Fast Numerical Algorithm for Optimization Mold Shape of Direct Injection Molding Process

Abstract

Accurately and rapidly predicting the shrink mold shape of direct injection-expanded foam molding is an important and difficult task. This molding method is widely used by sports shoe sole manufacturers to create shock-resistant materials. Modifying the shrink mold shape using the numerical optimization method is crucial to rapidly obtaining the correct shrink mold size. This study uses a series of rectangle specimens to identify the relationship between the thermal heating of molding and the expansion ratio of ethylene vinyl acetate foam material and then uses this thermal expansion ratio to simulate expansion behavior. The experiments in this study also use the actual shoe sole type, which has the original three-dimensional (3D) shape, and use the proposed simulation method to obtain the simulation expansion shape. This study also develops an optimization algorithm based on 3D registration and the Newton–Raphson method to obtain the shrink mold shape. We also manufactured the shrink mold and obtained the shoe sole product to compare any discrepancies between the product and the original 3D shape. The results of this method meet the requirements of the shoe sole factory (i.e., achieve a difference of less than 3 mm).

Keywords:

• Ethylene vinyl acetate (EVA)
• Expansion
• Molding
• Optimization
• Shoe