Equipment development and experimental investigation on the cellular structure of microcellular injection molded parts

Using newly developed microcellular injection molding equipment, microcellular foamed polystyrene tensile test bars were molded. The cellular structure on the fractured surfaces of three positions on the effective test zone of molded bars was investigated. It was demonstrated that a foamed core and unfoamed skin regions exist on the molded bars. Then, three processing parameters, the nozzle temperature, injection speed and shot size, were investigated in terms of their effects on the cellular structure and skin layer thickness of the microcellular injection molded parts. The results showed that finer and more uniform cell structure is formed at appropriate nozzle temperatures (165-180 °C in this work). Cell diameter decreases, cell density increases and cellular structure uniformity improves with the increase of injection speed or shot size. Moreover, increasing the injection speed leads to the gradual decrease of skin layer thickness. Shot size does not show significant influence on skin layer thickness.