The conventional injection molding process can be divided into a filling process for controlling the melt inlet speed and a pressure holding process for controlling the melt inlet pressure to feed the plastic cooling shrinkage. The inlet velocity of the melt during the filling process is constant, and as the filling process progresses, the flow resistance of the melt in the cavity gradually increases. As a result, the melt inlet pressure is also prone to increase, with a higher peak at the inlet pressure at the end of the filling.
Due to the effect of high pressure in the cavity, not only the melt overflow, the mold increase and other undesirable phenomena, but also the internal stress of the plastic parts, the plastic parts are prone to warpage and deformation after demolding. It is difficult to meet the high requirements for the shape accuracy and dimensional accuracy of plastic parts, and it is prone to cracking during use.
In order to reduce or avoid the internal stress generated by the plastic during the filling process due to the high cavity pressure, the deformation of the plastic part is limited to a lower range. The filling should be done with the minimum pressure required to fill the plastic parts, thus reducing the pressure in the cavity.