In the process of injection molding of plastic varieties, due to the volume change caused by crystallization, the pressure during injection molding is high, the viscosity difference of molten material is small, the shear stress between layers is small, and the elastic rebound after demoulding is large. Therefore, the shrinkage during injection molding can also be reduced appropriately. The material temperature is high and the shrinkage is large, but its directivity is small.

When the pressure increases during the pressure injection molding process, the molten material will be subject to greater shearing, and the fluidity will also increase. Especially PE and POM are more sensitive, so the pressure during the injection molding process should be adjusted to control the fluidity. During molding, the material temperature, mold temperature, pressure during injection processing, injection speed and other factors can also be controlled to properly adjust the filling to meet the molding needs.