An empirical study of gas penetration in full-shot gas-assisted injection moulded parts

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 effects of different processing parameters on the length of gas penetration in full-shot gas-assisted injection moulded parts. The first part of this report shows how the gas penetration of moulded parts is optimized. An L′18 experimental matrix design based on the Taguchi method was conducted to investigate the processing factors that affect the length of gas penetration in full-shot moulded parts. The second part of this paper identifies the relative significance 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 affecting 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.