner design invariant" concept has been developed for modifying an existing runner design to reduce runner volume without knowing the material and processing parameters other than the power-law index.