March 24, 2023
Working principle of injection molding machine
The working principle of an injection molding machine is similar to that of an injector used for injection. It is a process that uses the thrust of a screw (or plunger) to inject plasticized plastic in a molten state (i.e., a viscous flow state) into a closed mold cavity, and then solidify and shape it to obtain a product.
Injection molding is a cyclic process, each cycle mainly includes: quantitative feeding - melting and plasticizing - pressure injection - mold filling and cooling - mold opening and parts taking. After taking out the plastic part, close the mold again and proceed to the next cycle.
Injection molding machine operation project: The injection molding machine operation project includes three aspects: control keyboard operation, electrical control system operation, and hydraulic system operation. Select the injection process action, feeding action, injection pressure, injection speed, ejection type, monitor the temperature of each section of the barrel, and adjust the injection pressure and back pressure.
The molding process of a general screw injection molding machine is as follows: first, add granular or powdered plastic into the barrel, and through the rotation of the screw and the heating of the outer wall of the barrel, the plastic becomes molten. Then, the machine performs mold closing and the injection seat moves forward, making the nozzle close to the gate of the mold, and then inject pressure oil into the injection cylinder to advance the screw, Thus, the molten material is injected into a closed mold with a low temperature at a high pressure and a fast speed. After a certain period of time and pressure maintenance (also known as pressure maintaining), cooling, and solidification, the mold can be opened and the product can be taken out (the purpose of pressure maintaining is to prevent the reverse flow of molten material in the mold cavity, replenish material into the mold cavity, and ensure that the product has a certain density and dimensional tolerance). The basic requirements for injection molding are plasticization, injection, and molding. Plasticization is a prerequisite for achieving and ensuring the quality of molded products, and in order to meet the molding requirements, injection must ensure sufficient pressure and speed. At the same time, due to the high injection pressure, a relatively high pressure is generated in the mold cavity (the average pressure in the mold cavity is generally between 20 and 45 MPa), so there must be sufficient clamping force. It can be seen that the injection device and the 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, gloss, etc; The second is the accuracy between size and relative position; The third is the physical, chemical, and electrical properties corresponding to the purpose. These quality requirements vary depending on the use situation of the product and the required scale. The defects of products mainly lie in mold design, manufacturing accuracy, and wear degree. However, in fact, technical personnel in plastic processing plants often face the difficult situation of using technological means to compensate for the problems caused by mold defects with little success.
Process regulation during production is a necessary way to improve product quality and output. Due to the short injection molding cycle itself, 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 only change one condition at a time and observe it several times. If the pressure, temperature, and time are all adjusted together, it can easily cause confusion and misunderstanding, and if there is a problem, it is not clear why. The measures and means for adjusting the process are various. For example, there are more than ten possible solutions to the problem of product dissatisfaction, and it is necessary to choose one or two main solutions to solve the problem in order to truly solve the problem. In addition, attention should also be paid to the dialectical relationship in the solution. For example, if the product has a depression, sometimes it is necessary to increase the material temperature, and sometimes it is necessary to reduce the material temperature; Sometimes it is necessary to increase the material quantity, and sometimes it is necessary to reduce the material quantity. The feasibility of solving problems through reverse measures should be recognized.