Lianbang injection molding machine is used for injection molding products. The products are very wide, such as notebook, LCD frame, mobile phone case, TV case, etc. almost all plastic parts are made in this way. The following is the working principle of the injection molding machine and the injection molding process:

1. The working principle of injection molding machine the working principle of injection molding machine is similar to that of injection syringe. It is a technological process of injecting the plastic in the molten state (i.e. viscous flow state) which has been plasticized into the closed mold cavity with the help of the thrust of screw (or plunger), and obtaining the products after curing and finalizing. Injection molding is a cycle process, each cycle mainly includes: quantitative feeding - melting and plasticizing - pressure injection - mold filling and cooling - mold opening and taking. Take out the plastic part and then close the mold for the next cycle.

2. The structural injection molding machine of injection molding machine can be divided into plunger type injection molding machine and screw type injection molding machine according to the plasticizing mode. According to the transmission mode of the machine, it can be divided into hydraulic type, mechanical type and hydraulic mechanical (connecting rod) type. According to the operation mode, it can be divided into automatic, semi-automatic and manual injection molding machines.

(1) Horizontal injection molding machine: This is the most common type. The mold closing part and the injection part are on the same horizontal center line, and the mold is opened in the horizontal direction. Its features are: short fuselage, easy to operate and maintain; low center of gravity of the machine, relatively stable installation; after the product is ejected, it can automatically fall down by gravity, easy to realize full-automatic operation. At present, this type of injection molding machine is widely used in the market.

(2) Vertical injection molding machine: the mold closing part and the injection part are on the same vertical center line, and the mold is opened in the vertical direction. Therefore, the utility model has the advantages of small floor area, easy placement of inserts, convenient loading and unloading of molds, and even plasticization of materials falling into the hopper. However, it is not easy for the product to fall down automatically after ejection. It must be taken down by hand, and it is not easy to realize automatic operation. Vertical injection molding machine is suitable for small-scale injection molding machine, generally less than 60g injection molding machine is used more, large and medium-sized machines are not suitable. 

(3) Angle type injection molding machine: its injection direction is on the same surface as the mold interface, which is especially suitable for plane products with no gate trace in the machining center. It covers a smaller area than horizontal injection molding machine, but the inserts put into the mold are easy to fall obliquely. This type of injection molding machine is suitable for small machines.

(4) Multi mode rotary injection molding machine: it is a special injection molding machine with multi position operation. Its feature is that the mold closing device adopts the rotary structure, and the mold rotates around the rotating shaft. This type of injection molding machine can make full use of the plasticizing ability of the injection device, shorten the production cycle and improve the production capacity of the machine, so it is especially suitable for the production of large quantities of products with long cooling setting time or more auxiliary time due to the placement of inserts. However, due to the large and complex clamping system, the clamping force of the clamping device is often small, so this injection molding machine is widely used in the production of plastic sole and other products.

General injection molding machine includes injection device, mold closing device, hydraulic system and electrical control system. The basic requirements of injection molding are plasticization, injection and molding. Plasticization is the premise of realizing and ensuring the quality of molded products, and in order to meet the requirements of molding, injection must be guaranteed to have enough pressure and speed. At the same time, due to the high injection pressure, the corresponding high pressure is generated in the cavity (the average pressure in the cavity is generally between 20 and 45MPa), so there must be enough mold closing force. It can be seen that the injection device and the mold closing device are the key parts of the injection molding machine.

3. Operation of injection molding machine

3.1 action program of injection molding machine: mold closing → pre molding → backward shrinking → nozzle forward → injection → pressure maintaining → nozzle backward → cooling → mold opening → ejection → door opening → workpiece taking → door closing → mold closing. 

3.2 operation items of injection molding machine: the operation items of injection molding machine include control keyboard operation, electrical control cabinet operation and hydraulic system operation. The selection of injection process action, feeding action, injection pressure, injection speed, ejection form, monitoring of temperature, current and voltage of each section of the barrel, adjustment of injection pressure and back pressure, etc.

