An investigation of real-time monitoring of shear induced cavity filling imbalances during polymer injection molding

Since the beginning of injection molding industry development, multi-cavity molding has been widely utilized to increase manufacturing efficiency, save time and reduce costs. As a result, geometrically balanced mold cavities and runner systems have become industry standards for injection molding. Some seemingly balanced designs, however, still provide imbalanced cavity filling results. The reason for the imbalanced filling is due to the shearing between the lamellae of the molten polymer as it is injected through the runner system and into the mold cavities. The current investigation includes visual studies of how the shearing of the polymer through the runner systems affects the mold filling in real time. In order to develop a deeper understanding of the shear induced imbalances in injection molding, a custom built mold incorporating transparent mold inserts and runner systems was used. Polymers were injection molded into different types of cavities and the cavity filling was documented in real time via a high-speed camera. With this study, there is a potential to find and/or verify methods to mitigate the non-uniform behavior of molten polymers undergoing shear thinning or shear heating, especially since the imbalances have the potential to alter properties of the finished products.