Visualization Study On Polymer Filling Flow Behaviors Of Injection Molding In Ring-shape Cavity

With the rapid development of Polymer Material Technology, the plastic injection products had played an important role in many major areas. However, the extensive use of the plastic injection products, such as optical lens visors and so on, was restricted by the air trapping defects along with the higher demands for the quality of the plastic injection products. During the injection molding process, the defects, such as weld-line, burn mark, silver mark, splay mark and so on, would generate because of air trapping phenomenon. However, now the dynamitic formation process and the mechanism of the air trapping phenomenon had not been studied clearly. In order to get a better understanding for the air trapping during polymer injection molding, the visualization experiments on the melt filling flow behaviors in the ring-shape cavity were conducted by the self-development visual ultrasonic assisted injection molding devices, the filling flow characters and the formation process of the air trapping were directly observed and recorded. The effects of injection parameters, mold structure and ultrasonic power on the air trapping phenomenon during PP melts injection molding were researched.First, the ring-shape product,3.5mm in thickness, was chosen as the research sample in this paper and a series of visualization experiments were conducted to record the PP melts filling process in the ring-shape cavity under different injection speed. The effects of injection speed on the filling characters were analyzed by comprehensive consideration, the changes of filling flow velocity and flow front shape during the melts filling the cavity. The results showed that the effects of different injection speed on injection molding behaviors of PP melts in ring-shape groove cavity were unlike. Under low injection speed, the melts filling velocity did not change obviously during injection molding process, while under the higher injection speed, the melts filling velocity appeared dynamic fluctuation and decreased rapidly at the later filling period. The flow front shape was also affected by the injection speed as well.In order to directly observe the formation and dynamic changes of the air trapping phenomenon, the annular mold cavity with boss was divided into two parts, the groove cavity 3.5mm in thickness and the boss cavity lmm in thickness, by the optimized design the ring-shape cavity. The effects of the injection parameters such as injection speed, mold temperature and melt temperature, on the melts air trapping behaviors during injection molding process were analyzed by visualization experiments. The experimental results showed that the increasing the injection speed can significantly improve the air trapping defects during injection molding annular products with boss, the effects of the mold temperature and melt temperature on air trapping defects were small and depended on the injection speed.The further visualization experiment research of the effects of flash groove and ultrasonic vibration on the air trapping characters had been conducted, the results showed that flash groove can effectively eliminate the air trapping defect independent of thickness of the flash groove, and ultrasonic vibration can improved the air trapping defects to a certain extent, the effects of ultrasonic vibration on air trapping defects under low injection speed was more significant than under the higher injection speed.