Energy-efficient micromolding and in-mold compounding using ultrasonic vibration energy with enhanced material flow

Abstract

Injection molding is the most widely used polymer processing technology, and uses thermal energy to plasticize thermoplastic polymer pellets. In this study, ultrasonic vibration energy was used to plasticize polymer pellets in micro-injection molding, instead of using conventional thermal energy. An auxiliary flow unit was used to enhance the ultrasonic plasticizing effect and the relevant flow rate. Two rotor types, flat and blade-type rotors, were investigated in terms of flow enhancement capability and the resulting improvement in the quality of the molded parts. As a result, the blade-type rotor showed improvements in flow rate (by 66%) and filling length (by 26.5%). This enhanced material flow in ultrasonic micromolding was then further applied to in-mold compounding and molding by dispersing short carbon fibers (CFs) into polypropylene (PP) pellets during ultrasonic plasticizing. The resulting CF composites showed a 38% improvement in tensile strength compared to pure PP specimens. Considering that this ultrasonic micromolding was performed by a desktop-scale machine with low energy consumption, this process is more efficient for micromolding than the conventional injection molding process.