The use of high-temperature thermoplastics in combination with an efficient forming process with direct functional integration makes it possible to produce even complex-shaped structural components for aerospace applications in a cycle time of less than four minutes. This is the result of a publicly funded cooperation project involving Neue Materialien Bayreuth GmbH.
Are laminates made from UD tapes in a thermoplastic matrix with directly injection-moulded functional integration also suitable for the aviation industry for the production of complex formed structural components? The recently successfully completed HELUES joint project addressed this question.
The focus was on a one-step process in which functional elements, such as reinforcing ribs and screw domes, are applied directly after thermoforming the thermoplastic laminate via an injection molding process (one-step overmolding). This process combination of forming and functional integration allows the entire component to be manufactured in a single step, eliminating the assembly steps of conventional processes. At the same time, the use of the thermoplastic material, which unlike thermosets does not require a curing process, also shortens the process chain. In this way, the cycle time for the production of high-quality structural components can be significantly reduced, thus demonstrating a high potential for cost reduction.
In the joint project, this process was transferred to the production of a technology demonstrator made of UD tapes with a matrix of carbon fiber-reinforced polyether ketone ketone (PEKK), which corresponds to an assembly in an aircraft emergency exit door. This technology demonstrator could be manufactured with cycle times of less than four minutes, which represents a significant advance in the efficiency and cost-effectiveness of over-molding technology for aviation applications.
NMB’s work focused on the development of a process chain for the single-stage forming and over-molding process – consisting of a handling system, IR heating system and 450 t injection moulding machine – and the subsequent manufacture of the technology demonstrator.
Furthermore, the limits of the deformation of laminates based on PEKK-CF were investigated in preliminary tests on a laboratory scale, focusing on the influence of the process control on the component properties. The investigations into the bonding strength of the injection-moulded functional elements concentrated on the mechanical properties of the connection between the injection-moulded ribs and the thermoformed UD laminates, whereby the bonding behaviour under various process parameters was analyzed in detail. The bonding of rear ribs, which were injected through openings in the laminate, was also investigated.
The knowledge gained from these material tests on process and design limits was transferred to the process control during the manufacture of the demonstrator component and to the development of the demonstrator tool. The consortium leader Siebenwurst was responsible for the design and construction of the complex forming and back-injection tools with high-temperature requirements and the development of the demonstrator component to a production-ready state.
The joint project “HELUES – Highly efficient aerospace fibre composite components made of unidirectional single layers and injection moulding functionalization” was funded by the Bavarian State Ministry of Economic Affairs, Regional Development and Energy (StMWi) over a period of 36 months. The project partners were Christian Karl Siebenwurst GmbH & Co. KG and Neue Materialien Bayreuth GmbH with the associated partners Airbus Helicopters Deutschland and Hexcel Composites GmbH.