Plastic moldInjection moldingThe whole process of molding includes feeding, plasticizing, mold filling, pressure maintaining, backflow, cooling and demoulding.

(1) Feeding

In the process of plastic mold injection molding, granular or powdered plastic needs to be added to the hopper of the injection machine, and then brought into the barrel by the plunger or screw for heating.

(2) Plasticization

The process of granular or powdery plastic heating and melting in the barrel in a flowing state is called plasticization.

(3) Mold filling

The molten plastic melt is pushed by the plunger or screw of the injection machine, enters the cavity of the plastic mold through the nozzle and gating system of the mold at a certain pressure and speed, and fills the cavity after a certain time. This stage is the mold filling stage in the plastic mold injection molding process.

(4) Pressure maintaining

After filling, under the push of the plunger or screw of the injection machine, the melt still maintains a certain pressure, so that the molten plastic in the barrel continues to enter the cavity, which is used to supplement the shrinkage of the plastic in the cavity of the plastic mold, so as to increase the density of the plastic parts and reduce the shrinkage of the products and the surface defects of the products. This stage is the stage of maintaining pressure in plastic mold injection molding.

(5) Backflow

After the pressure maintaining is completed, the plunger or screw of the injection molding machine will retract, which will release the pressure of molten plastic in the plastic mold cavity. At this time, the pressure of molten material in the cavity will be higher than that in front of the gate. If the gate has not condensed at this time, the molten material in the cavity will flow back to the pouring system of the mold through the gate, causing defects such as shrinkage, deformation and loose texture of the product. This phenomenon is called backflow. If the gate has condensed when the injection pressure is removed, there will be no backflow. Therefore, we can see whether backflow will occur and the degree of backflow is directly related to the holding time. Generally, if the pressure holding time is too long, the probability of backflow will be smaller.

(6) Cooling

The cooling process of plastic parts in the plastic mold refers to the whole process from the plastic melt at the gate to the plastic parts being pushed out of the mold cavity. At this time, stop feeding or backflow, and the plastic in the mold cavity continues to cool and set.

(7) Demoulding

When the product is cooled to a certain temperature and has sufficient strength to prevent warpage and deformation, the mold can be opened, and then the plastic part can be pushed out of the mold under the action of the ejector mechanism. This stage is the demoulding stage in plastic mold injection molding.