Effect of vacuum on mold filling in micro injection molding

Abstract

Micro injection molding is a widely used technique for mass production of micro plastic parts. As trapped air in the micro cavity may result in defects like short shot and voids, it is important to understand how trapped air can be eliminated to improve the replication of microstructures. This project investigates the effect of vacuum in the filling phase of micro injection molding by implementing a vacuum system to remove air in the cavity before mold filling. Two mold inserts of micro channels and micro holes were investigated. Micro channels of three different depth were fabricated using wire cut EDM method while an array of micro holes was fabricated by hot embossing method. Injection molding process was then carried out to produce the respective plastic parts and COC TOPAS 5013 L-10 was chosen as the material. Design of Experiment was performed to investigate the effects of parameter settings on the replication of microchannels and micro holes. The heights of protrusions on plastic parts were measured by using the Confocal imaging profiler. It is concluded that the use of vacuum venting does not have any significant effect on the replication ratio of micro channels and low-aspect-ratio micro holes. No obvious conclusion can be made from the fidelity of the micro holes.