High-tech repair for fiber composite materials
In order to be able to steadily improve the performance of its products, the aerospace industry is constantly developing improved structural materials. In particular, high-tech composite materials such as carbon fiber composites (CFC) are becoming ever more important in the construction of aircraft. Increased use of fiber composites in modern aircraft construction is being driven forward by their favorable strength-to-mass ratio, fatigue strength, resistance to corrosion and their malleability. On the other hand, up to now the complexity and expense of repairing composite materials have cancelled out some of the considerable savings possible in construction.
Under a multi-year research project running from January 2009 to April 2012, Lufthansa Technik AG has been working with five cooperation partners – iSAM AG, Cassidian, GOM - Gesellschaft fur Optische Messtechnik mbH, Electro Optical Systems (EOS) and Eurocopter – on the development of a generally applicable process chain for the rapid, automatable and reproducible repair of high-performance fiber composite materials. The project is centered around the repair of panels on monolithic and sandwich structures. The future "Rapid Repair" method will primarily be used on aircraft fuselage and wing structures, but it can also be applied to helicopter rotor blades. A patent application has already been submitted for the present project, which is supported by the Federal Ministry of Economic Affairs (BMWi).
This is how it works:
The process which is the subject of the research project kicks in after the damage has been detected and the affected component has been cleaned. The first step is to scan and capture the surface contour of the component by means of strip light projection. The individual surface and contour details have to be gathered for each damaged component as every instance of damage has its own unique dimensions. The scanning and capture processes are performed to the nearest hundredth of a millimeter.
Special software that enables a highly customized scarf joint to be fitted to the defective area was developed for the project. A computer calculates the trajectories to be milled in the material so as to achieve the optimally prepared and customized bonding surfaces. The milling robot used has a three cubic meter working area so as to be able to handle particularly large components. It is installed in a separate milling room and is controlled from an adjoining room so that the fine dust generated during milling can be isolated and safely extracted.
After milling, the new component is scanned once again so that the quality of the scarf joint can be assessed. This entails overlaying the available data for the scarf joint and the strip light projection to enable any deviations to be spotted more easily. At the same time the data obtained in this way is also used for the further development of new repair tools.
The pre-cuts of composite layers are then created using a ply cutter that is rather like a cutting machine for textile fabric, before being applied to the component to be repaired. This is carried out with 100 percent accuracy. The individual layers of the cut-to-size panel are bonded with the primary structure and then cured as required.
As most of the work in "Rapid Repair" is performed by robots, for the time being the method can only be applied at a fixed installation. Hence, even as the existing research project continues, a three-year follow-up project "Caire" has been planned to start in April 2012 with the aim of enabling mobile application of the new repair method. In this way in the future the technicians will be able to take their equipment out to the damaged customer aircraft and repair it directly on site. This will obviate the need for time-consuming removal of the affected parts and modules.
Compared with the manual process used up to now, the future automated repair method will cut the repair time by about 60 percent. In this way with the new method Lufthansa Technik is paving the way for reducing the repair costs and thus supplying an important argument for increasing still further the use of fiber composite materials in aircraft construction.