Molding Classification of Molds

- Oct 24, 2017-

(1) Injection Molding

is to add plastic to the injection machine in the heating cylinder, plastic melting melt, in the injection machine screw or plunger push, through the nozzle and mold gating system into the mold cavity, due to physical and chemical effects hardened into injection molding products. Injection molding is formed by injection, holding pressure (cooling) and plastic parts stripping process of the cycle period, so injection molding has a cyclical characteristics. The molding cycle of thermoplastic injection molding is short, the production efficiency is high, the melt is small to die, it can form complex shape, the surface pattern and the mark is clear, the dimension precision is high, but the plastic parts with large change of wall thickness are difficult to avoid forming defects. Plastic parts anisotropy is also one of the quality problems, should be used all possible measures to minimize.

(2) Compression molding

Commonly known as pressing molding, is one of the first methods of forming plastic parts. Compression molding is to add plastic directly to a certain temperature open mold cavity, and then closed the mold, under the action of heat and pressure plastic melt into a flow state. As a result of physical and chemical action, the plastic hardened into a certain shape and size of the normal temperature unchanged plastic parts. Compression molding is mainly used for molding thermosetting plastics, such as phenolic molding powder, urea aldehyde and melamine formaldehyde molding powder, glass fiber reinforced bakelite, epoxy resin, DAP resin, silicone resin, polyimide and other molding plastic, but also can be formed to process unsaturated polyester pellet (DMC), flake molding plastic (SMC), Precast Monolithic Moulding Plastics (BMC), etc. In general, the compression module is divided into three types: overflow type, overflow type, and semi-overflow type.

(3) Extrusion Molding

is to make the plastic in the state of viscous flow, under the high temperature and certain pressure, through a specific section shape of the mouth mold, and then at a lower temperature, the shape of the desired cross-section of the continuous profile of a molding method. Extrusion molding process, is the preparation of molding materials, extrusion molding, cooling stereotypes, traction and cutting, extrusion products after treatment (quenching or heat treatment). During the extrusion molding process, attention is paid to adjust the temperature of each heating section and die of the extruder barrel, the screw number, the speed of traction and so on to get the qualified extruded profile. Special attention should be paid to the adjustment of polymer melts by the die in the head of the rate of extrusion. Because when the melt extrusion rate is low, the extrusion has a smooth surface, uniform cross-section shape; But when the melting material extrusion rate reaches a certain limit, the extruded surface becomes coarse, loses luster, appears shark skin, the orange skin pattern, the shape distortion and so on phenomenon. When the extrusion rate increases further, the surface of the extruded material appears distorted, even fragmented and fractured into melt fragments or columns. Therefore, the control of extrusion rate is very important.

(4) Pressure injection molding

Also known as casting pressure molding. is to add the plastic raw materials to preheat the feeding room, and then put the pressure column into the feeding chamber locking mold, through the pressure column to plastic pressure, plastic at high temperature, high-pressure melting into the flow state, and through the pouring system into the cavity gradually solidified into plastic parts. This kind of molding method, also known as transfer molding. Pressure injection molding is suitable for each less than the solid plastic, in principle, can be compressed molding plastic, but also can be molded by pressure injection. However, when the molding material is lower than the curing temperature, the molten state has a good fluidity and has a larger curing rate than the curing temperature.

(5) Hollow forming

is made by extrusion or injection, still in the plastic state of the tubular or sheet-shaped slab trend fixed in the molding mold, immediately through compressed air, forcing the expansion of the billet and affixed to the mold cavity wall surface, to be cooled after the setting demoulding, that is, the need for a processing method of hollow products. Suitable for the hollow molding of plastic for high-pressure polyethylene, low pressure polyethylene, hard polyvinyl chloride, soft PVC, polystyrene, polypropylene, polycarbonate and so on. According to the different forming method of Parison, hollow forming is divided into two kinds: extrusion blow molding hollow forming and injection blow molding hollow forming. The advantage of extrusion blow molding is that the structure of extruder and extrusion blow moulding die is simple, the defect is that the wall thickness of parison is inconsistent, and the wall thickness of plastic products is not uniform. The right picture is the schematic diagram of extrusion blow molding hollow forming. The advantages of injection blow molding hollow forming are that the wall thickness of the parison is uniform and no flying edge, because the bottom surface of the injection parison is not produced, so it is not only beautiful but also high strength. The disadvantage is the use of molding equipment and mold price expensive, so this molding method is used for large-scale production of small hollow products on the use of no extrusion blow molding hollow forming method is extensive.

(6) Die casting mould

Die-casting mold also known as transfer molding mold. The plastic raw materials into the preheating of the feeding room, and then pressure column, plastic at high temperature and pressure melting, and through the mold pouring system into the cavity, gradually hardened molding, this molding method called die-casting type, the mold used is called die-casting mold. This mold is used for molding thermosetting plastics.