Analysis of Pressurized Cavity on Replication of Micro-Patterns with Injection Molding

Abstract

First, we studied the effect of the cavity air pressure on the replication of micro-patterns in injection molding. When pressure is applied to the cavity air, the pressure at the flow front is increased and air surging in the mold channel occurs according to the injection rate and the cavity pressure. The pressure of the air trapped inside the micro-pattern is increased due to the decrease in volume in accordance with the progress of the pattern replication. The pressure gradient to the pattern direction with the cavity air pressure is larger than the case of non-pressurized. Therefore, the hesitation is reduced with the cavity air pressure resulting in the improvement of replication of the microscopic pattern. In this investigation, we carried out experiments for molds with a macroscopic pattern (ribs) and a microscopic pattern. In order to evaluate the quality of replication, we measured the filling heights of patterns with different ratio of the cavity air pressure to the injection pressure. The experimental results showed that the application of cavity pressure helps the replication of patterns both for macroscopic and microscopic scales. Second, numerical study was performed on the fluid flow with pressurized cavity air. The air flowing gap is modeled in order to implement the effect of the air surging. The pressure gradient through the micro-pattern was calculated when the flow front passes the micro-pattern. Numerical analysis was performed with respect to the various injection rates (0.24, 0.36, 0.48m/s) and a variety of mold inner pressure (0.1, 1, 4MPa). The height of the micro-pattern according to the injection speed and the cavity air pressure was analyzed for comparing the enhancement of replication.