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Share The Various Types Of Molds
May 18, 2018

It's a thing of life. It's a variety of things. It's beautiful, and these are all made using molds. The various molds are the tools used to shape things. There are many types of molds, which can be divided into different types. If they are divided according to the type of molding, they can be divided into the following types of molds.

(1) injection molding

The plastic is first added to the heating barrel of the injection machine. The plastic is melted by heat and pushed into the mold cavity by the nozzle and the mold casting system under the push of the injection screw or the plunger. Due to the physical and chemical effects, it is hardened and shaped into an injection molding. Products. Injection molding has a cyclical cycle consisting of injection, holding pressure (cooling), and demolding of plastic parts, so injection molding is characterized by periodicity. Thermoplastic injection molding has a short molding cycle, high production efficiency, and low wear of the melt on the mold. It can form large quantities of plastic parts with complex shapes, clear surface patterns and markings, and high dimensional accuracy; however, it has a large variation in wall thickness. It is difficult to avoid molding defects. The anisotropy of plastic parts is also one of the quality issues. All possible measures should be adopted to minimize them.

(2) Compression molding

Commonly called press molding is one of the first methods of molding plastic parts. Compression molding is to add plastic directly to an open mold cavity with a certain temperature, and then close the mold, and the plastic melts into a flowing state under the effect of heat and pressure. Due to the physical and chemical effects, the plastic hardens into a plastic part having 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. It can also process unsaturated polyester dough (DMC), sheet molding compound (SMC), and prefabricated integral molding compound (BMC). Under normal circumstances, the compression mold is often divided into three types: overflow type, non-overflow type, and semi-overflow type according to the matching structure of the upper and lower molds of the compression membrane.

(3) Extrusion molding

It is a molding method to make a plastic in a viscous flow state, at a high temperature and under a certain pressure, through a die having a specific cross-sectional shape, and then, at a lower temperature, to shape a continuous section having a desired cross-sectional shape. Extrusion molding production process is to prepare molding materials, extrusion molding, cooling and setting, traction and cutting, post-processing of extrusion products (conditioning or heat treatment). During the extrusion molding process, attention is paid to adjusting the process parameters such as temperature, screw rotation number, and traction speed of each heating section and head mold of the extruder barrel so as to obtain a qualified extrusion profile. Special attention should be paid to adjusting the rate of polymer melt extrusion from the die. Because when the melt extrusion rate is low, the extrudate has a smooth surface and a uniform cross-sectional shape; but when the molten material extrusion rate reaches a certain limit, the surface of the extrudate will become rough and tarnish. , Sharkskin, orange peel, shape distortion and so on. When the extrusion rate is further increased, the surface of the extrudate is distorted and even splits and breaks into melt chips or cylinders. Therefore, the control of the extrusion rate is very important.

(4) Injection molding

Also known as cast molding. The plastic raw material is added to the preheated feed chamber, and then the pressure column is placed in the feed chamber to lock the mold, and the pressure is applied to the plastic through the press column. The plastic melts at a high temperature and high pressure to flow and enters the cavity through the pouring system. Gradually cured into plastic parts. This molding method is also called transfer molding. Pressure injection molding is applicable to plastics that are lower than solid plastics, and can in principle be compression molded, and can also be formed by injection molding. However, when the molding material is lower than the curing temperature, the molten state has good fluidity, and when it is higher than the curing temperature, it has a larger curing rate.

(5) Blow molding

The tendency is to fix the tubular or sheet stock material, which is still in the plasticized state, produced by extrusion or injection, in the molding die, and immediately introduce compressed air to force the billet to expand and stick to the wall of the cavity of the mold. After cooling, the mold is demoulded to obtain a desired processing method for the hollow products. Suitable plastics for hollow molding are high-pressure polyethylene, low-pressure polyethylene, rigid polyvinyl chloride, soft polyvinyl chloride, polystyrene, polypropylene, and polycarbonate. According to the different forming methods of the blank, the hollow forming can be mainly divided into two types: 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. 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 figure on the right shows the principle of extrusion blow molding. Injection blow molding has the advantages of uniform wall thickness of the parison and no flash. Since the injection parison has a bottom surface, the bottom of the hollow product will not have cracks and seams, which is not only aesthetic 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 the mass production of small hollow products, and there is no extrusion blow molding in the use of a wide range of molding methods.

(6) Die Casting Mould

Die casting mold, also known as transfer molding die. The plastic raw material is added into the preheating feed chamber, and then pressure is applied to the pressurizing column. The plastic melts under high temperature and high pressure, and enters the cavity through the casting system of the mold, gradually hardening forming, this molding method is called die casting molding, the used mold Die casting mold. This type of mold is mostly used for molding thermosetting plastics.

In addition, there are foam molding molds, glass fiber reinforced plastic low pressure molding molds and so on. If you want to learn more about the mold, please continue to pay attention to our official website.