Determination of optimal parting directions in plastic injection mold design

Automatic recognition and extraction of undercut features is a bottleneck in computer-aided injection mold design. The number of undercuts and their locations affect the parting directions and surfaces, side-core mechanism, sliders and lifters design, and the overall structure of a mold. In this paper, a methodology is proposed for the recognition and extraction of undercuts based on their geometrical characteristics and topological relationships of the molded parts. With the developed software, undercuts can be classified and recognized automatically from a 3-D model of a molded part. In order to define the undercut criteria clearly, a new classification method is presented. Since most of the injection molded parts consist of curved surfaces and free-formed surfaces, recognition and extraction of these surfaces are also introduced. After all the undercuts are extracted, the optimal parting direction is chosen based on the proposed criterion of considering the number of possible undercuts and their corresponding undercut volumes. From the case studies on several industrial parts, the methodology developed is found to be efficient in determining the optimal parting direction of injection molded parts.