injection molding machine working principle

Injection molding machine

Injection molding machine is also known as injection molding machine or injection molding machine. It is the main molding equipment for making various shapes of plastic products from thermoplastic or thermosetting plastics using plastic molding molds. It is divided into vertical type, horizontal type and all-electric type. The injection molding machine heats the plastic and applies high pressure to the molten plastic to make it shoot out and fill the mold cavity.

working principle

• The working principle of the injection molding machine is similar to that of the syringe used for injection. It is the process of injecting the plasticized plastic in the molten state (i.e., viscous flow state) into the closed mold cavity with the help of the thrust of the screw (or plunger), and then obtaining the product after curing.

• Injection molding is a cycle process, each cycle mainly includes: quantitative feeding - melting and plasticizing - pressure injection - mold filling and cooling - mold opening and parts taking. Take out the plastic part and 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, 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 as follows: first, add granular or powdered 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 will close the mold and move the injection seat forward to make the nozzle close to the sprue of the mold, and then inject pressure oil into the injection cylinder to push the screw forward, Thus, the molten material can be injected into a closed mold with a low temperature at a high pressure and a fast speed. After a certain time and pressure (also known as pressure maintaining) and cooling, the mold can be solidified and shaped, and then the product can be taken out (the purpose of pressure maintaining is to prevent the reverse flow of molten material in the mold cavity, add 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, 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 (the average pressure in the mold cavity is generally between 20 and 45 MPa), so there must be enough 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 according to the use occasions of products. The defects of the products mainly lie in the design, manufacturing accuracy and wear degree of the molds. 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 with little effect.

• Process adjustment in the production process is a necessary way to improve product quality and output. Because the injection cycle itself is very short, if the process conditions are not well mastered, the waste products will be endless. When adjusting the process, it is better to change only one condition at a time and observe several times. If the pressure, temperature and time are all adjusted together, it is easy to cause confusion and misunderstanding. If there is a problem, we do not know why. There are many measures and means to adjust the process. For example, there are more than ten possible solutions to solve the problem of product dissatisfaction. Only by selecting one or two main solutions to solve 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 has a depression, sometimes the material temperature should be raised, sometimes the material temperature should be lowered; 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 problems.