Controlled low pressure injection molding is characterized by its distinction from conventional injection molding. The conventional injection molding filling stage controls the injection rate, while the low pressure injection molding filling stage controls the injection pressure.
During the low-pressure injection process, the inlet pressure of the cavity is constant, but the injection rate is changed, and the injection is started at a very high speed. As the injection time is prolonged, the injection rate is gradually reduced, so that the internal stress of the plastic part can be largely eliminated. To ensure the accuracy of plastic parts. At high speed injection, the shear viscous heat generated by the high-speed flow of the melt increases the melt temperature and lowers the melt viscosity, making it possible to fill the cavity at low pressure. Since the low pressure injection is melt filling based on a constant pressure, the low pressure injection machine has its unique hydraulic system.
In order to achieve low-pressure high-speed molding, it is necessary to improve the injection system of the traditional injection molding machine. At present, a multi-cavity hydraulic injection system has been developed abroad, and its main functions are:
(1) The maximum injection pressure can be changed in multiple stages under the same oil pressure;
(2) High-speed injection can be performed under low injection pressure.
Since the basic principle of low-pressure injection molding is the same as that of general injection molding, the molds used in the two molding methods are identical in structure. However, low-pressure injection molding uses low-pressure filling, and there is no pressure peak, which can avoid breakage or damage of the small core, which is beneficial to improve the service life of the mold.
On the other hand, due to the low wear of the low pressure injection molding on the mold, the temperature control and the exhaust of the mold are not very high. It can be made of zinc-aluminum alloy material and simple injection mold, which not only can reduce the production cost, but also can quickly produce small batches of precision plastic parts to meet the needs of multi-variety and small-scale production on the market.