Thermal response of an electric heating rapid heat cycle molding mold and its effect on surface appearance and tensile strength of the molded part

摘要

Rapid heat cycle molding (RHCM) is a newly developed injection molding technology in recent years. In this article, a new electric heating RHCM mold is developed for rapid heating and cooling of the cavity surface. A data acquisition system is constructed to evaluate thermal response of the cavity surfaces of the electric heating RHCM mold. Thermal cycling experiments are implemented to investigate cavity surface temperature responses with different heating time and cooling time. According to the experimental results, a mathematical model is developed by regression analysis to predict the highest temperature and the lowest temperature of the cavity surface during thermal cycling of the electric heating RHCM mold. The verification experiments show that the proposed model is very effective for accurate control of the cavity surface temperature. For a more comprehensive analysis of the thermal response and temperature distribution of the cavity surfaces, the numerical-method-based finite element analysis (FEA) is used to simulate thermal response of the electric heating RHCM mold during thermal cycling process. The simulated cavity surface temperature response shows a good agreement with the experimental results. Based on simulations, the influence of the power density of the cartridge heaters and the temperature of the cooling water on thermal response of the cavity surface is obtained. Finally, the effect of RHCM process on surface appearance and tensile strength of the part is studied. The results show that the high-cavity surface temperature during filling stage in RHCM can significantly improve the surface appearance by greatly improving the surface gloss and completely eliminating the weld line and jetting mark. RHCM process can also eliminate the exposing fibers on the part surface for the fiber-reinforced plastics. For the high-gloss acrylonitrile butadiene styrene/polymethyl methacrylate (ABS/PMMA) alloy, RHCM process reduces the tensile strength of the part either with or without weld mark. For the fiber-reinforced plastics of polypropylene (PP) + 20% glass fiber, RHCM process reduces the tensile strength of the part without weld mark but slightly increases the tensile strength of the part with weld mark.