Abstract

A novel melt manipulation “RheoDrop” concept for hot runner injection molding is presented. In this concept, a controlled rotational shear is applied to a polymer melt in the hot drop to reduce its viscosity without raising the temperature. This is achieved by providing a transient rotational motion to the valve pin in the hot drop. This strategy is developed to mitigate issues associated with cold slug formation during injection molding in hot runner systems. The cold slug formation is particularly relevant for injection molding of engineering plastics such as liquid crystal polymers (LCPs) for medical and electronic applications. Analytical and experimental investigations were performed to validate the concept. The efficacy of the concept is assessed analytically utilizing a combination of two software modules, autodesk, moldflow and ansys fluent. The results confirmed that the concept was able to produce enough shear to reduce the dynamic viscosity between injection molding cycles. A prototype RheoDrop system was designed and developed and retrofitted in a four drop hot runner system mold to experimentally validate the concept. Preliminary experiments were performed utilizing acrylonitrile butadiene styrene, and parts were successfully fabricated at temperatures that are too low for traditional molding in a hot runner system.

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