Effect of Gas-assisted-foaming Mechanism and Vent-area Design on Bubble-microstructure and Shrinkage of Polystyrene Foam-Injection Molding

This study investigates the effects of the vent-area on bubble-microstructure and shrinkage variation of gas-assisted foam-injection molding (GAFIM). The molding material is polystyrene (PS), and the gas foaming agent is nitrogen (N2). This study carried out the injection experiment with and without GAFIM to observe the molding characteristics of gas-filling pressure variation. In addition, the integration of vent-area volumes and cavity pressure measurement was developed to achieve foam growth and microstructure inside the sample to observe the effect of with and without vent-area on shrinkage variation and correlated pressure distribution near gate position during the filling process. The experimental results revealed that with the vent-area, the sample dimension shrinkage was relatively improved and the sample weight was reduced. On the other hand, the bubble-distribution increased with the changes in the volume of the vent-area and gas-filling pressure as the foam growth space increased.