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What are the types of molds in terms of molding?

2025-08-29
Latest company news about What are the types of molds in terms of molding?

What are the major categories of molds in terms of molding? Molds are mainly divided into injection molding, compression molding, extrusion molding, injection molding, and hollow molding in terms of molding. In addition, there are foam plastic molding molds, glass fiber reinforced plastics, low-pressure molding molds, etc.

 

1. Injection molding

First, add the plastic into the heating cylinder of the injection machine. The plastic is heated and melted, and under the push of the injection machine screw or plunger, it enters the mold cavity through the nozzle and mold pouring system. Due to physical and chemical effects, it hardens and shapes into injection molded products. Injection molding consists of a cyclic cycle consisting of injection, pressure holding (cooling), and plastic part demolding processes, thus injection molding has the characteristic of periodicity. Thermoplastic injection molding has a short molding cycle, high production efficiency, and minimal wear of the mold caused by the melt. It can produce large quantities of plastic parts with complex shapes, clear surface patterns and markings, and high dimensional accuracy; However, for plastic parts with large variations in wall thickness, it is difficult to avoid molding defects. The anisotropy of plastic parts is also one of the quality issues, and all possible measures should be taken to minimize it as much as possible.

2. Compression molding

Commonly known as compression molding, compression molding, and compression molding, it is one of the earliest methods of forming plastic parts. Compression molding is the process of directly adding plastic into an open mold cavity at a certain temperature, then closing the mold and melting the plastic into a flowing state under the action of heat and pressure. Due to physical and chemical processes, plastic hardens into a shape and size that remains unchanged at room temperature.

3. Extrusion molding
It is a molding method in which materials in a viscous flow state are molded into continuous profiles with the desired cross-sectional shape at a lower temperature through a die with a specific cross-sectional shape under high temperature and certain pressure. The production process of extrusion molding involves preparing molding materials, extruding shapes, cooling and shaping, pulling and cutting, and post-processing of extruded products (quenching or heat treatment). During the extrusion molding process, pay attention to adjusting the temperature, screw speed, traction speed, and other process parameters of each heating section of the extruder barrel and the die head in order to obtain qualified extruded profiles. Special attention should be paid to adjusting the extrusion rate of polymer melt from the die of the machine head. Because when the extrusion rate of molten material is low, the extruded material has a smooth surface and uniform cross-sectional shape; But when the extrusion rate of the molten material reaches a certain limit, the surface of the extruded material will become rough, lose luster, and exhibit phenomena such as shark skin, orange peel patterns, and shape distortion. As the extrusion rate further increases, the surface of the extruded material undergoes distortion, and may even detach and fracture into molten fragments or cylinders. Therefore, controlling the extrusion rate is crucial.

4. Injection molding

Also known as casting and pressing molding. It is to add plastic raw materials into the preheated feeding chamber, then place the pressure column into the feeding chamber to lock the mold, and apply pressure to the plastic through the pressure column. The plastic melts into a flowing state under high temperature and pressure, and gradually solidifies into plastic parts through the pouring system into the mold cavity. This molding method is also known as transfer molding. Pressure injection molding is suitable for plastics that are lower than solid plastics and can be compressed and molded in principle. Pressure injection molding can also be used. But it is required that the formed material has good flowability in the molten state below the solidification temperature, and a larger solidification rate above the solidification temperature.