Injection molding machine maintenance methods and experience summary

       1.1 The working principle of injection molding machine

       The working principle of the injection molding machine is similar to that of the injector used for injection. It uses the thrust of the screw (or plunger) to inject the plasticized plastic in the molten state (that is, the viscous state) into the closed mold cavity. The process of obtaining a product after curing and shaping.

       Injection molding is a cyclic process, each cycle mainly includes: quantitative feeding - melt plasticization - pressure injection - mold filling and cooling - mold opening and taking out. After the plastic parts are taken out, the mold is closed again for the next cycle.

       1.2 The structure of the injection molding machine

       According to the plasticizing method, the injection molding machine is divided into plunger injection molding machine and screw injection molding machine; according to the transmission method of the machine, it can be divided into hydraulic type, mechanical type and hydraulic-mechanical (connecting rod) type; according to the operation method, it can be divided into active, Semi-active, manual injection molding machine.

       (1) Horizontal injection molding machine: This is the more common type. The mold clamping part and the injection part are on the same horizontal centerline, and the mold is opened in the horizontal direction. Its characteristics are: the body is short, easy to operate and repair; the center of gravity of the machine is low, and the equipment is relatively stable; after the product is ejected, it can be automatically dropped by gravity effect, which is easy to complete automatic operation. At present, most of the injection molding machines on the market use this type.

       (2) Vertical injection molding machine: The clamping part and the injection part are on the same straight center line, and the mold is opened in a straight direction. Therefore, the floor area is small, the inserts are simply placed, the loading and unloading of the mold is more convenient, and the material falling from the hopper can be plasticized more uniformly. However, after the product is ejected, it is not easy to automatically fall, and it must be removed by hand, which is not easy to complete the automatic operation. Vertical injection molding machines are suitable for small injection molding machines. Generally, injection molding machines below 60 grams are used more, and large and medium-sized machines should not be used.

       (3) Angle injection molding machine: The injection direction and the mold interface are on the same plane, which is especially suitable for flat products that do not allow gate marks in the machining center. It occupies a smaller area than a horizontal injection molding machine, but the inserts placed in the mold tend to fall off easily. This type of injection molding machine is suitable for small machines.

       (4) Multi-mode rotary table injection molding machine: It is a special injection molding machine with multi-station operation. This type of injection molding machine gives full play to the plasticizing ability of the injection equipment, which can shorten the production cycle and improve the production ability of the machine. Therefore, it is especially suitable for large-scale plastics with long cooling and setting time or requiring more auxiliary time due to the placement of inserts. However, due to the huge and complicated clamping system, the clamping force of the clamping equipment is often small, so this injection molding machine is used more in the production of products such as plastic shoe soles.

       The general injection molding machine includes injection equipment, mold clamping equipment, hydraulic system and electrical control system.

       The basic requirements of injection molding are plasticization, injection and molding. Plasticization is a condition to complete and ensure the quality of molded products, and in order to meet the requirements of molding, injection must ensure satisfactory pressure and speed. At the same time, because the injection pressure is very high, a correspondingly high pressure occurs in the cavity (the average pressure in the cavity is generally between 20 and 45MPa, so it is necessary to have a large clamping force. It can be seen that the injection Equipment and clamping equipment are the key components of injection molding machines.

       1.4 Operation of injection molding machine

       1.4.1 Action program of injection molding machine

       Nozzle travel → injection → pressure maintenance → pre-molding → retraction → nozzle withdrawal → cooling → mold opening → ejection → needle withdrawal → door opening → door closing → mold closing → nozzle travel.

       1.4.2 Injection molding machine operation items: The injection molding machine operation items include three aspects: keyboard operation, electrical control cabinet operation and hydraulic system operation. The selection of injection process action, feeding action, injection pressure, injection speed, ejection type, monitoring of temperature, current and voltage of each section of the barrel, adjustment of injection pressure and back pressure pressure, etc. are carried out separately.

       1.4.2.1 Action selection of injection process:

       Generally, injection molding machines can be operated manually, as well as semi-active and fully-active.

       Manual operation is in a production cycle, and each action is completed by the operator flipping the operation switch. Generally, it is only selected when testing the machine and adjusting the mold.

       In semi-active operation, the machine can automatically complete the action of a working cycle, but after each production cycle, the operator must swing the safety door, remove the workpiece, and then close the safety door, so that the machine can continue the production of the next cycle.

       In fully automatic operation, the injection molding machine can automatically enter the next operation cycle after completing the action of one operation cycle. During normal continuous operation, no downtime is required for control and adjustment. However, it should be noted that if full-automatic operation is required, (1) do not open the safety door halfway, otherwise the full-automatic operation will be terminated; (2) feed materials in time; (3) if electric eye induction is used, be careful not to cover the electric eye.

       In fact, it is generally necessary to temporarily stop halfway in the fully automatic operation, such as spraying mold release agent to the machine mold.

       During normal production, semi-active or fully active operation is generally used. At the beginning of the operation, the operation method (manual, semi-automatic or fully automatic) should be selected according to the production requirements, and the manual, semi-automatic or fully automatic switch should be toggled accordingly.

       The semi-active and fully-active operating procedures have been determined by the circuit itself. The operator only needs to change the speed and pressure on the electric cabinet, the length of time, the number of thimbles, etc., and the operator will not adjust the wrong button. And make the operation program appear disordered.

       When each action in a cycle is not adjusted properly, manual operation should be selected first, and after each action is confirmed to be normal, semi-active or fully active operation should be selected.

       1.4.2.2 Selection of pre-molding action

      According to whether the injection seat retreats before and after the pre-plastic feeding, that is, whether the nozzle is separated from the mold, the injection molding machine generally has three options. (1) Fixed feeding: the nozzle is always attached to the mold before and after pre-molding, and the injection seat does not move. (2) Pre-feeding: The nozzle is pressed against the mold for pre-plastic feeding. After pre-plasticizing, the injection seat is withdrawn and the nozzle is separated from the mold. The purpose of choosing this method is to use the mold pinhole to assist the nozzle during pre-molding to prevent the melt from flowing out of the nozzle when the back pressure is high. Their respective temperatures are relatively stable. (3) Post-feeding: After the injection is completed, the injection seat retreats, the nozzle is separated from the mold and then pre-molded, and the injection seat moves forward after pre-molding. This action is suitable for processing plastics with a particularly narrow molding temperature, because the contact time between the nozzle and the mold is short, preventing heat loss