What kinds of molds are there?

basic classification according to the different materials, molds can be divided into metal molds and non-metal molds. Metal molds are divided into: casting molds (non-ferrous metal die casting, steel casting), stamping molds and forging molds; Non-metallic molds are also divided into: plastic molds and inorganic non-metallic molds. According to the different materials of the mold itself, the mold can be divided into: sand mold, metal mold, vacuum mold, paraffin mold and so on. Among them, with the rapid development of polymer plastics, plastic molds are closely related to people's lives. Plastic molds can generally be divided into: injection molding mold, extrusion molding mold, gas-assisted molding mold and so on. Large-scale production of non-sheet metal steel parts-cold heading, die forging, metal die, etc. Sheet metal discharging-hot rolling, cold rolling, hot rolling, cold rolling sheet metal processing-drawing, shaping, bending, punching, blanking non-ferrous metals-die casting, powder metallurgy plastic parts-injection molding, blow molding (plastic bottles), extrusion (pipe fittings) molds Other categories: alloy molds, sheet metal molds, plastic molds, stamping molds, rubber molds, Classification of casting mold, forging mold, extrusion mold, die casting mold, automobile mold and wire rolling mold (1) Two-plate mold: also known as single parting surface mold, is the simplest type of injection mold, which divides the whole mold into two parts with parting surface as the interface: moving mold and fixed mold. Part of the cavity is in the moving mold, and the other part is in the fixed mold. The main runner is in the fixed mold; The runner is set on the parting surface. After the mold is opened, the product and runner are left in the moving mold, and the moving mold part is provided with an ejection system. (2) Three-plate mold or fine nozzle mold: There are two parting surfaces to divide the mold into three parts, and the sprue plate is increased compared with the two plates, which is suitable for occasions where there are no sprue marks around the product. This mold is divided into point gates, so it is called fine nozzle mold, and the structure of this mold is correspondingly more complicated. Start the power with a mountain screw or pull plate. Classification of molding (1) Injection molding: firstly, plastic is added into the heating barrel of the injection machine, which is heated and melted, pushed by the screw or plunger of the injection machine, enters the mold cavity through the nozzle and mold gating system, and hardens and shapes into injection products due to physical and chemical effects. Injection molding consists of injection, pressure holding (cooling) and plastic parts demoulding, so injection molding has the characteristics of periodicity. Thermoplastic injection molding has the advantages of short molding cycle, high production efficiency, little wear of molten materials on molds, and large-scale molding of plastic parts with complex shapes, clear surface patterns and marks and high dimensional accuracy; However, it is difficult to avoid molding defects for plastic parts with large wall thickness changes. Anisotropy of plastic parts is also one of the quality problems, and all possible measures should be taken to minimize it. (2) Compression molding: commonly known as compression molding, it is one of the earliest methods of molding plastic parts. Compression molding is to directly add plastic into an open mold cavity with a certain temperature, 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 hardens into a plastic part with a certain shape and size that remains unchanged at room temperature. Compression molding is mainly used to mold thermosetting plastics, such as phenolic molding powder, urea-formaldehyde and melamine-formaldehyde molding powder, glass fiber reinforced phenolic plastics, epoxy resin, DAP resin, silicone resin, polyimide, etc. It can also be used to mold unsaturated polyester dough (DMC), sheet molding compound (SMC), prefabricated integral molding compound (BMC), etc. In general, according to the matching structure of the upper and lower dies of the compression film, the compression dies are divided into three types: overflow type, non-overflow type and semi-overflow type. (3) Extrusion molding: It is a molding method that makes the plastic in a viscous state pass through a die with a specific cross-sectional shape at a high temperature and a certain pressure, and then it is shaped into a continuous profile with the required cross-sectional shape at a lower temperature. The production process of extrusion molding is preparing molding materials, extrusion molding, cooling and setting, traction and cutting, and post-treatment (quenching and tempering or heat treatment) of extruded products. In the process of extrusion molding, we should pay attention to adjust the process parameters such as the temperature of each heating section of extruder barrel and die, the number of screw revolutions, and the traction speed to get qualified extrusion profiles. Special attention should be paid to adjusting the extrusion rate of polymer melt from the die. Because when the extrusion rate of melt is low, the extrudate has a smooth surface and a uniform cross-sectional shape; However, when the extrusion rate of molten materials reaches a certain limit, the surface of the extrudate will become rough and lose luster, and shark skin, orange skin lines, shape distortion and other phenomena will appear. When 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 extrusion rate is very important. (4) Injection molding: also known as casting molding. The method comprises the following steps: adding plastic raw materials into a preheated feeding chamber, then putting a pressing column into the feeding chamber to lock the mold, exerting pressure on the plastic through the pressing column, melting the plastic into a flowing state at high temperature and high pressure, and gradually solidifying the plastic into a plastic part through a pouring system. This molding method is also called transfer molding. Injection molding is suitable for plastics that are lower than solid plastics and can be compression molded in principle, and can also be molded by injection molding. However, it is required that the molding material has good fluidity in the molten state when it is below the curing temperature, and has a large curing rate when it is above the curing temperature. (5) Hollow molding: it is a processing method that the tubular or flaky blank made by extrusion or injection and still in the plasticizing state is fixed in the molding die, and compressed air is immediately introduced to force the blank to expand and stick to the wall of the mold cavity, and then the required hollow product is obtained by demoulding after cooling and setting. Plastics suitable for hollow molding are high pressure polyethylene, low pressure polyethylene, hard PVC, soft PVC, polystyrene, polypropylene, polycarbonate and so on. According to the different parison molding methods, hollow molding can be divided into two types: extrusion blow molding and injection blow molding. The advantage of extrusion blow molding is that the structure of extruder and extrusion blow mold is simple, but the disadvantage is that the wall thickness of parison is inconsistent, which easily leads to uneven wall thickness of plastic products. The picture on the right is a schematic diagram of the principle of extrusion blow molding. The advantage of injection blow molding hollow molding is that the wall thickness of parison is uniform and there is no flash. Because the injection parison has a bottom surface, the bottom of the hollow product will not be spliced and stitched, which is not only beautiful but also beautiful.