Investigation of internal water cooling on gas bubble behavior in the gas-assisted injection molding process.

摘要

In contrast to the conventional injection molding process, gas-assisted injection molding (GAIM overcomes many processing defects such as warpage, sink marks and high filling pressure by introducing a gas before complete filling takes place. In this study an internal cooling medium, such as water was introduced in conjunction with GAIM and resulted in an improvement of the GAIM process.; Instant cooling along the gas channel prevents unwanted rupture of the melt surface by introducing water because the frozen melt layer resists breaking the melt interface due to the high-pressure gas. Consequently, the control of the gas and the water is the major task to achieve the optimum process for gas-assisted injection molding with internal cooling (GAIMIC).; The major goal of this study was to investigate gas bubble behavior, such as gas penetration and gas fingering for the semi-crystalline materials, HDPE and PP, and an amorphous material, PC, by introducing water into the conventional gas-assisted injection molding system. A computer based pressure-control GAIM controller was constructed and developed to adapt to the introduction of water. A statistical experiment using a five-factor half-fractional factorial design was performed to determine the effects of five processing parameters: shot size, water volume, gas injection pressure, gas injection time, and gas delay time. One parameter model was designed to further study the effect of water on gas bubble behavior. CAE simulations were conducted to obtain the optimum processing conditions for the GAIM process before performing the design of the experiments.; Based on analyzing normal probability plots and Pareto charts, shot size was the most significant effect on gas penetration length and gas fingering area. Gas delay time, shot size vs. water volume interaction, gas injection time vs. gas delay time interaction, and water volume vs. gas delay time interaction were significant factors affecting the length of gas penetration in the GAIMIC process. On the gas fingering area, water volume, shot size vs. water volume interaction, and water volume vs. gas injection pressure interaction were major factors. In one parameter design of the experiment, the gas fingering area decreased with increasing water volume. However, the relationship between water volume and gas penetration was not clear.