Lightweight Construction Sustainable Lightweight Solutions for Aircraft Cabins

In the "STair" project, Diehl Aviation, Ensinger, ThermHex, and the Fraunhofer Institute for Microstructure of Materials and Systems IMWS are developing new thermoplastic lightweight components for aircraft cabins that can be processed faster and are more environmentally friendly.

Lightweight solutions are essential for aviation. Every kilogram of weight saved reduces fuel consumption and, consequently, emissions. This helps achieve sustainability goals while also minimizing the impact of rising CO₂ pricing. In the cabin, sandwich-structured components are often used for elements such as luggage compartments or galley walls: thin, solid face sheets enclose a lightweight core. This enables robust yet very light constructions. Currently, thermoset components with phenolic resin-based face sheets and a honeycomb core made of aramid paper dominate in this area.

Researchers at Fraunhofer IMWS have now developed the Thermoplastic Sandwich Moulding technology. This technology enables the use of thermoplastic plastics for such applications. Diehl Aviation Laupheim GmbH, Ensinger GmbH, ThermHex Waben GmbH, and Fraunhofer IMWS aim to demonstrate its feasibility by April 2027 in the "STair" project. "The advantages would be significant: thermoplastic systems can be processed much faster, with better energy and material efficiency. This is particularly relevant for the cabin, which is renewed multiple times over the lifecycle of an aircraft. They are also recyclable and do not require environmentally harmful solvents," says Dr.-Ing. Ralf Schlimper, who leads the subproject at Fraunhofer IMWS.

Save 30 percent energy compared to thermoset plastics

The targeted energy savings during processing amount to around 30 percent compared to the state-of-the-art and the use of thermoset plastics. Production waste is to be directly recycled in semi-finished product manufacturing by up to 80 percent. Solvent emissions during production are to be reduced by up to 80 percent.

To make these results possible, the first step is to adapt the Thermoplastic Sandwich Moulding technology to process high-temperature-resistant thermoplastic sandwich structures (HT-TP sandwiches), which are specifically designed to meet the requirements of the aviation industry. The method represents a very efficient and highly automated one-shot process combining thermoforming and functionalization via injection molding. However, the corresponding process steps (shaping, joining, and functionalization) must be further developed for the use of HT thermoplastic plastics.

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Components no heavier than thermoset solutions

"We will examine various components from the cabin, initially defining requirements and then developing and testing the corresponding solutions for semi-finished products, sample materials, attractive aesthetics of the components, as well as forming and processing procedures along different process routes. The goal is to establish a technology platform, also utilizing simulation tools. The components should be no heavier than current thermoset solutions and meet all existing aviation requirements so that the results can be quickly brought to market. Lastly, we are also considering accompanying life cycle analyses and recycling concepts," says Schlimper.

At Fraunhofer IMWS, the focus is primarily on researching efficient thermoforming processes. HT semi-finished products (flat sandwich panels with thermoplastic honeycomb or foam cores and face sheets made of fiber-reinforced thermoplastic plastics) are to be processed into 3D-shaped components and component parts. For this purpose, they are first heated and then quickly transferred into the forming tool, which is to be developed as part of the project. There, 3D thermoforming takes place at temperatures above 200°C (approx. 392°F). In addition to the high temperature, a challenge lies in the complex processing behavior. The lightweight core is to be largely preserved across the surface, while monolithic end areas on component edges are to be achieved, requiring the complete melting and compression of the core. The project is also investigating hybrid sandwich structures with a combined core (e.g., a honeycomb core in the surface area and a foam core in geometrically more complex component regions). This increases the complexity of both processing procedures and the analysis of material behavior.

"We have extensive prior knowledge for this process, including supporting modeling approaches and the appropriate technical equipment. This allows us to systematically study aspects such as component geometry, edge and rim finishes, as well as interfaces with functional elements," says Schlimper. The institute also has suitable methods for analyzing operational and long-term behavior, such as strain measurements, morphological investigations with X-ray CT, and accelerated aging tests. Additionally, the project team will explore the possibilities of material recycling, such as the properties of components containing recyclates from production scraps.

More sustainable solutions for cabin components in aircraft

If the project partners are successful, significantly more sustainable solutions for cabin components in aircraft will become possible. "With our approach, emissions can be significantly reduced both during production and at the end of the lifecycle, while still meeting aesthetic and functional requirements," says Schlimper. "A major advantage is that our collaboration covers all aspects of the value chain, from material production to component manufacturing. This promises good chances of success."

Dr.-Ing. Jochen Pflug, Managing Director of ThermHex Waben GmbH: "Step by step, we are transferring our recyclable lightweight thermoplastic honeycomb sandwich materials with 'STair' from the automotive to the aerospace industry. In doing so, we are successfully combining opportunities for cost reductions and production automation with the industry's required performance targets. I am enthusiastic and grateful for the opportunity to further develop our products together with strong partners."

The project is funded by the Federal Ministry for Economic Affairs and Energy (BMWi) as part of the Aviation Research Program (LuFo Klima VII-1).