What is the working principle of injection molding machine

The working principle of the injection molding machine is similar to that of the syringe used for injection. It uses the thrust of the screw (or plunger) to inject the plasticized molten state (i.e. viscous flow state) plastic into the closed mold cavity, and obtains the product after solidification and shaping.
Injection molding is a cyclic process. Each cycle mainly includes: quantitative feeding - melting and plasticization - pressure injection - mold filling and cooling - mold opening and taking out the parts. After taking out the plastic parts, 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. The injection process action, feeding action, injection pressure, injection speed, ejection type selection, monitoring of the temperature of each section of the barrel, and adjustment of injection pressure and back pressure are performed respectively.
The molding process of a general screw injection molding machine is: first, add granular or powdered plastic into the barrel, and make the plastic molten by rotating the screw and heating the outer wall of the barrel. Then the machine closes the mold and moves the injection seat forward, so that the nozzle is close to the gate of the mold. Then, the pressure oil is introduced into the injection cylinder to push the screw forward, so that the molten material is injected into the closed mold with a lower temperature at a very high pressure and a faster speed. After a certain period of time and pressure maintenance (also known as pressure holding), cooling, it is solidified and formed, and then the mold can be opened to take out the product (the purpose of pressure holding is to prevent the backflow of the molten material in the mold cavity, to add materials to the mold cavity, and to 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 for achieving 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 high pressure is generated in the mold cavity accordingly (the average pressure in the mold cavity is generally between 20 and 45 MPa), so there must be a sufficiently large 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 between size and relative position; the third is the physical properties, chemical properties, electrical properties, etc. corresponding to the purpose. These quality requirements are different according to the different occasions of product use. The defects of the product are mainly in the design, manufacturing accuracy and wear degree of the mold. But in fact, the technicians of the plastic processing plant often suffer from the difficult situation of using process means to make up for the problems caused by mold defects without much effect.
The adjustment of the process in the production process is a necessary way to improve the quality and output of products. Since the injection molding cycle itself is very short, if the process conditions are not well controlled, there will be an endless supply 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 adjusted together, it is easy to cause confusion and misunderstanding, and it is unknown why there is a problem. There are many measures and means to adjust the process. For example, there are more than ten possible solutions to the problem of product filling failure. Only by selecting one or two main solutions to solve the problem can the problem be truly solved. In addition, attention should be paid to the dialectical relationship in the solution. For example, when a product is dented, sometimes the material temperature should be increased, sometimes it should be lowered; sometimes the material quantity should be increased, sometimes it should be reduced. The feasibility of solving the problem by reverse measures should be recognized.