Harris, A., Lee, E., Peraro, W., Nunes, S. et al., "Automotive Interior Injection Molded Parts Using Microcellular Foaming Technology," SAE Technical Paper 2014-36-0172, 2014, doi:10.4271/2014-36-0172.
The microcellular foam injection molding process for thermoplastic materials provides design flexibility and cost savings opportunities not found in conventional injection molding. This process allows for plastic part design with material wall thickness optimized for functionality.The combination of density reduction and design for functionality can result in material and weight savings of up to 20%. With the correct equipment configuration, mold design, and processing conditions, these microcellular voids are uniform in size and distribution. The use of microcellular foam molding provides significant reductions in cycle time, material consumption, injection pressure, and clamp tonnage.In this work, a physical foam molding process, MuCell, is applied to a polypropylene (PP) composite. The MuCell injection molding process involves the highly controlled use of gas in supercritical state, as the physical blowing agent, to create millions of micron-sized voids in thin wall molded parts (less than 3mm).The results show that a weight reduction can be achieved without significant degradation in mechanical properties, such as stiffness and impact resistance. MuCell also contributes to faster cooling from the melt as well as the elimination of pack and hold phase, which both result in shorter injection molding cycle times and reduced warpage.Once material tests have been completed, final part tests will also be performed, to validate established design specifications. These results presented here indicate that microcellular foam molding technology has good potential to be applied to interior parts of vehicles, contributing to weight reduction and productivity increase.