3 Keys Stages of Injection Moulding

The plastic injection moulding process is a cycle process. Once the once cycle is completed, the once injection moulding cycle is completed. Each cycle mainly includes quantitative feeding, melt plasticizing, pressure injection, mould filling, cooling, and mould opening and removal of injection moulded parts. After removing the plastic part, the mould is closed and the next cycle is performed. Each time the injection moulding cycle is completed, the injection device and the clamping device of the injection moulding machine respectively complete once working cycle, that is, the moving parts of the injection device and the clamping device are sequentially operated once in a predetermined order. There are 3 keys stages to complete injection moulding: plasticization, injection, and moulding.

Plasticization stage
The plastic material falls from the hopper into the barrel and is conveyed forward by the rotating screw. In the barrel, the plastic receives the heating from the outside of the barrel on the one hand, and is compacted by the gradual decrease of the volume of the groove on the other hand, and stirs and shears the plastic when the screw rotates in the barrel. The cutting action causes intense friction between the plastics and the barrel and the screw, generating a large amount of heat, causing the plastic to gradually plasticize into a molten state while being pushed forward. Due to the back pressure of the screw head, the screw rotates while still retreating to store the plasticized melt at the top of the barrel for injection. The screw retraction stroke is determined by the amount of shot material required for injection moulded parts.

Injection stage
When the screw stops rotating and retreats, the mould clamping part starts to work to close the mould, and then the injection device moves forward, so that the injection nozzle and the mould gate fit together, and the injection cylinder piston pushes the screw to move forward rapidly, the melt plastics are injected into mould cavity according to the required injection pressure and speed. In order to prevent the reflow of the molten material injected into the cavity and to replenish the small amount of melt required for shrinking due to the cooling of the product, the screw after the injection is still required to maintain a certain pressure on the melt, that is, the holding pressure.

Moulding stage
After the melt in the cavity cools, it returns to the glass state from the viscous flow state. After the product in the cavity is completely cooled and shaped, the clamping mechanism is opened, the mould is opened, and under the auxiliary action of the ejection mechanism, the product is demoulded, and the whole process of injection moulding is completed.