The Working Principle of Injection Molding Machine

  • 2021-11-30 16:07:21
The working principle of the injection molding machine is similar to the syringe used for injection. It uses the thrust of the screw (or plunger) to inject the plasticized plastic in the molten state (that is, the viscous fluid state) into the closed mold cavity. The process of obtaining the product after curing and shaping.

Injection molding is a cyclic process, each cycle mainly includes: quantitative feeding-melt plasticization-pressure injection-mold filling and cooling-mold opening and taking parts. After taking out the plastic part, the mold is closed again for the next cycle.

Injection molding machine operation items: Injection molding machine operation items include three aspects: control keyboard operation, electrical control system operation and hydraulic system operation. Carry out the injection process action, feeding action, injection pressure, injection speed, ejection type selection, temperature monitoring of each section of the barrel, injection pressure and back pressure adjustment, etc.

The molding process of a general screw injection molding machine is: first add granular or powdered plastic into the barrel, and make the plastic into a molten state through the rotation of the screw and heating of the outer wall of the barrel, and then the machine closes the mold and moves the injection seat forward. Make the nozzle close to the gate of the mold, and then pass the pressure oil into the injection cylinder to push the screw forward, so as to inject the melt into the closed mold with a lower temperature at a high pressure and a faster speed, and pass a certain amount of time. Time and pressure hold (also known as holding pressure), cooling to make it solidify and shape, then the mold can be opened to take out the product (the purpose of holding pressure is to prevent the backflow of the melt in the mold cavity, replenish the material in the mold cavity, and ensure the product With certain density and dimensional tolerances). The basic requirements of injection molding are plasticization, injection and molding. Plasticization is a prerequisite for realizing and ensuring 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 cavity (the average pressure in the cavity is generally between 20 and 45 MPa), so there must be a large enough 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 completeness, color, gloss, etc.; the second is the accuracy between the size and relative position; the third is the physical properties, chemical properties, and Electrical performance, etc. These quality requirements are different depending on the use occasions of the products, and the required scales are also different. The defects of the product mainly lie in the design of the mold, the manufacturing accuracy and the degree of wear. But in fact, the technicians of plastic processing plants often suffer from the difficult situation of using technological means to compensate for the problems caused by mold defects without great results.

The adjustment of the process in the production process is a necessary way to improve the quality and output of products. Because the injection 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 a few more times. If the pressure, temperature, and time are all adjusted together, it is easy to cause confusion and misunderstanding. If there is a problem, you don't know the reason. The measures and means to adjust the process are various. For example, there are more than ten possible solutions to the problem of product dissatisfaction, and one or two main solutions to the crux of the problem must be selected to truly solve the problem. In addition, attention should be paid to the dialectical relationship in the solution. For example: when the product has a depression, sometimes the material temperature must be increased, sometimes the material temperature must be lowered; sometimes the material quantity must be increased, and sometimes the material quantity must be reduced. It is necessary to recognize the feasibility of reversing measures to solve the problem.

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