3.2.1 the general injection molding machine can be operated manually, semi-automatic and full-automatic. Manual operation is in a production cycle, and each action is realized by the operator moving the operation switch. Generally, it is selected when the machine is tested and adjusted. During semi-automatic operation, the machine can automatically complete a work cycle, but after each production cycle, the operator must open the safety door, remove the workpiece, and then close the safety door, the machine can continue the next cycle of production. When fully automatic operation, the injection molding machine can automatically enter the next working cycle after completing the action of one working cycle. In the normal continuous working process, there is no need to stop for control and adjustment. However, it should be noted that if full-automatic operation is required, (1) do not open the safety door in the middle of the process, or the full-automatic operation will be interrupted; (2) feed materials in time; (3) if electric eye induction is selected, attention should be paid not to cover the electric eye. In fact, it is usually necessary to stop the machine temporarily in the process of full-automatic operation, such as spraying mold release agent on the machine mould. In normal production, semi-automatic or full-automatic operation is generally selected. At the beginning of operation, the operation mode (manual, semi-automatic or full-automatic) shall be selected according to the production needs, and the manual, semi-automatic or full-automatic switch shall be set accordingly. The semi-automatic and full-automatic working procedures have been determined by the line itself. The operator only needs to change the speed and pressure, the length of time, the number of thimbles, etc. on the electric cabinet surface, so as not to cause confusion in the working procedures due to the operator's wrong key adjustment. When each action in a cycle is not adjusted properly, manual operation shall be selected first. After confirming that each action is normal, semi-automatic or full-automatic operation shall be selected.

3.2.2 the selection of pre molding action is based on whether the injection seat back before and after the pre molding feeding, i.e. whether the nozzle leaves the mold. Generally, there are three choices for the injection molding machine. (1) Fixed feeding: before and after pre molding, the nozzle is always attached to the mold, and the injection seat does not move.

(2) Front feeding: the nozzle carries out pre plastic feeding against the mold. After pre plastic, the injection seat moves backward and the nozzle leaves the mold. The purpose of selecting this method is to use the injection hole of the mold to hold the nozzle during the pre molding to prevent the molten material from flowing out of the nozzle when the back pressure is high. After the pre molding, the heat transfer caused by the long-term contact between the nozzle and the mold can be avoided, which will affect the relative stability of their respective temperatures.

(3) After feeding: after injection, the injection seat moves backward, the nozzle leaves the mold and then the injection seat moves forward after the injection. The action is suitable for processing plastic with a narrow molding temperature. Due to the short contact time between the nozzle and the mold, the heat loss is avoided, and the solidification of the melt in the nozzle hole is also avoided. After the injection and cooling timer are finished, the pre molding starts. The screw rotates to squeeze the plastic melt to the front of the screw head. Due to the function of the one-way valve at the front end of the screw, the molten plastic accumulates at the front end of the barrel, forcing the screw backward. When the screw retreats to the predetermined position (this position is determined by the travel switch, which controls the screw's retreating distance to realize quantitative feeding), the pre molding stops and the screw stops rotating. Then there is the backward shrinking action, that is, the screw makes a small amount of axial backward, which can release the pressure of the molten material gathered at the nozzle and overcome the "salivation" phenomenon caused by the imbalance of the internal and external pressure of the barrel. If it is not necessary to back shrink, stop the back shrink and turn the switch to the appropriate position to stop the pre molding. At the same time when the switch is pressed, the retraction stop switch is also pressed. When the screw moves backward to the press up stop switch, the backward retraction stops. Then the injection seat began to move backward. When the injection seat moves back to the press stop switch, the injection seat stops moving back. If fixed feeding mode is adopted, pay attention to adjust the position of travel switch. In general, fixed feeding mode is used to save the operation time of injection seat and speed up the production cycle.