Simulations and applications of injection-compression molding

A numerical algorithm is developed to simulate the injection-compression molding (ICM) process and to predict melt front advancement, the distributions of pressure, temperature and flow velocity. Processing characteristics were understood by changing processing parameters including compression speed, switch time from injection to compression, compression stroke, as well as initial cavity thickness and part thickness. The simulated molding pressures were also compared with those required by conventional injection molding (CIM). It was found that the compression speed and compression stroke are the two factors affecting the molding pressure most significantly. Switch time also shows apparent effect on the pressure profiles. Using lower switch time, lower compression speed and higher compression stroke will result in lower cavity pressures. The percentage reduction in molding pressure is higher if part becomes thinner when using ICM. The melt velocity far from the gate was found to be higher than that near the gate during the compression stage contrary to that of CIM resulting in different part residual stress and melt temperature distribution. The simulated pressures for both ICM and CIM show good coincidence with those obtained from cavity pressure measurements.