Lightweight Construction Sustainable Lightweight Solutions for Aircraft Cabins

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Fraunhofer-Institut für Mikrostruktur von Werkstoffen und Systemen IMWS

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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 and minimizes the impact of rising CO2 pricing. For elements such as overhead compartments or galley walls, sandwich components are often used in the cabin: thin, sturdy face sheets enclose a lightweight core. This enables robust yet very lightweight constructions. Currently, thermoset components with phenolic resin-based face sheets and a honeycomb core made of aramid paper dominate this field.

Researchers at the Fraunhofer IMWS have now developed the Thermoplastic Sandwich Moulding technology. This technology enables the use of thermoplastic plastics for such applications. Proof of concept is to be provided by Diehl Aviation Laupheim GmbH, Ensinger GmbH, ThermHex Waben GmbH, and Fraunhofer IMWS by April 2027 in the "STair" project. "The advantages would be significant: Thermoplastic systems can be processed much faster and with better energy and material efficiency. This is particularly relevant for the cabin, which is renewed multiple times during 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 Thermosetting Plastics

The targeted energy savings in processing is around 30 percent compared to the state of the art and the use of thermosetting plastics. Production waste is expected to be directly recycled in semi-finished product manufacturing by up to 80 percent. Emissions from solvents during production are expected to decrease by up to 80 percent.

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

Components No Heavier Than Thermosetting Solutions

"We will examine various cabin components for this purpose, first define requirements, and then develop and test the corresponding solutions for semi-finished products, sample materials, attractive aesthetics of components, as well as forming and processing processes along different process routes. The goal is to establish a technology platform, also utilizing simulation tools. The components should be at most as heavy as current thermoset solutions and meet all existing aviation requirements so that the results can be quickly brought to market. Lastly, we are also focusing on accompanying lifecycle 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 a thermoplastic honeycomb or foam core and face sheets made of fiber-reinforced thermoplastic plastics) are to be processed into 3D-formed components and component parts. For this purpose, they are first heated and then quickly transferred into a forming tool, which is to be developed within the project. The 3D thermoforming takes place at temperatures exceeding 392 °F. In addition to the high temperature, the complex processing behavior poses a challenge. Most of the lightweight core is intended to remain intact in the flat areas, while monolithically tapered areas at the component edges are to be realized, requiring complete melting and compression of the core. The project also investigates hybrid sandwich structures with a combined core (e.g., honeycomb core in flat areas and foam core in geometrically more complex component regions). This makes processing methods and the study of material behavior even more complex.

"We have extensive prior knowledge for this process, including supportive modeling approaches, and the appropriate technical equipment. This allows us to systematically investigate aspects such as component geometry, edge and border finishes, and interfaces with functional elements," says Schlimper. The institute also has suitable methods for analyzing usage and long-term behavior, such as strain measurements, morphological studies 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 trimming residues.

More Sustainable Solutions for Cabin Components in Aircraft

If the project partners are successful, significantly more sustainable solutions for aircraft cabin components will become possible. "With our approach, emissions can be substantially reduced both during manufacturing 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 prospects for 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 successfully combine opportunities for cost reduction and production automation with the required performance goals of the sector. I am excited 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).

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