Repairs now also possible upside down

Research project on the repair of composite materials takes the next big step

The fuselage and wing structures of modern widebody aircraft consist largely of high-performance fiber-reinforced composites (FRCs). For a long time, determining and repairing damage to the aircraft's skin sections required a great deal of effort, whether the work was carried out in the field or in a workshop. That will now change, thanks to Lufthansa Technik: As early as 2012, the "Rapid Repair" research project developed a stationary scarf joining robot to enable a continuous process chain for rapid, automated and reproducible repairs of FRC materials. The follow-up project, "Composite Adaptable Inspection and Repair" (CAIRE), succeeded in further enhancing the technology of the stationary scarf joining robot to allow for mobile repairs. 

The mobile robot is even able to recognize free-form 3D surfaces. To make a scarf joint, the robot is placed on a fixing device attached to the component with suction cups. Specially developed software allows the mobile robot to process 1,000 x 1,000 millimeter surfaces and thick FRC structures such as wing connection areas. For this purpose, it scans the damage, identifies the surface and calculates both the form of the scarf joint and the milling path before cutting out the damaged material. Afterwards, the repair layers are cut to size and inserted into the 3D scarfing surface created by the robot. The newly inserted part is then manually glued to the fuselage and cured.

After extensive tests using a robot demonstrator on individual components as well as on entire aircraft, the team was able to successfully conclude the "CAIRE" research and development project. Mechanical trials during the project proved that the procedure not only enables reproducible repairs of damages but also increases bonding strength. This is a major step toward carrying out adhesive-based repairs on critical structures made of fiber-reinforced composites. With the help of the new robot, mobile service teams are able – now even on wing – to diagnose and repair large areas of damage on the wings and fuselage.

The preparations for the introduction of a fully industrialized system are currently in full swing at Lufthansa Technik. For example, two patent applications have already been filed for the development: The first is for the positioning mechanism that enables a single employee to flexibly and precisely position the scarf joining robot anywhere on the aircraft – whether from the side, from above with an overhead crane or even upside down with the help of hoisting gear. The second patent application describes a device and a procedure, which allow the milling accuracy of the robot to be increased considerably.

Lufthansa Technik's current plan is to put the stationary systems into operation by fall 2018. The first system will be used by the Airframe Related Components (ARC®) unit for structural components. In parallel, Lufthansa Technik is working on industrializing the mobile system. Targeted use of the scarf joining robot not only results in cost and time savings; the new procedure also significantly increases quality, since it makes entirely new repair geometries possible.