There are many ways to classify automotive plastic moulds. According to the different methods of forming and processing plastic parts, they can be divided into the following categories.
The characteristic of the molding process of this plastic mold is that the plastic raw material is placed in the heating barrel of the injection machine.
The plastic is melted by heat, driven by the screw or plunger of the injection machine, enters the mould cavity through the nozzle and the pouring system of the automotive plastic mould, and the plastic is formed by heat preservation, pressure holding, and cooling in the mould cavity.
Since the heating and pressurizing device can function in stages, injection moulding can not only mould plastic parts with complex shapes, but also has high production efficiency and good quality. Therefore, injection moulding occupies a large proportion in the moulding of plastic parts, and injection moulds account for more than half of plastic moulding moulds. Injection machines are mainly used for the molding of thermoplastics, and in recent years have gradually been used for the moulding of thermoset plastics.
The characteristic of the molding process of this automotive plastic mould is that the plastic raw material is directly added into the open mold cavity, and then the mold is closed. After the plastic is in a molten state under the action of heat and pressure, the cavity is filled with a certain pressure.
At this time, the molecular structure of the plastic has a chemical cross-linking reaction, which gradually hardens and sets. Compression molds are mostly used for thermosetting plastics, and their plastic moulding parts are mostly used for the shells of electrical switches and daily necessities.
Transfer mold is also called pressure injection mold or extrusion mold. The molding process of this mold is characterized by adding plastic raw materials into the preheated feeding chamber, and then applying pressure to the plastic raw materials in the feeding chamber by the pressure column. The plastic melts under high temperature and high pressure and enters the cavity through the casting system of the mold. Chemical cross-linking reflects and gradually solidifies into shape. The transfer molding process is mostly used for thermosetting plastics, which can form plastic parts with more complex shapes.
The extrusion die is also called the extruder head. This kind of mould can continuously produce plastics with the same cross-sectional shape, such as plastic pipes, rods, and sheets. The heating and pressurizing device of the extruder is the same as that of the injection machine. The plastic in the molten state will form a continuous moulded plastic part through the machine head, and the production efficiency is particularly high.
In addition to the several types of automotive plastic moulds listed above, there are also vacuum forming moulds, compressed air moulds, blow moulds, low-foaming plastic moulds and so on.