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The working principle of the injection molding machine

June 27, 2022

The working principle of the injection molding machine


The working principle of the injection molding machine is similar to that of a syringe for injection. It uses the thrust of the screw (or plunger) to inject the plasticized plastic in the molten state (that is, the viscous state) into the closed mold cavity. The process of obtaining products after curing and shaping.
Injection molding is a cycle process, each cycle mainly includes: quantitative feeding - melt plasticization - pressure injection - mold filling and cooling - mold opening and taking out. After the plastic parts are taken out, the mold is closed again for the next cycle.
Injection molding machine operation items: injection molding machine operation items include control keyboard operation, electrical control system operation and hydraulic system operation. The selection of injection process action, feeding action, injection pressure, injection speed, ejection type, temperature monitoring of each section of the barrel, adjustment of injection pressure and back pressure, etc. are carried out respectively.
The general molding process of the screw injection molding machine is as follows: first, the granular or powdery plastic is added into the barrel, and the plastic is melted by the rotation of the screw and the heating of the outer wall of the barrel, and then the machine is closed and the injection seat is moved forward. Make the nozzle close to the gate of the mold, and then inject pressure oil into the injection cylinder to advance the screw, so that the molten material is injected into the closed mold with low temperature at a high pressure and a fast speed. Time and pressure are maintained (also known as pressure holding), cooled to solidify and form, and then the mold can be opened and the product can be taken out (the purpose of pressure holding is to prevent the backflow of the melt in the mold cavity, replenish the material into the mold cavity, and ensure the product. with certain density and dimensional tolerances). The basic requirements of injection molding are plasticizing, injection and molding. Plasticization is the premise to realize and ensure the quality of molded products, and in order to meet the requirements of molding, injection must ensure sufficient pressure and speed. At the same time, due to the high injection pressure, a correspondingly high pressure is generated in the mold cavity (the average pressure in the mold cavity is generally between 20 and 45MPa), so there must be a sufficient clamping force. It can be seen that the injection device and the clamping device are the key components of the injection molding machine.
There are three main aspects to the evaluation of plastic products, the first is the appearance quality, including integrity, color, gloss, etc.; the second is the accuracy of size and relative position; the third is the physical properties, chemical properties, electrical properties, etc. These quality requirements are also different according to the different occasions where the products are used. The defects of the product mainly lie in the design of the mold, the manufacturing accuracy and the degree of wear. But in fact, technicians in plastic processing plants often suffer from the difficult situation of using technological means to make up for the problems caused by mold defects and have little effect.
The adjustment of the process in the production process is a necessary way to improve the quality and output of the product. Because the injection molding cycle itself is very short, if the process conditions are not well mastered, there will be an endless stream of waste products. When adjusting the process, it is best to change only one condition at a time and observe it several times. If the pressure, temperature and time are all adjusted together, it is easy to cause confusion and misunderstanding, and there is no reason for the problem. There are various measures and means to adjust the process. For example, there are more than ten possible solutions to solve the problem of dissatisfaction with products. Only by choosing one or two main solutions to solve the crux of the problem can the problem be truly solved. In addition, attention should be paid to the dialectical relationship in the solution. For example, if the product is dented, sometimes the material temperature should be increased, and sometimes the material temperature should be reduced; sometimes the material quantity should be increased, and sometimes the material quantity should be reduced. Recognize the feasibility of reverse measures to solve the problem.

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