Landing gear leg coating removal

Now largely automated

The landing gears of modern commercial aircraft have to satisfy an exacting set of requirements. The landing gear not only bears the weight of the aircraft but also enables it to move on the ground. During landing, the relatively high shock load is absorbed by the landing gear shock absorbers and kept away from the fuselage. The landing gear of an aircraft includes the wheels with tires, rims and the brakes installed in them, along with the wheel suspensions on shock absorber struts and shock struts.

To satisfy the stringent aviation technical standards, landing gears are required to have regular, comprehensive overhauls. At defined intervals they are inspected for possible material defects and to ensure they are fully functional. In order to be able to inspect the individual layers of material on the landing gear in the course of a general overhaul and diagnose any possible damage, the individual landing gear components have to first be stripped and de-coated. Up to now they have been de-coated both on the outside and also inside the drilled holes by manual stripping with plastic blast medium (Poly Plus shot peening procedure). This treatment is labor-intensive, time-consuming and expensive, and it also exposes the operators involved to considerable physical stress. 

Under the "Removal of component coatings" research and development project Lufthansa Technik is developing a new procedure for automating this treatment process. The aim of the project is to lay the groundwork from the technical point of view that will enable components made from different materials (heat-treated high-strength steel, lighter materials such as aluminum, titanium and magnesium and light metal alloys etc.) and with different geometries to be identified and de-coated in an automated process. Further objectives are to increase process reliability by incorporating quality control into the process and, by dispensing with chemical pretreatments, to conserve resources.

Together with its project partner, the Institute of Automation Technology, Helmut Schmidt University Hamburg, Lufthansa Technik has already achieved some preliminary successes. Thus, using intelligent algorithms and modern image processing techniques, it has already succeeded in developing a material identification and positioning control system. At the same time new algorithms and a sensor system for reliable surface inspection have also been developed. As a result it will be possible in the future to identify and objectively classify surface segments that have to be machine-finished more quickly.

The next step in this project supported by the Federal Ministry of Education and Research, which has been running since January 2011 and is due to finish in December 2013, will be to integrate the developments into a unified, robot-based system. The 8-access gantry robot is programmed manually for each landing gear component on a one-off basis using a joystick. In the course of this programming operation the robot makes a mental note of all the motion paths. All other paths, for example those involved in surface inspection, are then worked out automatically. In the future components that have to be examined on a recurring basis will just have to be clamped in the appropriate jig and the relevant processing program called up. The component will then be stripped from the outside totally automatically. De-coating of the component from inside will be carried out during the automation process using an inside blasting jet about two meters long.

This significant increase in the extent of automation means that the operators no longer have to perform a time-consuming job that exposes them to considerable physical stress. In this way more components can be handled in the same time by the same number of operators. In addition the new, largely automated procedure conserves resources and increases quality. Once the "Removal of component coatings" research and development project has ended and the procedure has become established for landing gear components it is possible that in future all coated and lacquered large components could be de-coated in the same way.