3D printing for a green aviation and aerospace industry

The European Commission's targets are ambitious: the ReFuelEU Aviation regulation stipulates a 60 per cent reduction in CO₂ emissions from aviation by 2050 compared to 1990. A comprehensive EU Space Law (EUSL) is also planned, including rules on the sustainability of space activities. The aerospace companies are receiving support from the Fraunhofer Institute for Laser Technology ILT in Aachen and its new additive manufacturing processes, which significantly improve the ecological footprint and reduce production costs.

‘How can aviation be made greener?’ Luke Schüller, research associate at Fraunhofer ILT, asks in a technical article, and he also provides the answer: implement strict political climate protection targets with lightweight construction, 3D printing and new high-performance materials.

The LPBF (Laser Powder Bed Fusion) process, in which metal powder is fused layer by layer with a laser beam, plays a major role. This method makes it possible to manufacture complex and high-strength components that are not only lighter but also more resilient – important properties for tomorrow's aviation.

Fraunhofer ILT is working on the development as part of the research initiative TIRIKA (Technologies and Innovations for a Resource-Conserving, Climate-Friendly Aviation) of the Federal Ministry for Economic Affairs and Climate Protection. The focus is on the use of hydrogen as an emission-free energy source for aviation. Together with material manufacturers, the experts have developed special powders that meet the high requirements of the aviation industry for hydrogen propulsion. The experts have developed LPBF processes for commercially available materials and finally validated them in various test procedures in collaboration with the partners.

‘Through targeted process adjustments in the LPBF process, we can achieve a relative component density of over 99.5 per cent and a high build-up rate of more than 100 cm³/h,’ explains Schüller. The aluminium alloys are not only light and high-strength, but also resistant to hydrogen, which can lead to embrittlement and material fatigue at high temperatures and pressures. This makes them ideal candidates for use in the zero-emission hydrogen engines of the future. What's more, thanks to the uniform laser melting process, the new special powders enable complex geometries and functional structures that cannot be achieved using conventional methods such as casting or forging.

During the manufacturing process, a precise sensor system detects artefacts down to a size of 0.4 millimeters directly in the powder bed and in the melting process. This minimises the need for time-consuming downstream testing and significantly increases production efficiency.

However, advanced processes not only influence the quality and efficiency of production, but also its ecological balance. The Fraunhofer ILT relies on life cycle assessment (LCA) to evaluate the environmental friendliness of additive manufacturing processes. This approach considers the entire life cycle of a component – from raw material procurement to manufacturing and recycling. ‘For us, life cycle assessment is an indispensable tool for evaluating the environmental impact of products over their entire life cycle and identifying sustainable alternatives,’ says Dr. Tim Lantzsch, head of the Laser Powder Bed Fusion department at Fraunhofer ILT. However, to make this comprehensive process effective, it is crucial to obtain high-quality and meaningful data at an early stage in the digital value chain.

There are three important arguments in favour of this initially very laborious approach: Firstly, data enables faster and more efficient design of start-up processes for new products. Secondly, it supports the evaluation of quality, costs, energy and resource consumption in the production cycle. Thirdly, it contributes to greater transparency in the processes and thus to the optimisation of the entire production chain.

The results of the LCA analyses show that despite the comparatively 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 components because it minimises material loss and conserves resources.

Additive processes are also the focus of the EU project ENLIGHTEN (European iNitiative for Low cost, Innovative & Green High Thrust ENgine Projekt), which was launched in November 2022 and is managed and coordinated by the Ariane Group. Since the project began, 18 partners from eight European countries have been working towards a single goal: to develop cost-effective and environmentally friendly rocket propulsion systems that run on biomethane and green hydrogen, among other things. The new eco-engines are designed to power the next generation of European reusable rockets, thereby strengthening Europe's competitiveness in the global space sector.

This is where the Aachen-based institute comes in. As part of the project, experts from the Additive Manufacturing and Repair LMD group are developing a process to manufacture rocket components more efficiently and precisely using laser material deposition (LMD). ‘What is special is that we are drastically improving the speed and cost-effectiveness of manufacturing novel rocket nozzles using LMD,’ explains Min-Uh Ko, group manager of Additive Manufacturing and Repair LMD at Fraunhofer ILT. ‘Apart from its large size, the design under investigation features exceptionally delicate and thin-walled cooling channels that can only be realised with great effort 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 true-to-scale demonstrator.

The conventional method used so far is not ideal: Because no company can offer all the different process steps in a local production facility, the components have to be transported to several locations. The resulting process chain leads to a time-consuming and costly production process that often takes several months. Jochen Kittel, project manager of the ENLIGHTEN project at the Fraunhofer ILT: ‘With our process technology, which eliminates many individual process steps, we not only achieve a significant cost reduction. At the same time, we significantly shorten the production time of a rocket nozzle.’

The experts are taking a holistic approach to the project: by the end of the project, a reliable, controlled manufacturing process including quality assurance for series production is to be developed. An inline system with sensors will monitor the entire process, detect and correct process anomalies, and ensure consistently high component quality. Min-Uh Ko: ‘If we successfully develop the process and the demonstrator, it will mark a breakthrough. With our results, we can enable industry to produce equally large, complex and delicate structures as a supplier to the aerospace industry in the future, using their own LMD systems.’