Additive manufacturing can make aerospace greener

"How can aviation be made greener?" That's what Luke Schüller, research associate at Fraunhofer ILT, wonders in a technical article. He gives the answer: by using lightweight construction, additive manufacturing and new high-performance materials to meet stringent political demands for climate protection.

The laser powder bed fusion (LPBF) process, in which metal powder is fused layer by layer with the laser beam, plays a key role. This method allows users to produce complex and high-strength components that are not only lighter but also more resistant - crucial properties needed for tomorrow's aerospace.

Fraunhofer ILT is developing special powders as part of the TIRIKA research initiative (Technologies and Innovations for Resource-saving, Climate-friendly Aviation) of the Federal Ministry for Economic Affairs and Climate Action. The initiative focuses on the use of hydrogen as an emission-free energy source for aviation. Together with material manufacturers, the experts have developed powders that meet the aviation industry's high requirements for hydrogen engines. The experts have also developed LPBF processes. They do this for materials that are commercially available. They have been validated in cooperation with the partners using various test procedures.

"Through targeted modifications in the LPBF process, we can now achieve a relative component density of more than 99.5 per cent and a high build-up speed of more than 100 cm³/h," Schüller explains. The aluminium alloys are not only light, but they also have high strength. Moreover, they are resistant to hydrogen. It is an element that can cause embrittlement and material fatigue at high temperatures and pressures. This makes these alloys ideal candidates for use in future emission-free hydrogen engines. Moreover, thanks to the uniform laser melting process, the new special powders make it possible to generate complex geometric shapes and functional structures that cannot be made with conventional processes such as casting or forging.

During the production process, a precise sensor system detects artefacts up to a size of 0.4 millimetres directly in the powder bed and during the melting process. This minimises time-consuming subsequent inspections and significantly increases production efficiency.

Advanced processes, however, affect not only the quality and efficiency of production, but also their carbon footprint. Fraunhofer ILT uses life cycle assessment (LCA) to evaluate the environmental friendliness of additive manufacturing processes. This looks at the entire life cycle of a component - from raw material procurement to production and recycling. "For us, life cycle assessment is an indispensable tool to evaluate the environmental impact of products throughout their life cycle and identify sustainable alternatives," says Dr Tim Lantzsch, head of the Laser Powder Bed Fusion department at Fraunhofer ILT. However, to effectively design this comprehensive process, research needs to collect high-quality and meaningful data early on in the digital value chain.

Three main arguments argue in favour of this initially very difficult path. These data enable researchers to design start-up processes for new products faster and more efficiently (1). They support researchers in evaluating quality, cost, energy and resource consumption in the production cycle (2). And they contribute to greater transparency in processes and thus to optimising the entire production chain (3).
The results of LCA analyses show that, despite the relatively high energy consumption during the LPBF process, the ecological footprint of additive manufacturing is significantly smaller than that of conventional production methods. 3D printing is therefore particularly suitable for repairing parts because it minimises material loss and saves resources.

Additive processes are also the focus of the EU project ENLIGHTEN (European iNitiative for Low cost, Innovative & Green High Thrust ENgine Project). That project started in November 2022. It is managed and coordinated by the Ariane Group. Since the start of the project, 18 partners from eight European countries have had one goal in mind: to develop cost-effective and eco-friendly rocket engines that work with bio-methane and green hydrogen, among others. The new eco-motors are intended to power Europe's next generation of reusable rockets, thus strengthening Europe's competitiveness in the global aerospace sector.

This is where the Aachen Institute comes in around the corner. As part of the project, experts from the LMD group Additive Manufacturing and Repair are developing a process to produce rocket parts more efficiently and accurately using laser material deposition (LMD). "The special feature is that we are using LMD to dramatically improve the speed and cost-effectiveness of manufacturing new types of rocket nozzles," explains Min-Uh Ko, group leader of Additive Manufacturing and Repair LMD at Fraunhofer ILT. "Apart from the large installation space, the investigated design has exceptionally filigree and thin-walled cooling channels that can only be generated with great difficulty using conventional manufacturing routes." The goal by the end of the project in October 2025: LMD production of a nozzle for use in the next generation of rockets in the Ariane programme and construction of a full-scale demonstrator.

The experts approach the project in an integrated way. By the end of the project, they want to develop a reliable, controlled production process, including quality assurance for series production. An inline system will use sensors to monitor the entire process, detect and correct deviations in the process and ensure consistently high component quality. Min-Uh Ko: "If we have successfully developed the process and the demonstrator, it will mean a breakthrough. With our results, we can enable the industry, as a supplier to the aerospace industry, to produce similarly large, complex and filigree structures on their own systems via LMD in the future."

Opening photo: "The special thing about LMD is that it dramatically improves the speed and cost-effectiveness of manufacturing new types of rocket nozzles." Min-Uh Ko, group leader of Additive Manufacturing and Repair LMD at Fraunhofer ILT. (Photo: Fraunhofer ILT, Aachen, Germany / Ralf Baumgarten.)

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