The molding processing methods of plastic products for household appliances mainly include injection molding, extrusion molding, thermoforming, hollow molding, laminate molding, compression molding, transfer molding, foam molding, pouring molding, inlay casting, sealing casting, etc., among which injection molding is the main method.
In recent years, some new plastic processing technologies and new equipment have been widely used in the molding of household appliances plastic products, such as precision injection molding, rapid prototyping technology, melt core injection molding technology, air-assisted/water-assisted injection molding technology, electromagnetic dynamic injection molding technology and film injection molding technology.
1. Precision injection molding
The can products have high precision and high repeatability in terms of size and weight. The injection molding machine using this technology can achieve high pressure and high speed injection. Because the control mode is usually open-loop or closed-loop control, the injection molding process parameters can be controlled with high precision.
Usually, precision injection molding requires high accuracy of the mold. At present, domestic has been able to produce small and medium-sized precision injection molding machines.
2. Rapid prototyping technology
It is developed rapidly along with the development of household appliance varieties to the direction of diversification and continuous renewal. It is mainly used to prepare plastic shells for household appliances. The advantage of this technology is that small batch production of plastic parts can be achieved without molds.
At present, the relatively mature rapid prototyping methods include laser scanning prototyping and liquid light curing prototyping, among which laser scanning prototyping is widely used. The laser scanning equipment is composed of a laser light source, a scanning device, a dusting device and a computer. The processing process is, by the computer control of the laser head according to a certain trajectory to scan, in the laser through the position, plastic powder melting and bonded together, every scanning, micro-powder device sprinkled a layer of thin powder, so that after repeated scanning, formed a certain shape and size of the product.
Now, some domestic enterprises have been able to produce laser scanning molding machine and plastic powder, but the performance of the equipment is not stable, and the variety of powder is less.
3. Melting core injection technology
It is usually used to form special cavity products which require high roughness and accuracy of cavity and can not be processed by hollow forming or rotary forming method.
At present, the application of this technology has been relatively mature abroad, but it is still in individual application in China. The processing principle of the technology is that the core of the cavity is formed first, and then the core is used as an insert for injection molding.
Under the heating effect of the injection molding part, the core mold melts and flows out, thus forming a cavity. It is important to master the melting point of core materials and plastic parts when using this technology. Generally, the core material can be selected according to the specific circumstances of the general plastic, thermoplastic elastoplast or low melting point metals such as lead, tin, etc.
4. Air/water injection molding
Widely used, can be molded into a variety of types of injection parts, the typical product is TV shell. During injection molding, gas or superheated water can be injected into the cavity almost synchronously with the plastic melt.
At this time, the plastic melt will be covered with gas or hot water, and the molded plastic products are sandwich structures. After the plastic parts are shaped, the gas or water can be released. This kind of product has the advantages of saving material, shrinking, good appearance and good rigidity. The key part of the molding equipment is the gas-assisted or water-assisted device and its control software.
In recent years, although there are many studies on this topic and the application speed is fast in China, the domestic equipment is still unstable.
5. Electromagnetic dynamic injection molding technology
This technique causes the screw to vibrate reciprocally in the axial direction by the action of electromagnetic force. Because the plastic can be micro-plasticized in the pre-plasticization stage, so that the plastic structure of the press-holding stage is more compact, and the internal stress of the product is reduced.
This technique can be used to form more demanding products such as optical discs. When used in the molding of common products, it can improve the quality of products.
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6. Film injection molding technology
When using this technology, it is necessary to clip the special printed decorative plastic film in the mold before injection molding, and then injection molding. The printing film can be attached to the surface of plastic parts after heat deformation, which is not only beautiful and firm, but also saves the decoration step.
Generally, the demand for plastic molds for household appliances plastic products is very large, for example, a refrigerator or a fully automatic washing machine usually needs more than 100 pairs of plastic molds, an air conditioner needs more than 20 pairs, a color TV needs 50-70 pairs of plastic molds.
At the same time, the technical requirements for plastic molds are relatively high, and the processing cycle of molds 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 molds and laminate injection molds are gradually increasing in China.
