This molding process was developed for molding optical lens surfaces. The molding process is as follows: the mold is first clamped, but the movable mold and the fixed mold are not completely closed, and a certain compression gap is reserved, and then the melt is injected into the cavity; after the melt injection is completed, the special closed-die piston is implemented. In the cross mold, the melt in the cavity flows and compacts again during the complete closing of the mold.
Compared with general injection molding, injection-compression molding is characterized by:
(1) The melt injection is carried out in the case where the cavity is not completely closed, so that the flow passage area is large, the flow resistance is small, and the required injection pressure is also small.
(2) The melt shrinkage is compensated by externally applying pressure to the cavity to make the cavity size small (the cavity directly compresses the melt), and thus the cavity is uniformly distributed in pressure.
Therefore, injection-compression molding can reduce or eliminate the molecular orientation and internal stress caused by filling and packing, improve the uniformity of the material of the product and the dimensional stability of the product, and at the same time reduce the residual stress of the plastic part. Injection-compression molding processes have been widely used to shape plastic optical lenses. High-precision plastic parts such as laser discs and thin-walled plastic parts that are difficult to inject. In addition, the application of injection-compression molding in the formation of glass fiber reinforced resin is also becoming increasingly popular.