Development Of A Silicone Mold Tool For Injection Molding Plastic Parts

Abstract

Injection molding is one of the most popular processing methods for manufacturing plastic parts. Typically, injection mold tools are made out of metal. The design and development of these metallic mold tools is a very expensive and lengthy process which means that it is difficult to incorporate this process into the prototyping stage of a product. Currently, the most widely researched method used for rapid prototyping of injection mold tools is additive manufacturing (AM). This project investigates an alternative to AM as a rapid prototyping method by investigating a cost-effective mold tool made out of silicone. A robust step by step process of creating a silicone mold tool is presented. To determine the right plastic to inject into the silicone mold tool, an injection molding simulation is conducted comparing three types of plastics and their effect on the filling of the mold tool. Following the simulation, Design of Experiment (DOE) is used to measure the main and interaction effects of the silicone mold tool’s durometer hardness, geometry, and design complexity on its performance. Additional DOE studies were conducted to optimize the injection molding processing parameters for fabricating ASTM D638 Type IV tensile specimens. From the experiments, it was found that a durometer of Shore A Hardness 40 is the most optimum value for a silicone mold tool. Durometers smaller than that increase the likelihood of failure by flash and durometers larger than that damage the mold tool through brittle failure. Design changes were made to the mold tool geometry to use 3D printed inserts and shorten the length of the runner, the latter of which resulted in ideal samples without any failures. Comparison of mechanical properties of the silicone mold test coupons with those produced using a metallic mold tool revealed that there was a 7.3% decrease in Ultimate Tensile Strength when going from metal to silicone mold tool, better than those previously reported for some AM mold tools. In conclusion, the silicone mold tool is a promising alternative to AM mold tools for rapid prototyping of injection molded parts with certain limitations.