Guide to the working principle of injection molding machine

SS Machinery

The working principle of the injection molding machine is similar to the syringe 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 fluid state) into the closed mold cavity. The process of obtaining products after curing and shaping.

Injection molding is a cyclic process, each cycle mainly includes: quantitative feeding-melting and plasticizing-pressure injection-filling and cooling-mould opening and taking parts. After taking out the plastic part, the mould is closed again for the next cycle.


Structure of the Injection Molding Machine

According to the plasticizing method, the injection molding machine is divided into plunger injection moulding machine and screw injection molding machine. 

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 is divided into automatic, Semi-automatic, manual injection moulding machine.


Type of Injection Molding Machine

(1) Horizontal injection molding machine: This is the most common type. The clamping part and the injection part are on the same horizontal centerline, and the mould is opened in the horizontal direction. Its characteristics are: the body is short, easy to operate and maintain; the machine has a low centre of gravity, and the installation is relatively stable; after the product is ejected, it can automatically fall by gravity, and it is easy to realize fully automatic operation. At present, most of the injection molding machines on the market adopt this type.


(2) Vertical injection molding machine: its clamping part and injection part are on the same vertical centerline, and the mold is opened in the vertical direction. Therefore, it occupies a small area, it is easy to place inserts, it is convenient to load and unload the mold, and the material falling from the hopper can be plasticized more evenly. However, the product is not easy to automatically fall after being ejected, and must be removed by hand, which is not easy to realize automatic operation. Vertical injection molding machines are suitable for small injection molding machines. Generally, injection molding machines below 60 grams are more commonly used. Large and medium-sized machines are not suitable.


(3) Angle injection molding machine: its injection direction and the mold interface are on the same surface. It 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 are prone to tilt and fall. This type of injection molding machine is suitable for small machines.


(4) Multi-mode turntable injection molding machine: It is a special injection molding machine with the multi-station operation. Its characteristic is that the mold clamping device adopts a turntable structure and the mold rotates around the shaft. This type of injection molding machine gives full play to the plasticizing ability of the injection device, can shorten the production cycle, and increase the production capacity of the machine. Therefore, it is particularly suitable for large quantities of products that require a long cooling and setting time or require more auxiliary time due to the placement of inserts. Production. However, due to the large and complex mold clamping system, the clamping force of the mold clamping device is often small, so this type of injection molding machine is often used in the production of plastic shoe soles and other products.


The basic requirements of injection molding are plasticization, injection and molding. Plasticization is a prerequisite for realizing and ensuring 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, correspondingly high pressure is generated in the cavity (the average pressure in the cavity is generally between 20 and 45 MPa), so there must be a sufficient clamping force. It can be seen that the injection device and the clamping device are the key components of the injection moulding machine.


Action Program of Injection Molding Machine

Clamping → Pre-molding → Reverse → Nozzle advance → Injection → Hold pressure → Nozzle retreat → Cooling → Open mold → eject → Open door → Take workpiece → Close door → Close mold.

Injection molding machine operation items: Injection molding machine operation items 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, temperature, current, and voltage monitoring of each section of the barrel, adjustment of injection pressure and back pressure, etc. are performed respectively.


After the injection is over and the cooling timer finishes, the pre-plastic action starts. The screw rotates to squeeze the molten plastic material to the front of the screw head. Due to the action 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 back. When the screw retreats to a predetermined position (this position is determined by the travel switch, which controls the retreat distance of the screw to achieve quantitative feeding), the pre-plasticizing stops and the screw stops rotating. This is followed by a retraction action, which means that the screw makes a slight axial retreat. This action can relieve the pressure of the melt gathered at the nozzle and overcome the "salivation" phenomenon caused by the imbalance of pressure inside and outside the barrel. If there is no need to retract, the retract should be stopped and the switch should be adjusted to the appropriate position to stop the pre-moulding. The same moment the switch is pressed, the retract stop switch is also pressed. When the screw retreats to press the stop switch, the retraction stops. Then the betting began to retreat. When the injection seat retreats until the stop switch is pressed, the injection seat stops retreating. If a fixed feeding method is used, attention should be paid to adjusting the position of the travel switch.


Generally, a fixed feeding method is used in general production to save the time of the injection seat advance and retreat and speed up the production cycle.


About Us

ss Machinery is a professional manufacturer of injection molding machines. It is also the leading brand of small injection molding machines in China. Customize and produce various types of molding machines for customers.

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