Simulation of Injection Molding Process Considering Rheological Properties of Polypropylenes

The rheological properties of polypropylenes were measured using offline rheometers (a rotational rheometer and a capillary rheometer) and compared with those measured using an inline rheometer (injection molding rheometer). Shear viscosities from both offline and inline rheometers were similar in the high shear-rate region, but a remarkable difference was found in the low shear-rate region. Experiments and numerical simulations with Spiral and Flat molds were conducted to validate rheological properties of polypropylenes (PPs) measured from both rheometers. Comprehensively, the numerical simulation considering offline rheological data accurately predicted the actual injection-molded products in comparison to the case considering inline rheological data. Additionally, the effect of thermal conditions such as transition temperature and cooling water temperature on the flowability of molten PPs was investigated using spiral and flat molds. It is found that faster solidification of PPs decreased their flowability in Spiral mold and increased the maximum injection pressure in the Flat mold.