As part of the research project, a control strategy for cascade injection molding is being developed, based on servo-electrically driven hot runner pins. The goal is to enhance process consistency and sustainably improve component quality through precise control of the mold cavity pressure.
Cascade injection moulding is the preferred process for the production of components with long flow paths and without visible weld lines. In addition to shrinkage and warpage, which can also occur as component defects in standard injection moulding, flow marks, overpacking in the middle of the component and, in the case of light applications, polarisation also occur as component defects in cascade injection moulding due to the multiple gates. Like the conventional injection moulding process, cascade injection moulding is subject to unfavourable influences due to the processing of different material batches, which change component quality.
© IKVThe aim of the research project KaskaRe is to develop a cavity pressure control system for cascade injection moulding in order to increase process consistency and component quality. The control system is to compensate viscosity fluctuations that occur, for example, due to the processing of different recyclate proportions.
A prior research project has demonstrated that the cavity pressure can be controlled by the movement of the hot runner shut-off needles on a single mould. Fluctuations in the process can be compensated and the process consistency is increased.
Building on this previous project, KaskaRe starts by optimising the geometry of the shut-off needles in order to increase the control quality. To this end, the influence of different opening strokes of a shut-off needle on the pressure loss in the hot runner investigated varying the hot runner geometry and the system behaviour is simulated. Subsequently, the needle geometry is varied in order to adjust the pressure losses over the largest possible opening stroke at low plastic melt shear. This creates the basis for a sensitive control. The most suitable needle geometry is validated experimentally.
In the further course, a control strategy is to be developed with the adapted needle geometry, which controls the cavity pressure following the filling phase at a sensor position by adjusting the opening strokes. For this purpose, the influence of the various independent needle movements on the cavity pressure is analysed and mapped in a substitute system. From this, a weighting function is derived, which should subsequently enable simple parameterisation of the control. Furthermore, the control system is implemented and tested in practice. The control strategy is optimised so that viscosity fluctuations of the plastic melt can be compensated. At the end of the project, the developed control strategy will be transferred to another specimen geometry in order to be able to assess the influence of the control on the component quality and the process constancy independently of the geometry.
Project Data and Funding
We would like to thank the AiF for funding the IGF research project (funding code 22805 N) and the project partnersfor their cooperation.
Project duration: 01.03.2023 – 28.02.2025
Project Partners
