Because the wall thickness gauge is small and has small shrinkage, the injection molded automobile parts are tightly adhered to the mold. Due to the high injection speed, it is difficult to control the pressure holding time. Relatively thin wall thickness and stiffeners are also easy to be damaged during demoulding. The normal opening of automotive injection mold requires that the injection machine can provide sufficient mold opening force, which should overcome the resistance during mold opening.
1. The first is to overcome the direct mold opening force. During mold opening, the plastic will have a certain adhesion force parallel to the mold opening direction. This is because the plastic parts are not cooled enough when the automobile injection mold is cooled, and the elastic expansion of the cavity is not fully restored. The magnitude of this adhesion is related to the nature of the plastic, the surface quality of the mold, the demoulding slope, etc.
2. In addition, it is also necessary to overcome the indirect die opening resistance, that is, to overcome the pulling resistance in the core pulling process on the mobile side during die opening.
3. It can overcome the friction resistance caused by the movement of moving template and movable template of automobile injection mold.
4. Finally, it is also necessary to overcome the participation pressure of the mold cavity of the automobile injection mold. When opening the mold, the pressure of the mold cavity may not be equal to the atmospheric pressure, and the pressure in the mold cavity is not equal to the external pressure.
1. It is necessary to improve the design of automotive injection mold. Select appropriate die materials to improve the thermal strength and wear resistance of the die. Select reasonable die structure design and manufacturing, appropriately increase the thickness of push plate and middle backing plate, improve the die stiffness and reduce the elastic deformation of the die.
2. Automobile injection mold improves the manufacturing and matching accuracy of core pulling mechanism and motion system, reduces the surface roughness of cavity, core and punch components, and reduces the demoulding force. Because the thin-walled injection molded automobile parts require higher design and matching accuracy, interlocking devices are usually set to prevent the relative displacement of the mold core and cavity.
3. In order to design the gating system reasonably, the runner design should make the plastic parts transition from thicker area to thinner area in the injection process. It also needs to have enough exhaust ports.
4. In the injection process of plastic injection molding, try to reduce the internal stress of plastic parts, improve the injection speed and reduce the cooling speed. Therefore, it is necessary to increase the melt temperature and die temperature in order to relax the orientation. It is also necessary to select reasonable injection pressure, pressure holding time and cooling rate.