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.

Integrated simulations of structural performance, molding process, and warpage for gas-assisted injection-molded parts. III. Simulation of cyclic, transient variations in mold wall temperatures

“…In addition, on the hollowed-core surface, S gc , located within a gas channel, the boundary condition must satisfy (11) where h N 2 and T N 2 are the heat transfer coefficient and the temperature of nitrogen injected during gas-assisted filling and packing phases, respectively. Along the mold cavity surface, it is subjected to a periodic boundary condition specified by the time-varying flux, J t ϭ J(t) Ϫ J av , at the cavity surface.…”

“…Simulation results on the secondary gas penetration by both C-GASFLOW and Moldflow/ gas show only very rough accuracy. A recent study 10,11 suggests that to obtain good simulation results for the secondary gas penetration in the gas-assisted packing stage, a new algorithm and a flow model of the shrinkage-induced origin may have to be introduced instead of just following the pressure-induced flow model used for the postfilling simulation of CIM.…”

The effect of fractures on gas injection in Hailar oilfield

“…Among them, the gas channeling is the most important factor affecting recovery (Mungan 1992;Amin et al 2010). Through a large number of pilot tests and laboratory experiments, the main causes of gas channeling in different types of reservoirs and different development stages are different, but all are affected by the development of fractures (Hao et al 2016;Chen et al 2015). Therefore, the evaluation and the prediction of reservoir fractures are the main factors, which control the effectiveness of channeling CO 2 gas flooding, which provides an important basis for the formulation of CO 2 flooding schemes (Cho and Lee 2017).…”

Study on the packing effects of external gas‐assisted injection molding on part shrinkage in comparison with conventional injection molding

“…Since the 1990s, gas‐assisted injection molding (GAIM), which operates at pressures lower than CIM, has offered numerous of advantages, including elimination of sink marks and warpage, reductions in part weight and shrinkage, and shorter cycle times [1–4]. In a typical GAIM process, ∼70–100% of the mold cavity volume is filled with molten resin, and then the gas is injected through the gas needle into the part's interior or into gas channels designed as part of the product.…”