Introduction of injection molding principle and injection molding process: Injection molding (or injection molding) is a method of heating and melting plastic in the heating cylinder of injection molding machine, and then pushing the melt into the cavity of closed mold through plunger or reciprocating screw. It can not only produce high-precision and high-quality products with high productivity, but also process a variety of plastics, so injection molding is one of the important molding methods in plastic processing. A basic function of injection molding machine: injection molding is realized by injection molding machine. The basic function of injection molding machine is: 1. Heating the plastic to reach a molten state; 2。 High pressure is applied to the melt to make it eject and fill the mold cavity. B. Injection molding process/equipment: The injection molding operation of thermoplastics is generally through plasticization. Mold filling. Compaction and cooling, etc. The equipment used is an injection molding machine. Injection mold and auxiliary equipment (such as material drying, etc. C injection device: the injection device mainly realizes plasticization in the process of injection molding machine. Measure. Injection, pressure maintaining and feeding. Screw injection device is the most widely used, which combines screw plasticization and injection plunger into a single screw. Essentially, it should be called coaxial reciprocating compound rod injection device. When working, the plastic in the hopper falls into the heating barrel by its own weight, and the plastic moves forward along the spiral groove through the rotation of the screw. At this time, the material is heated by the heater outside the heating barrel, and at the same time, there is heat generated by shearing inside, and the temperature rises to the molten state. With the storage of materials in the front end of the heating cylinder, the reaction force (back pressure) generated by these materials pushes the screw backward, and the limit switch is used to limit its retreat. When it retreats to a certain position, the screw stops rotating, thus determining (metering) the injection amount at one time. After the material in the mold is cooled, once the product is taken out, the mold is closed again and the injection process is entered. At this time, the hydraulic cylinder (injection cylinder) of the injection device exerts force on the screw, which becomes a shooting rod under high pressure, and the melt at the front end of the screw is injected into the mold from the nozzle. Screw injection device consists of screw, barrel, nozzle and driving device. Screw for injection is generally divided into three stages: feeding, compression and metering. The compression ratio is 2~3, and the length-diameter ratio is 16~ 18. When the melt is ejected from the nozzle, a part of the melt will flow back through the spiral groove because the injection force on the pressurized melt is afraid of the reaction force. In order to prevent this phenomenon, a check valve is installed at the end of the screw. For rigid PVC, use tapered screw heads. The barrel is the part where the screw is fixed and is made of heat-resistant material. Made of high-pressure resistant steel. The electric coil array is installed at the periphery of the barrel to heat the material in the barrel, and the temperature is controlled by a thermocouple to make the plastic have a suitable temperature. The nozzle is a transitional part connecting the barrel and the mold, and it is equipped with an independent heating ring, because it is an important part that directly affects the melting state of plastic. Generally, open nozzles are often used in the injection molding of low viscosity poly (monoamide). Needle valve type nozzle is adopted. The rotation of the driving screw can be a motor or a hydraulic motor, and the reciprocating motion of the screw is realized by hydraulic pressure. The parameters of the injection molding machine characterized by the injection device are as follows: the injection quantity refers to the maximum quantity injected into the mold by the injection molding machine each time, which can be expressed by the injected polystyrene melt quality or the injected melt volume; Injection pressure refers to the pressure exerted on the cross section of the barrel during injection; Injection speed refers to the moving speed of the screw during injection. D mold clamping device: besides opening and closing the mold, the main task of the mold clamping device is to resist the high pressure of the melt injected into the mold with enough force, thus locking the mold. Don't let it open Whether the clamping mechanism is mechanical, hydraulic or hydro-mechanical, the mold should be opened and closed flexibly, punctually, quickly and safely. From the technical requirements, the opening and closing of the mold must have a buffering effect. When closing the mold, the running speed of the template should be fast first and then slow, and when opening the mold, it should be slow first and then slow. So as to prevent damage to molds and products. In the molding process, the force exerted on the mold to keep the mold closed is called clamping force, and its value should be greater than the product of the cavity pressure and the projected area of the part (including shunt). The average pressure in the mold cavity is usually between 20 and 45 MPa. Because the clamping force reflects the size of the molded product area of the injection molding machine in detail, the maximum clamping force of the injection molding machine is often used to represent the specifications of the injection molding machine, but there is also a roughly proportional relationship between the clamping force and the injection quantity. However, the expression of clamping force can not directly reflect the size of injection molded products, so it is inconvenient to use. Many international manufacturers use locking force/equivalent injection quantity to express the specifications of injection molding machines. For injection quantity, in order to have the same comparison standard for different machines, the theoretical injection quantity is specified when the injection pressure is 100Mpa, that is, equivalent injection quantity = theoretical injection quantity * rated injection pressure/100Mpa. E control system: the hydraulic control system of injection molding machine is mainly divided into conventional hydraulic control system, servo control system and proportional control system. Due to the complexity of the hydraulic system, the proportional valve oil system is taken as an example to illustrate the outline here. The characteristic of this system is that there are proportional components (electromagnetic proportional flow valve or electromagnetic proportional flow reversing valve, electromagnetic proportional pressure valve) in the oil circuit system to control flow and pressure. Through the proportional action of external electric analog signal and magnetic force, the opening of the valve core or the spring force of the valve core can be controlled to control the flow or pressure of the system, so as to realize the injection speed, screw speed, opening and closing speed and injection pressure. Keep the pressure. Screw torque. Injection seat thrust. The protection pressure of jacking die is controlled by single stage, multi-stage or stepless.