Mold molding refers to the production of parts and products by making and using molds. Mold molding can be divided into several different types, compression molding, injection molding, extrusion molding, pressure injection molding, hollow molding, die casting molding and so on.
(1) Compression molding
Commonly known as pressing molding, is one of the methods of molding plastic parts. Compression molding is to add plastic directly into an open mold cavity with a certain temperature, and then close the mold, and the plastic melts into a flowing state under the action of heat and pressure. Due to physical and chemical effects, the plastic is hardened into a plastic part with a certain shape and size that remains unchanged at room temperature. Compression molding is mainly used for molding thermosetting plastics, such as phenolic molding powder, urea formaldehyde and melamine formaldehyde molding powder, glass fiber reinforced phenolic plastic, epoxy resin, DAP resin, silicone resin, polyimide and other molding compounds, can also be molded and processed unsaturated polyester mass (DMC), sheet molding compound (SMC), prefabricated integral molding compound (BMC) and so on. Under normal circumstances, the compression mold is often divided into three categories: overflow type, non-overflow type and semi-overflow type according to the matching structure of the upper and lower molds of the compression film.
(2) Injection molding
The plastic is first added to the heating barrel of the injection machine. The plastic is heated and melted. Under the push of the injection machine screw or plunger, the plastic enters the mold cavity through the nozzle and the mold gating system, and is hardened and shaped into injection molded products due to physical and chemical effects. Injection molding consists of a cycle of injection, holding pressure (cooling) and plastic parts demoulding process, so injection molding has the characteristics of periodicity. Thermoplastic injection molding has the advantages of short molding cycle, high production efficiency, small wear of melt on the mold, and large quantities of plastic parts with complex shapes, clear surface patterns and markings, and high dimensional accuracy. However, for plastic parts with large wall thickness changes, it is difficult to avoid molding defects. The anisotropy of plastic parts is also one of the quality problems, and all possible measures should be taken to minimize it.
(3) Extrusion molding
It is a molding method that makes the plastic in the viscous flow state pass through a die with a specific cross-sectional shape under high temperature and certain pressure, and then at a lower temperature, it becomes a continuous profile with the required cross-sectional shape. The production process of extrusion molding is to prepare molding materials, extrusion molding, cooling and shaping, traction and cutting, and post-extrusion treatment (quenching and tempering or heat treatment). In the extrusion molding process, pay attention to adjust the temperature of each heating section of the extruder barrel and the head die, screw revolution, traction speed and other process parameters in order to obtain qualified extrusion profiles. Particular care should be taken to adjust the rate at which the polymer melt is extruded from the head die. Because when the rate of molten material extrusion is low, the extrudate has a smooth surface and uniform cross-sectional shape; but when the molten material extrusion rate reaches a certain limit, the surface of the extrudate will become rough and lose luster, shark skin, orange peel, shape distortion and so on. When the extrusion rate is further increased, the surface of the extrudate is distorted, even branched and broken into melt fragments or cylinders. Therefore, the control of extrusion rate is very important.
(4) Injection molding
This molding method, also known as transfer molding. It is to add plastic raw materials into the preheated feeding chamber, then put the pressure column into the feeding chamber to lock the mold, apply pressure to the plastic through the pressure column, the plastic melts into a flowing state under high temperature and high pressure, and gradually solidifies into plastic parts through the gating system into the cavity. Pressure injection molding is suitable for all less than solid plastics. In principle, plastics that can be compressed and molded can also be molded by pressure injection. However, it is required that the molding material has good fluidity in the molten state when it is lower than the curing temperature, and has a large curing rate when it is higher than the curing temperature.
(5) hollow molding
Is made by extrusion or injection, is still in the plasticized state of the tubular or sheet material trend is fixed in the molding mold, immediately into the compressed air, forcing the material expansion and attached to the mold cavity wall, to be cooled and shaped after demoulding, that is, the desired hollow products of a processing method. Plastics suitable for hollow molding are high-pressure polyethylene, low-pressure polyethylene, hard polyvinyl chloride, soft polyvinyl chloride, polystyrene, polypropylene, polycarbonate, etc. According to the different methods of parison molding, hollow molding is mainly divided into extrusion blow molding and injection blow molding. The advantage of extrusion blow molding is that the structure of the extruder and the extrusion blow mold is simple, and the disadvantage is that the wall thickness of the parison is inconsistent, which is easy to cause the wall thickness of the plastic product. The advantage of injection blow molding is that the wall thickness of the parison is uniform and there is no flash. Because the injection parison has a bottom surface, the bottom of the hollow product will not produce stitching and seam, which is not only beautiful but also high in strength. The disadvantage is that the molding equipment and molds used are expensive, so this molding method is mostly used for mass production of small hollow products, and there is no extrusion blow molding method in use.
(6) die casting molding
Die casting is the abbreviation of pressure casting. The die-casting process is to add the plastic raw materials into the preheated feeding chamber, and then apply pressure to the pressure column. The plastic melts under high temperature and high pressure, and enters the cavity through the gating system of the mold, and gradually hardens and forms. This molding method is called die-casting molding, and the mold used is called die-casting molding mold. This mold is mostly used for the molding of thermosetting plastics.

Mold molding is one of the important processes for manufacturing plastic, metal and other materials. In addition, there are foam molding molds, glass fiber reinforced plastic low pressure molding molds and so on.
Mold forming can be distinguished according to different material conditions, different deformation principles, different forming machinery, forming accuracy, etc. After understanding the different forming methods, it is helpful to make good choices in the selection of manufacturing process and avoid unnecessary losses caused by wrong choices.