Bulk Density Reduction of Injection Molded Thermoplastic Foams via a Mold Design Approach

This study investigates the inter-relationships amongst processing parameters and mold design and their effects on relative density of injection molded foams. The limitation in lowering the overall bulk density of polymeric foams is one of the main drawbacks in injection foaming process. A sheet mold with a rectangular cavity was designed and manufactured which, includes an overflow channel connected with the main cavity via a secondary gate, the size of which was varied in this research. The effects of three parameters including chemical blowing agent weight percentage, gate width, and part thickness on reduction of relative density were investigated. Full factorial test experiments were applied in this research work. The results were used to determine the optimum conditions in terms of low foam bulk density and high cell density. The results showed that enhanced cell structure can be achieved at a larger part thickness and adjusting the secondary gate to an optimum thickness. The conclusions revealed that part thickness and secondary gate width were the most influential factors on reduction of relative density and part weight.