| Summary: | 碩士 === 國立交通大學 === 機械工程系所 === 107 === With the rapid development of Computer, Communication Consumer (3C) Electronics Industry, the demands for optical products is increasing. The most representative products are the optical lenses. Generally, the method to produce lenses was using injection molding. However, there is a large difference in shape thickness for the characteristics of lenses, and a complicated shrinkage due to the uniformity of temperature and pressure distribution in the cooling stage of the injection molding, so the accuracy was difficult to control. Therefore, how to massively manufacture optical lenses with high precision has become an important issue.
In order to investigate the distribution and the influence of the polymer melt state in the cavity during the injection molding process. By using the injection mold-flow analysis software Moldex3D and drawing software SolidWorks to build a model framework for numerical simulation analysis, and verify with experiments. The material used in this Study was optical grade polymethyl methacrylate (PMMA). The experimental measurement used the K-type thermocouples that produced by a Japan company, MISUMI, and the temperature and pressure sensors from KISTLER in Switzerland to measure the temperature and pressure at different positions in the cavity, and the diameter of the sensing end is only 1mm in diameter. The effect of the sensors on the shaped lenses surface can be minimized and the monitoring positions were the same as the sensing nodes that embedded in the numerical simulation.
The numerical simulation results showed that increasing the mold temperature can effectively reduce the temperature gradients in the molded parts. In addition, the temperature results of different areas of the molded parts showed that the farther away from the gate, the higher the temperature, and the center temperature was higher than the surrounding temperature, and the surrounding temperature was distributed symmetrically to the direction of the molding. The gate freeze time was 0.7 second at injection pressure of 400 bar and mold temperature of 40 ℃, and the time required for the gate to freeze was increased as the mold temperature increases. Increase the packing pressure also raise the pressure peak in the cavity. The temperature measurement results of the thermocouples showed that the temperature of the near gate and the far gate measured at five different buried depths will be also increased with the melt filling; when the end of the thermocouples exceeds 5 mm below the mold surface, it can be considered as the mold temperature. Furthermore, through the cold mounting experiments, it was found that the actual temperature measurement point of the end sensed point of the thermocouple products was 0.75 mm from the tip of the thermocouples, and the length of the temperature measurement point was 5.45 mm. The temperature and pressure sensors measurement results showed that the gate solidification point can be clearly observed at the near gate, but not at the far gate; In terms of temperature distribution, the results measured by the temperature and pressure sensors were closed to the simulation results compared with the results of the thermocouples measurement.
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