Injection molding is a standard manufacturing process for plastic parts. The most important process step, mold filling, involves unsteady nonisothermal flow of a non‐Newtonian molten plastic. Mold‐filling flow largely determines molecular orientation within the final part and thereby influences final part properties. This article describes techniques for successfully applying particle image velocimetry (PIV) to molten plastic flow during injection molding. The primary experimental challenges include the following: engineering optical access to the molten plastic flow at elevated temperatures (230–245°C) and pressures (∼20 MPa), finding particles that survive the thermal‐mechanical environment that melts the plastic, and developing experimental and data‐reduction techniques that allow multiple imperfect planar PIV measurements to be combined. Here, a custom optical‐access mold allowed mold center‐plane PIV to be performed in molten polystyrene. Simple statistical assessments of the velocimetry data and scaled residuals of the continuity equation suggest that the PIV can be conducted in molten plastics with an uncertainty of ±2%. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Simulations are often used to model polymer flow during injection molding to design molds and select processing parameters. It is difficult to determine the accuracy of these simulations due to a lack of experimentally measured in‐mold velocimetry and melt‐front progression data. This article compares the results from commercial mold‐filling simulation software to experimental data obtained via particle image velocimetry (PIV) in a special optical‐access mold with a rectangular cavity. Moldflow was used to simulate the mold filling by a polystyrene melt in the experimental configuration, and these simulated results are compared to the appropriately averaged time‐varying velocity field measurements. Simulated results for melt‐front progression are also compared with experimentally observed flow fronts. The ratio of the experimentally measured average velocity magnitudes to the simulation magnitudes was found on average to be 0.99 with a standard deviation of 0.25, and the difference in velocity orientations was found to be 0.9° with a standard deviation of 3.2°. The corner area opposite the gate was most problematic for the simulation. The region behind the front also had a relatively high simulation error, though not as severe as that in the corner. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers

Even though it is considered a mature technology, the commercial importance of injection molding continues to drive research on how processing parameters impact final part characteristics. In particular, the influence of flow phenomena, which largely control molecular orientation within the mold cavity, is not fully understood. Results are presented from a study of polymer flow during injection molding using a clear mold that allows optical access from three sides, in a standard commercial machine, under standard molding conditions for polystyrene. Comparisons are drawn between the experimental results and the predictions of a commercial code for global mold filling properties.

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