Experimental and numerical analysis of the flow fronts advancing in micro injection molding weld line developing process

摘要

Understanding the weld line forming process is important for micro parts molded by injection molding technology. In this paper, the flow fronts advancing during weld line forming process of micro injection molding is investigated by both experimental and numerical methods. A glass insert flow visualization mold is devised to record the whole process of the melts flowing and weld line forming. Arburg® 220S is chosen as the micro injection molding machine and PP is the objective material. The molding part is a micro dumbbell tensile sample, which is totally 24 mm long and has 12 mm long micro scale test area with rectangular cross section (0.4 mm width×0.1 mm depth). The numerical simulation is realized by software Comsol® Multiphysics 3.4 taking surface tension account into. In order to find out how the processing parameters affect weld line forming in micro scale, the experiments were carried out in different processing conditions, injection pressure (25, 30, 35, 40 MPa), injection speed (15, 20cm3/s), mold temperature (120, 135°C). Flow visualization experimental analyses indicate that injection pressure, injection speed and mold temperature all have effects on the flowing speed of the melts. Injection pressure and mold temperature also influence with the shape of flow fronts. Numerical simulation results give a good confirming description for the flow fronts shape which is consistent with experimental observation. In addition the characteristic prediction for the v notch size is carried out.