Warpage Deflection and Birefringence of a Thin PMMA Injection-Molded Product

• Main Authors: You-Jie Lai, 賴祐杰
• Other Authors: 沈君洋
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/68471832497703201580

碩士 === 國立中興大學 === 機械工程學系所 === 94 === An injection mold with a rectangular cavity (62.5*25*2 mm) was designed and manufactured. The mold cavity can be vacuumized during injection molding. The key points in the mold design to achieve a gastight condition for the cavity is discussed. Injection rate, packing pressure and mold temperature were the three variables in the experiment. The specimen were measured by a coordinate measuring machine (CMM) and a polariscope respectively. The warpage deflection and birefringence were obtained. For the CMM measurement, the result reveals that the warpage deflection increases with the mold temperature. The effect of injection rate on the warpage deflection appears to be insignificant. For lower mold temperatures (35℃and 50℃), the warpage deflection decreases with an increase of the packing pressure；for a higher mold temperature (80℃), on the contrary, the warpage deflection increases with the packing pressure. For the polariscope measurement, the result indicates that the packing pressure is the most important factor affecting the birefringence. The birefringence appears to increase with the packing pressure. For operations with the packing pressure less than 30%, only a small region near to the injection gate would have a significant birefringence effect. The mold temperature and injection rate also affect the birefringence. However, their effects are minor. In the present consideration, the thickness of the specimen is 2 mm. For this condition, the application of the vacuum process to the mold cavity does not improve either warpage deflection or birefringence.