(1) 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 screw or plunger of the injection machine, the nozzle and the mold casting system enter the mold cavity, and the plastic is hardened and shaped into an injection mold. Products. Injection molding consists of a cycle with injection, pressure holding (cooling) and plastic part demolding process, so that injection molding has periodic characteristics. Thermoplastic injection molding has a short molding cycle, high production efficiency, and low wear of the melt to the mold. It can form large-sized plastic parts with complex shapes, clear marks and high dimensional accuracy; but for plastics with large wall thickness changes. It is difficult to avoid molding defects. Plastic anisotropy is also one of the quality issues and should be minimized by taking all possible measures. (2) Compression molding, commonly known as press molding, is one of the first methods of molding plastic parts. Compression molding is to directly add plastic to 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 having a constant shape and constant shape and size. 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, etc. It is also possible to mold and process unsaturated polyester dough (DMC), sheet molding compound (SMC), pre-formed molding compound (BMC), and the like. Under normal circumstances, the compression mold is often divided into three types: the overflow type, the non-overflow type, and the semi-overfill type according to the matching structure of the upper and lower molds of the compression film. (3) Extrusion molding is a process in which a plastic in a viscous state is passed through a die having a specific cross-sectional shape at a high temperature and a certain pressure, and then formed into a continuous profile of a desired cross-sectional shape at a lower temperature. A molding method. The extrusion molding process is to prepare molding materials, extrusion molding, cooling setting, drawing and cutting, and post-extrusion processing (tempering or heat treatment). In the extrusion molding process, pay attention to adjusting the process parameters such as the temperature of the heating section of the extruder barrel and the die of the machine head, the number of revolutions of the screw, the traction speed, etc. in order to obtain a qualified extruded profile. Particular attention should be paid to adjusting the rate at which the polymer melt is extruded from the die. Because when the rate of extrusion of the melt is low, the extrudate has a smooth surface and a uniform cross-sectional shape; however, when the extrusion rate of the molten material reaches a certain limit, the surface of the extrudate becomes rough and tarnished. , shark skin, orange peel, shape distortion and so on. As the extrusion rate is further increased, the surface of the extrudate is distorted, even fragmented and broken into melt fragments or cylinders. Therefore, the control of the extrusion rate is crucial. (4) Injection molding is also called casting molding. The plastic raw material is added into the preheating feeding chamber, and then the pressing column is placed in the feeding chamber to lock the mold, and the pressure is applied to the plastic through the pressing column, and the plastic is melted into a flowing state under high temperature and high pressure, and enters the cavity through the pouring system. Gradually solidified into plastic parts. This molding method is also called transfer molding. Injection molding is suitable for plastics that are less than solid plastics and can be compression molded in principle. They can also be formed by injection molding. However, it is required that the molding material has a good fluidity in a molten state at a temperature lower than the curing temperature, and a larger curing rate at a temperature higher than the curing temperature. (5) Hollow molding is to fix the tubular or sheet-like blank material which is still in plasticized state by extrusion or injection into the molding die, and immediately introduces compressed air to force the material to expand and stick to the mold type. On the wall surface of the cavity, after being cooled and shaped, the mold is released, that is, a processing method of the desired hollow product is obtained. Plastics suitable for hollow molding are high pressure polyethylene, low pressure polyethylene, hard polyvinyl chloride, soft polyvinyl chloride, polystyrene, polypropylene, polycarbonate, and the like. According to the different molding methods of the parison, the hollow molding is mainly divided into two types: extrusion blow molding hollow molding and injection blow molding hollow molding. The advantage of the extrusion blow molding hollow molding is that the structure of the extruder and the extrusion blow molding mold is simple, and the disadvantage is that the wall thickness of the parison is inconsistent, and the wall thickness of the plastic product is likely to be uneven. The picture on the right is a schematic diagram of the extrusion blow molding hollow molding principle. The advantage of injection blow molding is that the parison has a uniform wall thickness and no flash. Since the injection parison has a bottom surface, the bottom of the hollow product does not have a seam and a seam, which is not only beautiful but also high in strength. The disadvantage is that the molding equipment and the mold used are expensive, so this molding method is mostly used for mass production of small hollow products, and there is no extensive extrusion blow molding method in use. (6) Die-casting mold The die-casting mold is also called transfer molding mold. The plastic raw material is added to the preheating feeding chamber, and then the pressure is applied to the pressing column. The plastic is melted under high temperature and high pressure, and enters the cavity through the casting system of the mold, and is gradually hardened. This molding method is called die casting molding, and the mold used is used. Called die casting mold. This type of mold is mostly used for the molding of thermosetting plastics. In addition, there are foam molding dies, glass fiber reinforced plastic low pressure molding dies and so on.