SIMULATIONS OF PRIMARY AND SECONDARY GAS PENETRATION FOR A GAS-ASSISTED INJECTION-MOLDED THIN PART WITH GAS CHANNEL

Numerical simulations and experimental studies concerning melt flow an d primary as well as secondary gas penetration during the filling and the postfilling stages in gas-assisted injection molding of a thin pla te with a semicircular gas channel design were conducted. Distribution of the skin melt thickness along the gas-penetration direction was me asured to identify primary and secondary gas penetration. Melt and gas flow within the gas channel of a semicircular cross section is approx imated by a model which uses a circular pipe of an equivalent hydrauli c diameter superimposed on the thin part. An algorithm based on the co ntrol-volume/finite-element method combined with a dual-filling parame ter technique suitable for the tracing of two-component flow-front adv ancements is utilized and numerically implemented to predict both melt -and gas-front advancements during the melt-filling and the gas-assist ed filling processes. A flow model of the isotropic melt-shrinkage ori gin combined with a gapwise layer tracing algorithm was implemented to assist the prediction of secondary gas penetration and melt flow in t he post-filling stage. Simulated results on the gas front locations at the end of both primary and secondary penetration phases show reasona bly good coincidence with experimental observations. (C) 1998 John Wil ey & Sons, Inc.