Protection of fasteners in aircraft construction
In the collaborative project "InBe-KoVer", which was successfully completed in 2021, Fraunhofer IFAM, Ingenieurbüro Tank GmbH, and other partners from industry worked on a local pretreatment and sealing of fasteners for the aging protection of CFRP metal structures and safety-relevant contacts in aircraft construction. The aim was to contribute to quality-assured, automated, and environmentally friendly aerospace manufacturing and repair. Fraunhofer IFAM has been involved in researching and improving the treatment and sealing homogeneity on different fasteners.
Safe processes for protecting fasteners - low-emission and resource-saving
The protection of fasteners (e.g. rivets) from corrosive media by means of closed paint coatings is a structurally and safety-relevant process, especially in CFRP-metal composite designs. Currently, the corresponding fasteners in aircraft construction are manually pretreated by solvent cleaning, mechanical activation and renewed solvent cleaning and sealed with paint by brush application. This involves many risks with regard to the quality of the processes and thus the safety of the aircraft. In addition, the current state of the art involves high consumption and disposal of solvents that are hazardous to health and the environment, which significantly increases the carbon footprint of aerospace manufacturing processes.
The project objective was to design a low-emission, resource-saving and safe process for the protection of fasteners. For this purpose, the combination of a local, suction-assisted, encapsulated and robust blasting process for cleaning and an automated application of sealing lacquers was researched. In addition to improved quality of aging protection, worker exposure to dust and solvents can be avoided, ergonomics improved, and paint quantities reduced. The targeted blasting and sealing techniques were successfully tested using the specified test geometries of application-relevant fasteners and on real aerospace components. The surface analytical investigations and aging tests carried out on the fasteners showed a significant improvement in adhesion formation and media resistance of the applied sealant as a result of the upstream, adapted blasting pretreatment. Thus, a sufficient preservation of the fasteners against the aging and corrosion phenomena can be expected.
The project was funded by the German Federal Ministry of Economics and Climate Protection (BMWK) as part of the research program "Aeronautics Research and Technology LuFo V-3, Program Line (B) SMEs" (funding code: 20Q1723 A/B). The project partners would like to thank the Deutsches Zentrum für Luft-und Raumfahrt e.V., the Project Management Agency for Aeronautics Research on behalf of the BMWK for the financial support and organizational supervision of the project. Thanks are also due to Airbus, Mankiewicz and Premium-Aerotec for the samples provided, support with regard to content and constructive discussions.