Knowledge Bank

Gas-assisted injection molding (GAIM) is a process where a molten polymer is injected into a cooled mold cavity followed by an injection of gas, allowing the polymer to fill the cavity and form a hollow part as it cools and solidifies. Current GAIM simulations for non-isothermal Newtonian fluids can accurately predict the coating thickness of the polymer melt. However, no existing models predict the behavior of non-isothermal non-Newtonian fluids. The proposed simulations use known material and system properties and process variables such as mold temperature, melt temperature, and pressure, to calculate the temperature and velocity profiles to predict the coating thickness using derived relations. Experiments have been performed to determine the effect of temperature gradients and rheological behavior of the penetrating fluid. The experimental data was compared against the simulation for both Newtonian and shear-thinning fluids utilizing various viscosity models to describe the behavior of the fluids and showed that the simulations were reliable in predicting the fractional coverages at higher rowlengths. Velocity and temperature profiles were calculated in which the non-isothermal behavior of the system was shown to be predicted by the simulation. In addition, viscosity vs shear rate plots were created to validate the assumed behavior of the tested fluids for more accurate modeling. Simulated vs experimental results are plotted for the cross-exponential viscosity model for both polycarbonate and polystyrene at various rowlengths, and additionally the Ellis and power law viscosity models for polystyrene. An accurate simulation will help to reduce production costs and improve product quality.