Combining foam injection molding with batch foaming to improve cell density and control cellular orientation via multiple gas dissolution and desorption processes

In contrast to solid parts fabricated through conventional injection molding (CIM), foamed parts manufactured via foam injection molding (FIM) exhibit substantial variations in mechanical properties, which are attributed to differences in the cellular structure. In this study, parts with different cellular structures are fabricated via FIM, during which the gas dissolution and desorption processes are controlled by subjecting the gas-laden melt to reciprocating compression and expansion operations. The results suggest that the cell density can be drastically improved by rapidly decreasing the pressure caused by the mold opening and that the cell orientation obviously occurs in the direction perpendicular to the mold-opening direction. Moreover, the cell density and cellular orientation can be adjusted by utilizing appropriate mold opening and closing operations, leading to improvements in the resultant ultimate mechanical properties. In particular, the foamed samples fabricated with controlled mold opening-closing operations exhibit excellent tensile strength and strain-at-break, indicating that samples containing a high density of cells oriented along the tensile test direction facilitate the formation of superductility and an increase in tensile strength. Hence, a method that combines FIM with batch foaming has been proposed for improving the cellular structure and controlling the cellular orientation.