Development of an injection strategy for cascade injection moulding to achieve a constant melt front velocity.

• Applicant: Professor Dr.-Ing. Christian Hopmann
• Subject Area: Plastics Engineering
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 560493839

Cascade injection moulding is the process used for components with high surface quality requirements and large flow path/wall thickness ratios. The surface quality is significantly influenced during the injection phase. Due to the pressure peaks that occur as a result of the opening and closing of the hot runner valve pins, it is more difficult to achieve a good surface quality than with moulds with only one gate per cavity. Due to the complex interrelationships in cascade injection moulding, especially between the injection volume rate profile set on the machine and the interaction of the individual pin strokes, the process setup is very complex and involves a large number of experimental trials. Therefore, a methodology for deriving the injection strategy for cascade injection moulding is to be developed, which results in good component qualities independently of the machine operator's experience and without extensive trials. In order to achieve a uniformly high surface quality along the entire flow path, a constant melt front velocity is to be achieved in the cavity. In a first step, the nozzle-specific injection volume rate profiles are determined using an automatable method, taking into account the cascade, in order to realise a constant target melt front speed in the cavity. Based on the necessary nozzle-specific volume rate profiles, the individual opening stroke profiles and the injection volume rate profile of the screw are calculated with the help of a process model. The process model takes particular account of the interaction between the individual hot runner nozzles. Experimental tests are used to validate and optimise the developed injection strategy for different geometries and material types. In addition, the effect of the injection strategy on the surface quality, such as gloss, roughness and molecular orientation in the surface layer, is investigated. Finally, the robustness of the process to process fluctuations is analysed in order to derive key figures for process monitoring of the filling phase of cascade injection moulding.

• DFG Programme: Research Grants