The influence of processing parameters on thin-wall gas assisted injection molding of thermoplastic materials

Thin-wall gas assisted injection molding of thermoplastics has become an important process in industry because of its light weight, relatively lower resin cost per part, and faster cycle time. This report is devoted to investigate the effects of different processing parameters on the length of gas penetration in thin-wall gas assisted injection molded parts. The first part of this report is to find ways to optimize the gas penetration of molded parts. An L'18 experimental matrix design based on the Taguchi method was conducted to investigate the processing parameters that affect the length of gas penetration in thin-wall gas assisted injection molded parts. The second part of this report is to identify the relative significance of each processing parameter on the gas penetration of molded products. Two materials were used in the study: an amorphous acrylonitrile-butadiene-styrene (ABS), and a semi-crystalline polypropylene (PP). Experiments were carried out on an 80-ton reciprocating injection molding machine equipped with a high pressure gas injection unit. A plate cavity of various thicknesses (0.6, 1.2 and 2.0 mm) with a gas channel across the center was used for the experiments. After molding, the length of gas penetration in the molded parts was determined. For ABS materials, melt temperature and gas pressure were found to be the principal parameters affecting the thin-wall gas assisted injection molded parts, while for PP materials, the gas pressure and gas injection delay time were found to be the key processing parameters. In addition, warpage of molded parts was found to decrease with the length of gas penetration.