ABSTRACT:Full-shot gas-assisted injection-molding has the advantage of eliminating the switchover mark that usually occurs on the surface of short-shot gas-assisted molded parts. The purpose of this report was to study the effects of processing parameters on the moldability of the full-shot gas-assisted injectionmolding process. Experiments were carried out on an 80-ton injection-molding machine equipped with a high-pressure nitrogen-gas injection unit. The materials used were general-purpose polystyrene and polypropylene. A plate cavity with a gas channel of various geometries (trapezoid, semicircle, and rectangle) across the center was used to mold the parts. After molding, the lengths of gas penetration were determined. The hollowed core ratio by the gas was also determined. A numerical analysis was carried out to find out the temperature distribution of the polymer melt inside the gas channel. It was found that the sink mark of molded parts decreases with the length of gas penetration. Molded parts using trapezoidal gas channel had the longest gas penetration length. In addition, a thermal contraction model was proposed to predict the gas penetration volume

Full-shot gas-assisted injection moulding has increasingly become one of the most important methods used to produce plastic components. It has the advantage of eliminating the switchover mark, which usually occurs on the surface of short-shot gas-assisted injection moulded parts. This paper is devoted to an investigation of the eVects of diVerent processing parameters on the length of gas penetration in full-shot gas-assisted injection moulded parts. The ®rst part of this report shows how the gas penetration of moulded parts is optimized. An L 0 18 experimental matrix design based on the Taguchi method was conducted to investigate the processing factors that aVect the length of gas penetration in full-shot moulded parts. The second part of this paper identi®es the relative signi®cance of each processing parameter on the gas penetration of moulded products. The materials used were general-purpose polystyrene and polypropylene. Experiments were carried out on an 80 ton injection-moulding machine equipped with a high-pressure nitrogen gas injection unit. For the factors selected in the main experiments, melt temperature, gas injection delay time and gas hold time were found to be the key processing parameters aVecting the length of gas penetration in full-shot gas-assisted injection moulded parts. In addition, the sink mark of full-shot moulded parts decreases with the length of gas penetration. Bending strength of full-shot gas-assisted injection moulded parts is higher than that of short-shot moulded parts.