Working principle of injection molding machine

The working principle of the injection molding machine is similar to that of the syringe for injection. It is the process of injecting the plasticized molten plastic (i.e. viscous flow) into the closed mold cavity with the help of the thrust of the screw (or plunger), and obtaining the product after curing and shaping.
Injection molding is a cycle process, each cycle mainly includes: quantitative feeding – melting and plasticization – pressure injection – mold filling and cooling – mold opening and taking parts. After taking out the plastic part, close the mold 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. Select the injection process action, feeding action, injection pressure, injection speed and ejection type, monitor the temperature of each section of the barrel, and adjust the injection pressure and back pressure.
The molding process of general screw injection molding machine is: first, add granular or powdery plastic into the barrel, and make the plastic melt through the rotation of the screw and the heating of the outer wall of the barrel, then the machine closes the mold and moves the injection seat forward to make the nozzle close to the gate of the mold, and then inject pressure oil into the injection cylinder to push the screw forward, Thus, the molten material is injected into the closed mold with low temperature at a high pressure and fast speed. After a certain time and pressure maintenance (also known as pressure holding) and cooling, the mold can be opened and the product can be taken out (the purpose of pressure holding is to prevent the reverse flow of molten material in the mold cavity, supplement materials to the mold cavity, and ensure that the product has a certain density and dimensional tolerance). The basic requirements of injection molding are plasticization, injection and molding. Plasticization is the premise to realize and ensure the quality of molded products. 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 high pressure is generated in the mold cavity (the average pressure in the mold cavity is generally between 20 ~ 45MPa), so there must be a large enough clamping force. It can be seen that the injection device and clamping device are the key components of the injection molding machine.
The evaluation of plastic products mainly includes three aspects: the first is the appearance quality, including integrity, color, luster and so on; The second is the accuracy between size and relative position; The third is the physical, chemical and electrical properties corresponding to the application. These quality requirements are different according to the different application occasions of products, and the required scales are also different. The defects of products mainly lie in mold design, manufacturing accuracy and wear degree. But in fact, the technicians of plastic processing plants often suffer from the difficult situation of using technological means to make up for the problems caused by mold defects.
The adjustment of process in the production process is a necessary way to improve the product quality and output. 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 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, I don’t know the reason. There are many measures and means to adjust the process. For example, there are more than ten possible solutions to the problem of dissatisfaction with product injection. Only by selecting one or two main solutions to solve the crux of the problem can we really solve the problem. In addition, attention should also be paid to the dialectical relationship in the solution. For example, if the product is sunken, sometimes the material temperature should be increased and sometimes the material temperature should be reduced; Sometimes it is necessary to increase the material quantity, and sometimes it is necessary to reduce the material quantity. We should recognize the feasibility of reverse measures to solve the problem.

Post time: Aug-27-2021