Development of Advanced Hybrid Polymer Melt Delivery Systems for Efficient High Precision Injection Molding

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.

The Development of a Pneumatic Stepping Motor Concept for Valve Based Flow Control During Injection Molding

To develop the control over mold filling during polymer melt manipulation, an alternative way of driving rotary plug valves, which were placed on mold runners, was investigated in this study. During the present investigation, the pneumatic stepping motor concept was explored by designing, fabricating, and testing a specific motor for a target injection molding base application. In order to improve the actuator performance, which is used to drive the valves, a stepping motor driven by a sequence of digital solenoid valves utilizing pressurized air was designed to enhance torque capacity and reduce energy consumption, while maintaining a fixed position for a long period of time. Similar to electromagnetic stepping motors, this pneumatic stepping motor can be driven by a simple switching circuit, which only moves one step for each driving signal without a fading rotation. This mechanism yields an effective system for speed and position control. Although the speed of pressurized air switching is limited by the response time of air solenoid valves that cause a lower rotation output speed, the holding torque and efficiency of this actuator was found to be relatively higher. By using a set of circular pistons aligned so as to actuate on axial wobble gear, the motor produced a very unique motion between the gear and rotor, causing the beneficial characteristics. In this study, the performance of the new motor was tested and compared to a similar size of electromagnetic stepping motor, as well. Thus, this study provides fundamental concepts to develop a suitable actuator for control valves in injection molding at low cost.