Development of a cavity pressure control for injection moulding by adjusting the cross-section in the hot runner

Abstract

Abstract Fluctuations in the injection moulding process are affecting component quality. A pressure control can be used to increase process consistency. However, current control systems cannot influence the melt flow in the mould specifically for individual cavities. Therefore, a control concept is being developed in which commercially available, servo-electrically driven hot runner valve pins are used to control the cavity pressure in the holding pressure phase. By varying the stroke, the pressure resistance in the hot runner and thus the pressure transfer into the cavity are influenced. A one cavity mould with two pressure sensors and a servo-electrical driven hot runner was used to evaluate the control setup, implementing a PID controller. The evaluation criterion for the setup is to what extent the reference curve measured in advance can be reproduced after provoked disturbance. The control calculates the difference between the actual pressure and the reference curve. The control compensates the pressure difference by a pin movement. The control concept can compensate for disturbances that do not change the material behaviour, such as changes in holding pressure. Changes in the material behaviour, for example due to fluctuations in the mould temperature, cannot be compensated due to the reference control.