Heating-mechanism of gas, short-shot method, and their experimental and benefit analysis on hollow structure of gas-assisted injection-molded specimens

Abstract Gas-assisted injection molding (GAIM) introduces high-pressure gas into the mold cavity after molten plastic injection, creating a hollow structure that reduces material usage and improves warpage and cooling deformation, particularly in thick-walled parts. However, conventional GAIM typically employs nitrogen at around 15 °C, which often leads to condensation and pressure drops due to the temperature difference with the molten polymer. These issues result in unstable gas penetration, asymmetric hollow structures, reduced dimensional stability, and surface defects from insufficient gas support. To address these challenges, this study integrates a gas heating module into the GAIM process and systematically evaluates its effects using the short-shot method and spiral-flow specimens. Experimental results show that gas preheating reduces solid material usage by more than 6 % and achieves an average weight reduction above 20 %, attributed to slower cooling and enhanced hollow formation. Heated gas also decreases shrinkage variability by over 20 %, lowers the overall shrinkage rate by ∼5 %, and simultaneously reduces melt pressure by ∼10 % while stabilizing gas output by ∼15 %, thereby improving dimensional stability and process robustness. Furthermore, the hollow ratio is increased by 15–20 % and penetration length is extended by ∼20 %, resulting in more continuous, symmetric, and well-defined hollow structures.