Experimental and numerical study of the melt viscosity during the injection molding process
Florin Ilinca, Abdessalem Derdouri, Hetu Jean-Francois
National Research Council Canada
Canada

Keywords: simulation, injection, viscosity

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This work is part of a continuing effort to obtain a better understanding of the rheological behavior during the injection molding of unfilled and reinforced polymers and help improve the prediction of three-dimensional (3D) numerical simulation. Two pressure sensors were mounted flush on the slightly tapered rectangular sprue of a center gated plate mold to monitor the time evolution of the wall shear stress prior to entering the cavity. After an initial rise, the wall shear stress in the sprue remains relatively constant during the filling stage of the mold. The transient shear viscosity was determined from the known volumetric rate using a simplified isothermal flow approach and compared to the viscosity measured by traditional off-line rheometers. Flow in the sprue is also computed using a 3D finite element code and the predicted pressures are used in combination with the simplified theory to calculate the viscosity. This serves as a validation for both the numerical approach and the simplified theory used to recover the viscosity from the pressure drop in the sprue. Finally, non-isothermal effects are studied using the numerical simulation for different melt/mold temperatures. The resulting viscosity model is used to obtain numerical solutions for the complete filling of the cavity.