Gas-assisted injection molding: the effects of process variables and gas channel geometry

Polystyrene parts with different rib geometries but having the same aspect ratio were molded using gas-assisted injection molding (GAIM). The process variables that have an influence on the gas bubble distribution, residual wall thickness (RWT), fingering formation and mechanical properties were explored. The test results revealed that there is an inherent relationship between gas fingering and gas bubble penetration that has consequences on part strength. Shot size and delay time are the most dominant factors affecting the gas penetration, fingering formation, RWT and mechanical properties of the GAIM parts. The effects of rib geometries are also discussed. Computer simulation of the GAIM process was carried out using Moldflow, a commercial software. The outcomes predicted by simulation are compared with the experimental results. Based on the results, some useful design guidelines are suggested.