The Research Of Screw Head Assembly In Injection Molding Of Microstructures

The micro structure of injection molding is a new molding technology. The precise control of injection quantity is required. The main factors affecting the injection quantity are molding temperature, injection speed, injection pressure and holding pressure. Injection molding screw head assembly plays a very important role in forming pressure speed during injection molding. The non-return valve is applied to ensure the precision of shot weight and its sensitivity of opening and closing has an important influence on repeat precision of the quality of injection molding products.In order to improve the sensitivity of opening and closing of non-return valve and precise control the injection quantity, this paper made the structure parameters of the ring non-return valve of the micro injection molding machine to be selected priority using numerical simulation method and made the sensitivity of its opening and closing during plasticization and injection is best.9different structural parameters of the non-return valve is designed, it is from four aspects which are the ratio between screw groove of the cross sectional area and non-return valve circulation sectional area, the angle between screw axis and contact surface of non-return valve and sealing ring, the displacement of non-return valve, whether there is groove in the inner surface of non-return valve. Based on the physical model and the finite element model of flow channel which is built using Solidworks and Gambit, numerical simulation of three-dimensional flow in channel of9different structural parameters of non-return naive in micro injection molding machine were performed in the Polyflow. The flow is generalized by the Newtonian isothermal fluid. In addition, to research the influence of injection speed on closing of non-return valve, the numerical simulation of non-return valve1under different injection speed were performed and the experimental study was done. By analysis and comparison of the calculation and the experiment results, the following conclusions is reached:1. The variation and value of pressure difference on both sides of non-return valve play an important role in its opening and closing during plasticizing and injecting.2. When the structure parameters of non-return valve which affect the variation and value of pressure difference on its both sides were selected, the ratio between screw groove of the cross sectional area and non-return valve circulation sectional area equals1.0, the angle between screw axis and contact surface of non-return valve and sealing ring is60°, the displacement of non-return valve equals approximately1.5times of spiral groove depth at screw homogeneous section is most appropriate, the pressure difference on both sides of non-return valve can be increased by reducing the non-return valve diameter instead of the trench.3. If the quality of the products is ensured, on the premise, the higher injection speed, the pressure difference on both sides of non-return valve is bigger, the non-return valve is closed more quickly, the leakage of the melt is smaller.