Plastic mold plays a very important role in plastic processing. The level of mold design and manufacturing capacity also reflects the industrial level of a country. In recent years, the output and level of plastic mold have been developing rapidly. The proportion of molds with high efficiency, automation, large-scale, precision and long life is increasing. From mold design, processing methods, processing equipment, table Surface treatment and other aspects to summarize the development status of the mold.

Plastic forming method and mold design

Gas assisted molding, gas assisted molding is not a new technology, but in recent years, it develops rapidly and some new methods appear. The auxiliary injection of liquefied gas is to inject a kind of preheat special gasified liquid from the injection into the plastic melt. When the liquid is heated in the mold cavity, it is vaporized and expanded, making it hollow, and pushing the melt to the surface of the mold cavity. This method can be used for any thermoplastic. Vibration gas assisted injection is to apply vibration energy to the plastic melt by vibrating the compressed gas of the product, so as to control the microstructure of the product and improve the performance of the product. Some manufacturers convert the gas used in the gas assisted injection to produce thinner products, or large hollow products, with higher quality and lower cost, but the key point is the leakage of water,

In push-pull mold, two or more channels are set around the mold cavity and connected with two or more injection devices or reciprocating pistons. Before the melt solidifies after injection, the screw or piston of the injection device moves the melt in the reciprocating push-pull mold cavity back and forth. This technology is called dynamic pressure maintaining technology. Its purpose is to avoid forming thick products with traditional molding methods There will be a big shrinkage problem. High pressure molding thin shell products, thin shell products are generally products with a long process ratio, mostly using multi-point gate mold, but multi-point pouring will cause fusion joint, which will affect the visual effect of some transparent products. Single point pouring is not easy to fill the mold cavity, so high pressure molding technology can be used for molding, such as the U.S. air force, F16 war The cockpit of the machine is produced by this technology. At present, this technology has been used to produce PC automobile windshield. The injection pressure of high-pressure molding is generally more than 200MPa, so the mold material should also be high-strength and rigid with high Young's modulus. The key of high-pressure molding is the control of mold temperature. In addition, the exhaust of the mold cavity must be smooth. Otherwise, due to high-speed injection, poor exhaust will scorch the plastic.

Hot runner die: more and more hot runner technology is used in multi cavity die, and its dynamic cutting technology is a bright spot in die technology. That is to say, by adjusting the flow of plastic through a needle valve, the injection time, injection pressure and other parameters can be set for each gate respectively, so as to obtain balance and injection and the best quality assurance. The needle valve can move dynamically and steplessly through the hydraulic driving piston, and the position of the needle valve determines the injection flow and pressure. There is a pressure sensor in the channel, which can continuously record the pressure in the channel, and then control the needle valve position and adjust the melt pressure.

Mold for fusible core injection molding: this method is to put the fusible core made of low melting point alloy into the mold as a inlay for injection molding. Then, the product containing the fusible core is heated to remove the fusible core. The forming method is used for products with complex hollow shapes, such as the oil pipe or the air pipe of the automobile and other hollow plastic parts with complex shapes. The products formed by this kind of mould include: tennis racket handle, automobile water pump, centrifugal hot water pump, spacecraft oil pump, etc,

Injection / compression molding mold: injection / compression molding can produce low stress. For products with good optical properties, the technological process is as follows: mold closing (but the dynamic and fixed mold are not completely closed, leaving a gap for later compression), injection of melt, secondary mold closing (that is, compression makes the melt be compacted in the mold), cooling, mold opening and demoulding. In the mold design, we should pay attention to the fact that the mold is not fully closed at the beginning of closing, so in order to prevent overflow during injection, we should design the structure to prevent overflow in the mold,

Laminating mold: multiple cavities are arranged in the closing square, instead of in the same plane, which can give full play to the plasticizing ability of the injection machine. This kind of mold is generally used in the hot runner mold, which can greatly improve the efficiency,

Injection mold for layered products: injection mold for layered products has the characteristics of coextrusion and injection molding. It can realize the multi-layer combination of different materials with any thickness on the products. The thickness of each layer can be as small as 0.1-10 mm, and the number of layers can reach thousands. This kind of mold is actually a combination of an injection mold and a multi-stage coextrusion mold.

DSi: this method can form hollow products or composite products of various materials. The process is: close the mold (for hollow products, at this time, the two half cavities are in different positions), inject separately, move the mold to the two half cavities, and inject resin combining the two halves cavities in the middle. Compared with blow molded products, the products formed by this method have It has the advantages of good surface accuracy, high dimensional accuracy, uniform wall thickness and large design freedom.

Aluminum mold: an outstanding point in plastic manufacturing technology is the application of aluminum alloy materials. The service life of aluminum alloy plastic mold developed by Corus company can reach more than 300000. Pechiney rhenalu company uses its mi-600 aluminum material to manufacture plastic, with the service life reaching more than 500000 times

Mould manufacturing

High speed milling: at present, high speed cutting has entered the field of precision machining, its positioning accuracy has been improved to {+ 25um}, using liquid