Research Of Rapid Heat Cycle Molding Technology And Heat Transfer Analysis

Due to the high productivity, low cost and the flexibility to wide variety of shapes, injection molding has become one of the most widely used processing technologies in plastic manufacturing industry. However, with the rapid growth of home electronics, communications device, electronics products, automotive, optoelectronics products, people have the requirement of much thinner and more complex parts which should also meet the high demand of the consumer on their appearance and strength and the conventional injection molding has been unable to meet this trend. Rapid Heat Cycle Molding (RHCM) is a new injection molding technology which uses the dynamic mold temperature control method. During the heating stage of RHCM, the mold surface is heated to a high temperature to make the melt fill cavity at this temperature and hence facilitate the filling and flowing of the melt. During the cooling stage of RHCM, the shaped melt is cooled down quickly by coolant to reduce the cycle time. The RHCM technology could produce plastic parts with high surface quality, such as no weld line, no flow mark, high surface gloss, on basis of guaranteeing the productivity. Furthermore, RHCM could be used in producing thin-wall parts and parts with microstructure.For RHCM, the heating/cooling efficiency and the temperature uniformity of the mold could affect productivity and the quality of the final part significantly. Therefore, research on how to improve the heating/cooling and the temperature uniformity has great significance in the application of RHCM. This thesis mainly studied the key technology of Steam-assisted heating Rapid Heat Cycle Molding (SRHCM) and Electric-heating Rapid Heat Cycle Molding (ERHCM). The heating and cooling thermal response rule were evaluated. Discussed the factors influenced the temperature uniformity through finite element analysis. Finally, the numerical simulation results were verified through experimental producing.The process principle of RHCM was studied through comparing RHCM with conventional injection molding. The advantages and disadvantages of various dynamic temperature control methods were studied and compared. The processes of Steam-assisted heating Rapid Heat Cycle Molding and Electric- heating Rapid Heat Cycle Molding were designed.The finite element analysis model of Steam-assisted heating Rapid Heat Cycle Molding mold was constructed. The thermal response during heating and cooling stage was simulated based on ANSYS. The influence of heating/cooling channels' diameters and arrangements to heating/cooling efficiency and the temperature uniformity was evaluated. The results showed that the effective heating time, cooling time, heating speed, cooling speed of SRHCM are 30s, 40s, 4.3℃/s and 4.9℃/s respectively. When the mold was heated by steam of 180℃, its temperature had an upper limit value and the upper limit temperature was about 170℃. Furthermore, heating/cooling efficiency and the temperature uniformity could be improved by channels with small diameters and tight arrangements.The SRHCM technology used in producing liquid crystal display panel was studied as an actual example. The thermal response during heating and cooling stage was simulated respectively through constructing the thermal response analysis model. It could be concluded that the heating time of SRHCM mold is about 20s when the temperature of the mold surface was 110℃. The cooling time of the SRHCM mold is about 35s when the melt was cooled to 85℃. Finally, the simulation results were applied to practical SRHCM producing to verify its veracity.The Electric-heating Rapid Heat Cycle Molding with electric heating and cold water cooling was studied. The ERHCM mold was designed and the finite element analysis model was constructed. The transient thermal transfer was studied based on ANSYS. The simulation results showed that, when the mold was heated with electric, the average heating speed could reach 7.3℃/s and the mold surface could be heated with no upper limit temperature. During the cooling stage, the average cooling speed of the melt was about 4.1℃/s and the melt had good temperature uniformity.