The Effects of Compression Pressure on Injection Compression Molding

Injection compression molding incorporates a mold compression action in the postfilling stage to compact the materials. The process is the same as the conventional injection molding in the filling and first stage packing. Packing stage continues until the gate material is frozen or the gate is shut off. Then, a mold compression action is engaged and continues to the end of the molding. With the mold compression, the pressure distribution inside the mold cavity can be uniform and the residual stresses caused by pressure gradients can be minimized. However, due to the non-isothermal cooling process, the compressibility of each place inside the mold cavity was not the same. At some time of the cooling process, the pressure at different points began to deviate from each other. In order to improve the non-uniform compression at later the stage of a ICM process, a two-stage compression method can be used. A disk mold was designed to study the effects of the two-stage compression on the molding product. It was found that less warpage can be obtained with a lower compression force at the second stage. The experimental results also suggested that there existed an optimal compression time that was corresponding to the time before the material solidification.