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The working principle of an injection molding machine is similar to that of a syringe used for injection. It uses the thrust of a screw (or plunger) to inject the melted plastic (i.e. viscous flow state) that has already been plasticized into a closed mold cavity. After solidification and shaping, it is the process of obtaining the product.
Injection molding is a cyclic process, each cycle mainly includes: quantitative feeding - melting and plasticization - pressure injection - mold filling and cooling - mold opening and part taking. After removing 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, and ejection type separately, monitor the temperature of each section of the material barrel, and adjust the injection pressure and back pressure.
The molding process of a general screw injection molding machine is as follows: first, granular or powdered plastic is added to the barrel, and the plastic is melted by the rotation of the screw and 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 sprue of the mold. Then, pressure oil is introduced into the injection cylinder to push the screw forward, Thus, the molten material is injected into a closed mold with high pressure and fast speed at a lower temperature. After a certain period of time and pressure maintenance (also known as pressure holding) and cooling, it is solidified and formed, and the product can be opened and taken out (the purpose of pressure holding is to prevent the reverse flow of molten material in the mold cavity, supplement materials 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 to meet the requirements of molding, injection must ensure sufficient pressure and speed. At the same time, due to the high injection pressure, a corresponding high pressure is generated in the mold cavity (the average pressure inside the mold cavity is generally between 20 and 45 MPa), so there must be sufficient clamping force. It can be seen from this that the injection device and the clamping device are key components of the injection molding machine.
There are three main aspects to evaluate 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, chemical, and electrical properties corresponding to the intended use. These quality requirements vary according to the different usage scenarios of the products, and the required scales also vary. The defects of the product mainly lie in the design, manufacturing accuracy, and wear degree of the mold. However, in fact, technicians in plastic processing plants often face difficulties in using technological means to compensate for mold defects without achieving significant results.
Adjusting the process 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 controlled, waste products will continue to flow. When adjusting the process, only one condition is changed at a time, and multiple observations are made. If the pressure, temperature, and time are all adjusted together, it is easy to cause confusion and misunderstanding. If there is a problem, it is unclear why. The measures and means of adjusting the process are multifaceted. For example, there are more than ten possible ways to solve the problem of product dissatisfaction. To truly solve the problem, it is necessary to choose one or two main solutions to solve the crux of 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 needs to be raised, and sometimes the material temperature needs to be lowered; Sometimes it is necessary to increase the amount of material, and sometimes it is necessary to reduce the amount of material. To acknowledge the feasibility of reverse measures in solving problems.
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