The program control of the injection speed is to divide the injection stroke of the screw into 3 to 4 stages, and each of the stages uses an appropriate injection speed. For example, when the molten plastic just starts to pass through the gate, the injection speed is slowed down, and during the filling process, high-speed injection is used, and the speed is slowed down at the end of filling. With such a method, it is possible to prevent flashing, eliminate flow marks, and reduce residual stress of the product.

The flow rate is stable at low speed filling, the product size is relatively stable, the fluctuation is small, the internal stress of the product is low, and the internal and external stresses of the product tend to be uniform (for example, a polycarbonate product is immersed in carbon tetrachloride, and is injection molded by high speed. The part has a tendency to crack, and the low speed does not crack.)

Under relatively slow filling conditions, the temperature difference of the stream, especially the temperature difference between the material before and after the gate, helps to avoid the occurrence of shrinkage cavities and depressions. However, due to the long filling time, it is easy to cause delamination and poorly welded welds, which not only affects the appearance, but also greatly reduces the mechanical strength.

When the high-speed injection is carried out, the flow speed is fast. When the high-speed filling is successful, the melt quickly fills the cavity, the material temperature drops less, the viscosity decreases less, and the injection pressure can be used, which is a hot charge. Modal potential. High-speed filling can improve the gloss and smoothness of the parts, eliminate the seam line phenomenon and delamination, shrink the small depression, uniform color, and ensure the fullness of the larger part. However, it is easy to produce fat or foaming of the product or yellowing of the workpiece, or even burn the zoom, or cause difficulty in demoulding, or uneven filling. For high-viscosity plastics, it is possible to cause the melt to rupture, causing cloud spots on the surface of the part.