Simulations of primary and secondary gas penetration for a gas-assisted injection-molded thin part with gas channel

Abstract

Numerical simulations and experimental studies concerning melt flow and primary as well as secondary gas penetration during the filling and the postfilling stages in gas-assisted injection molding of a thin plate with a semicircular gas channel design were conducted. Distribution of the skin melt thickness along the gas-penetration direction was measured to identify primary and secondary gas penetration. Melt and gas flow within the gas channel of a semicircular cross section is approximated by a model which uses a circular pipe of an equivalent hydraulic diameter superimposed on the thin part. An algorithm based on the control-volume/finite-element method combined with a dual-filling parameter technique suitable for the tracing of two-component flow-front advancements is utilized and numerically implemented to predict both melt- and gas-front advancements during the melt-filling and the gas-assisted filling processes. A flow model of the isotropic melt-shrinkage origin combined with a gapwise layer tracing algorithm was implemented to assist the prediction of secondary gas penetration and melt flow in the post-filling stage. Simulated results on the gas front locations at the end of both primary and secondary penetration phases show reasonably good coincidence with experimental observations.