Development and application of rapid thermal cycling molding with electric heating for improving surface quality of microcellular injection molded parts

A rapid thermal cycling molding (RTCM) technology with electric heating and water cooling was developed to eliminate the surface defects of microcellular injection molded parts. To verify its effectiveness, an RTCM mold for producing microcellular cover plates was constructed. Experiments and simulations were conducted to evaluate the mold thermal response. The results show that the mold cavity surface temperature (TM) can be rapidly adjusted in a large range. Moreover, empirical correlations for predicting the TMs were proposed and validated, and then can be used as an effective tool to accurately control the TMs in actual molding. Finally, microcellular polyformaldehyde (POM) cover plates were molded. The effect of the TM on their surface roughness was investigated and relevant mechanism was analyzed. It is found that the part surface roughness can be effectively reduced by increasing the TM. When raising the TM close to or above 150 °C, the microcellular POM cover plates with glossy appearance comparable to the solid counterpart can be molded within an accepted molding cycle time, demonstrating the effectiveness of the developed molding technology.