Computer simulation of the filling process in gas‐assisted injection molding based on gas‐penetration modeling

Abstract

Gas-assisted injection molding can effectively produce parts free of sink marks in thick sections and free of warpage in long plates. This article concerns the numerical simulation of melt flow and gas penetration during the filling stage in gas-assisted injection molding. By taking the influence of gas penetration on the melt flow as boundary conditions of the melt-filling region, a hybrid finite-element/finite-difference method similar to conventional-injection molding simulation was used in the gasassisted injection molding-filling simulation. For gas penetration within the gas channel, an analytical formulation of the gas-penetration thickness ratio was deduced based on the matching asymptotic expansion method. Finally, an experiment was employed to verify this proposed simulation scheme and gas-penetration model, by comparing the results of the experiment with the simulation.

Effects and optimization of processing parameters in water‐assisted injection molding

“…Over a period of recent years, fluid‐assisted injection molding technologies, including gas‐assisted1–6 and water‐assisted7–18 injection molding, have attracted more and more attention in researches and applications, due to that they offer potential to the production of complex, highly integrated parts in virtually one process step. Water‐ and gas‐assisted injection molding (WAIM and GAIM) are similar processes and they both utilize high‐pressure fluids with viscosities much lower than the polymer melt viscosity to displace the polymer melt within thick sections of the cavity.…”

A study on the distinguishing responses of shrinkage and warpage to processing conditions in injection molding

“…Pressure and temperature history throughout the part was calculated from the constitutive equations of mass, momentum and energy, with specific assumptions and boundary conditions for each particular stage. For example, the governing equations for the filling stage are written as35–37 where $ \dot {\varepsilon }_{ij} = {1\over 2}(u_{i,j}+u_{j,i}) $ ; the symbol ‘,’ denotes derivatives, i = 1,2,3 and j = 1,2,3 are the coordinate components; u , P and T are velocity, pressure, and temperature with η, ρ, C p and K being dynamic viscosity, density, specific heat, and the thermal conductivity, respectively.…”

“…The basic assumptions for the filling stage can be given as: (a) melt is incompressible and purely viscous; (b) inertia force is neglected when compared with viscous force. In addition, the following boundary conditions were adopted: (a) the polymer will remain the mold temperature once it contacts the mold wall, therefore the heat resistance between the mold wall and polymer melt is neglected; (b) a nonslip condition applied during both filling and postfilling stage, i.e., the flow rate of the polymer at the mold wall is assumed zero 35–37…”

“…Pressure and temperature history throughout the part was calculated from the constitutive equations of mass, momentum and energy, with specific assumptions and boundary conditions for each particular stage. For example, the governing equations for the filling stage are written as [35][36][37]…”

“…In addition, the following boundary conditions were adopted: (a) the polymer will remain the mold temperature once it contacts the mold wall, therefore the heat resistance between the mold wall and polymer melt is neglected; (b) a nonslip condition applied during both filling and postfilling stage, i.e., the flow rate of the polymer at the mold wall is assumed zero. [35][36][37]…”