Simulations of Heat Transfer in Thermoplastic Injection Molds Manufactured by Additive Techniques

Abstract

AbstractThe cost and quality of complex thermoplastic parts manufactured by injection are traditionally limited by the design constraints on the mold cooling system. A possible way to overcome this problem is to produce the mold by additive manufacturing, which makes it possible to freely design the shape and position of the cooling channels. Such molds can have hollow spaces in order to reduce the manufacturing time by Selective Laser Melting and the use of costly materials. The complex geometry resulting from optimized cooling channels and hollow regions makes the prediction of the cooling system performance difficult. This work aims to devise a numerical methodology for the simulation of heat transfer phenomena between the polymer, the mold and the cooling channels. An Immersed Volume approach is chosen, where the different parts of the domain (i.e. the polymer, the cooling channels, the hollow regions and the mold) are represented implicitly and the thermo-mechanical properties of the materials vary smoothly at the interface between the parts. The energy and momentum equations are solved by a stabilized Finite Element method. In order to accurately resolve the large variations of material properties and the steep temperature gradients at interfaces, state-of-the art anisotropic mesh refinement techniques are employed. In a first step, we perform thermal calculations only. We then consider the proper thermo-mechanical coupling in the packing stage, as well as the ejection stage and the thermal contact resistance between the polymer part and the mold, in order to weight their influence on the part and the mold temperatures. The modeling strategy is first validated on a simple geometry of a center-gated disk and compared with experimental measurements. The agreement between the experimental results and the simulation is good. Simulations are then performed on an industrial case which illustrates the ability of the method to deal with complex geometries.