Working Principle and Operation of Plastic Injection Molding Machine

August 01,2022

The working principle of the plastic injection molding machine is similar to that of a syringe 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 products after curing and shaping. Injection molding is a cyclic process, each cycle mainly includes: quantitative feeding - melting and plasticizing - 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.


The working principle and operation of plastic injection molding machine:


Plastic Injection Molding Machine


1) Locking the mold: The mold puller quickly approaches the fixed mold puller (including slow-fast-slow speed), and after confirming that there is no foreign matter, the system turns to high pressure to lock the mold (maintain the pressure in the cylinder).


2) The injection table moves forward: the injection table advances to the designated position (the nozzle is close to the mold).


3) Plastic injection molding: The screw can be set to inject the molten material at the front end of the barrel into the mold cavity at multiple speeds, pressures and strokes.


4) Cooling and pressure holding: According to the setting of various pressures and time periods, the pressure of the barrel is maintained, and the cavity is cooled and formed at the same time.


5) Cooling and pre-molding: the products in the mold cavity continue to cool, while the hydraulic motor drives the screw to rotate to push the plastic particles forward, and the screw retreats under the control of the set back pressure. When the screw retreats to the predetermined position, the screw stops rotating and the injection, the oil cylinder is released according to the setting, and it is expected to end.


6) The shooting table retreats: After the pre-molding, the shooting table retreats to the designated position.


7) Open the mold: the mold pulls back to the original position (including slow-fast-slow)


8) Ejection: The ejector pin ejects the product.


The basic requirements of injection molding are plasticizing, injection and molding. Plasticization is the premise to realize and ensure 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 mold cavity (the average pressure in the mold cavity is generally between 20 and 45MPa), 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 molding machine.