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Process requirements for injection molding

Release time:2023-08-16

Injection molding is a specific cycle. There are five factors that affect injection molding: temperature, speed, pressure, position and time. These five process factors determine the quality of injection molding. The quality problems often encountered in injection molding are mostly caused by five uncontrolled quality abnormalities.


Temperature is the primary factor of injection molding, which can be divided into several key factors, such as drying temperature, material temperature and mold temperature. The drying temperature is the pre drying of plastic materials to ensure that the molding quality and the drying and wetting degree of plastic are within a certain range; Temperature is the normal plasticization and smooth filling and molding of plastics; Mold temperature is an important factor in the process of injection molding. The temperature, appearance and molding cycle of injection mold affect the cooling rate and appearance quality of products in the mold cavity.


The second factor is speed: speed is divided into injection mold speed, molten material temperature, demoulding speed, mold opening and closing speed, and mold advance and retreat speed before thimble. The increase of injection speed affects the increase of mold pressure. Improving the injection molding speed can improve the flow rate, make the product quality uniform, and ensure the product quality. High speed injection is suitable for long process products. The injection speed of controlling the product size at low speed affects the plasticizing ability. Plasticizing ability is an important parameter of plasticizing quality. The higher the speed is, the higher the melt temperature is, and the loosening speed with stronger plasticizing ability is to reduce the melt specific volume, The opening and closing speed of reducing the internal pressure of the melt and preventing its outflow is an important condition to ensure the mechanical operation.


The third factor is pressure: pressure is divided into injection pressure, holding pressure, back pressure, mold locking pressure, mold support protection pressure and ejection pressure. Injection pressure is used to ensure the pressure loss of melt from nozzle runner gate cavity to ensure that the cavity is full; The pressure maintaining method is used to reduce the cracking or bending of the plastic mold caused by excessive injection pressure. The pressed method is used to prevent the mold from cracking due to foreign matters under high speed and high pressure; The jacking method is used to prevent the product from detaching from the mold surface and damaging the mold.


The fourth factor is location: location can be divided into mold opening location, ejection modulus, measurement modulus, injection modulus and buffer modulus. The mold opening position is to ensure that the demoulding parts can work normally; The ejection stroke is the protective effect of the partial return of the spring on the ejection limit; The jacking stroke is to ensure that there are enough plastic filling molds to ensure product quality; The top return process is to increase the specific capacity of the melt in the metering cavity, reduce the internal pressure, and prevent the melt from flowing outward from the cavity; The jacking stroke is to prevent mechanical damage accidents caused by the contact between the screw head and the nozzle.


The fifth factor is time: time is divided into cooling time of plastic products, plastisol time, plastic drying time, cooling time of plastic products, melting time, drying time, circulation time and pressure holding time. The molding of products requires a specific cycle; Injection time determines the size of injection molded products; Pressure maintaining is to prevent melt backflow; Cooling shrinkage effect; The cooling time is to ensure the solidification of plastic products and prevent product deformation; The spraying time is to ensure sufficient products; Drying time is a factor to ensure that the product will not grow longer and the quality is poor.


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