The molding and processing methods of plastic products for household appliances mainly include injection molding, extrusion molding, thermoforming, hollow molding, lamination molding, compression molding, transfer molding, foam plastic molding, pouring molding, embedding casting, sealing casting, etc., among which injection molding is the main one.
In recent years, some new plastic processing technologies and new equipment have been widely used in the molding of household appliance plastic products, such as precision injection molding, rapid prototyping technology, melt core injection molding technology, gas-assisted/water-assisted injection molding technology, electromagnetic dynamic injection molding technology and laminated injection molding technology.
1. Precision injection molding
It can ensure that the products have high precision and high repeatability in terms of size and weight. Injection molding machines with this technology can achieve high-pressure, high-speed injection. Since the control mode is usually open-loop or closed-loop, high-precision control of injection molding process parameters can be achieved.
In general, precision injection molding requires high precision of the mold. At present, China has been able to produce small and medium-sized precision injection molding machines.
2. Rapid prototyping technology
It is developed rapidly with the diversification of household appliances and continuous upgrading, and is mainly used for the preparation of plastic shells for household appliances. The advantage of this technology is that small batches of plastic parts can be produced without the need for molds.
At present, the more mature rapid prototyping methods include laser scanning molding and liquid light curing molding, among which laser scanning molding method 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 that the laser head controlled by the computer scans according to a certain trajectory, and at the position where the laser passes, the plastic powder is heated and melted and bonded together, and after each scanning, the powder device sprinkles a layer of thin powder, so that after repeated scanning, a product with a certain shape and size is formed.
At present, there are some domestic enterprises that can produce laser scanning molding machines and plastic powder, but the performance of the equipment is unstable, and the varieties and grades of the powder are also few.
3. Fused core injection molding technology
It is usually used to form special-shaped cavity products that require high cavity roughness and accuracy and cannot be processed by hollow molding or rotational molding methods.
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 this technology is to first mold the core shape that makes up the cavity, and then use the core shape as an insert injection molding.
Under the heating action of the injection molded part, the core melts and flows out, thus forming a cavity. The most important point of using this technology is to know the melting point of the core material and the plastic part. In general, core materials can be general-purpose plastics, thermoplastic elastomers or low-melting metals such as lead, tin, etc., depending on the specific situation.
4. Gas-assisted/water-assisted injection molding
It is widely used and can be molded into many types of injection molded parts, the typical product of which is the TV housing. During injection molding, gas or superheated water can be injected into the cavity almost simultaneously with the plastic melt.
At this time, the plastic melt will be coated with gas or superheated water, and the molded plastic products are sandwich structures, and the gas or water can be discharged after the plastic parts are finalized. This kind of product has the advantages of material saving, small shrinkage, good appearance and good rigidity. The key part of the molding equipment is the gas-assisted or water-assisted unit