Proportional control of injection speed is widely used by injection molding machine manufacturers.Although a computer controlled injection speed segmenting control system has long existed, the advantages of this machine setup have rarely been fully realized due to the limited information available.In this paper, the advantages of multistage velocity injection are systematically introduced, and its use in eliminating defects such as short injection, air entrapment and shrinkage is summarized.
The close relationship between injection velocity and product quality makes it a key parameter of injection molding.By determining the beginning, middle, and end of the filling velocity segments, and by achieving a smooth transition from one set point to another, a stable melt surface velocity can be ensured to produce the desired molecular minimum internal stress.
We recommend the following speed segmentation principle:
1) the fluid surface velocity should be constant.
2) quick shooting glue should be used.
3) the setting of injection speed should take into account the rapid filling in the critical area (such as the runner) and slowing down the speed at the inlet.
4) the injection speed should ensure that the cavity is immediately stopped after filling to prevent overfilling, flash, scorch and residual stress.
5) multi-stage injection can only be used when first-level injection cannot solve the problem.
The basis for setting the speed segments must take into account the geometry of the die, other flow restrictions and instability factors.The speed setting must have a clear understanding of injection molding process and material knowledge, otherwise, product quality will be difficult to control.Because melt velocity is difficult to measure directly, it can be calculated indirectly by measuring the forward speed of the screw, or the cavity pressure (to make sure the check valve does not leak).