The molding methods of plastic products for home appliances mainly include injection molding, extrusion molding, hot forming, hollow molding, laminating, compression molding, transfer molding, foam molding, pouring molding, inlay casting and sealing casting, among which injection molding is the main form.
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In recent years, some new plastic processing technologies and equipment have been widely used in the molding of home appliances plastic products, such as precision injection molding, rapid prototyping technology, fusible core injection molding technology, gas assisted / water assisted injection molding technology, electromagnetic dynamic injection molding technology and film covered injection molding technology.
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1. Precision injection
It can ensure that the products have high precision and repeatability in size and weight. The injection machine with this technology can realize high pressure and high speed injection. Because its control mode is usually open-loop or closed-loop control, it can achieve high-precision control of injection molding process parameters.
Generally, precision injection requires high precision of mold. At present, China has been able to produce small and medium-sized precision injection molding machines.
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2. Rapid prototyping technology
With the development of the variety of home appliances and the continuous upgrading, it has developed rapidly. It is mainly used to prepare the plastic shell for home appliances. The advantage of this technology is that the small batch production of plastic parts can be realized without mould.
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At present, the more mature rapid prototyping methods are laser scanning molding and liquid light curing molding, among which laser scanning molding is widely used. Laser scanning equipment is composed of laser light source, scanning device, dusting device and computer. The processing process is that the laser head controlled by the computer scans according to a certain path. At the position where the laser passes, the plastic micro powder is heated, melted and bonded together. After each scanning, the micro powder device sprinkles a layer of thin powder. In this way, after repeated scanning, a product with a certain shape and size is formed.
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At present, some domestic enterprises have been able to produce laser scanning molding machine and plastic micro powder, but the performance of the equipment is not stable, and the varieties and brands of micro powder are few.
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3. Fusible core injection technology
It is usually used to form special-shaped cavity products with high requirements for cavity roughness and accuracy, which can not be processed by hollow forming or rotary forming.
At present, the application of this technology in foreign countries has been relatively mature, but it is still in the state of individual application in China. The processing principle of the technology is to form the core of the cavity first, and then use the core as the insert for injection molding.
Under the heating action of the injection molding part, the core mold melts and flows out, thus forming a cavity. The most important point of using this technology is to master the melting point of core materials and plastic parts. Generally, the core material can be general plastic, thermoplastic elastomer or low melting point metal such as lead, tin and so on.
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4. Gas assisted / water assisted injection molding
The utility model has a wide range of uses and can form various types of injection molded parts, and the typical product is a TV shell. During injection molding, gas or superheated water can be injected into the mold cavity almost synchronously with the plastic melt.
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At this time, the plastic melt will cover the gas or superheated water. The plastic products formed are sandwich structures. After the plastic parts are finalized, the gas or water can be discharged to demould. Such products have the advantages of material saving, small shrinkage, good appearance and good rigidity. The key part of forming equipment is gas assisted or water assisted device and its control software.
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In recent years, although there are many researches and application speed in China, domestic equipment is not stable.
5. Electromagnetic dynamic injection molding technology
This technology makes the screw produce reciprocating vibration in the axial direction by the action of electromagnetic force. Because the plastic can be micro plasticized in the pre plasticizing stage, the structure of the plastic part in the pressure maintaining stage is more compact, and the internal stress of the product is reduced.
This technology can be used to form products with high requirements, such as optical disk. When it is used for the forming of common products, the quality of products can be improved.
6. Film covered injection molding technology
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When using the technology, the special printing decorative plastic film needs to be clamped in the mold before injection molding, and then injection molding. After heat deformation, the printing film can fit on the surface of plastic parts, which is not only beautiful and firm, but also saves the post decoration steps.
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In general, the demand for plastic molds for household appliances plastic products is very large. For example, a refrigerator or a full-automatic washing machine usually needs more than 100 plastic molds, an air conditioner needs more than 20, and a color TV needs 50-70 plastic molds.
At the same time, the technical requirements of plastic mold are relatively high, and the processing cycle of mold is often required to be as short as possible, which greatly promotes the development of mold design and modern mold manufacturing technology. In addition, some difficult molds such as hot runner injection mold and laminated injection mold are gradually increasing in China.
