Laser micro structuring of multi-layer coatings on aircraft splines for optimization of the surface properties

In the aircraft industry spline-joints are used for the connection of subassemblies in geared turbofans. Besides the power transmission, spline-joints are used to compensate deviations in the shaft system, such as angular or axial misalignments. By decoupling the subassemblies, constraining forces are reduced, which affects the dimensioning of the surrounding components. Increasing the load capacity of spline-joints enables a lean and efficient design of the components. The wear behavior of such heavily loaded splines can be improved by multi-layered coatings deposited e. g. by physical vapor deposi-tion (PVD). Further improvements can be realized by an additional laser structured surface topology, which includes an arrangement of semi-spheres in the coating system with diameters in the micrometer range. These semi-spheres can either serve as a micro pocket for lubrications or are applied before the final coating step to be replenished with a hard lubricant layer. This paper addresses this subject by presenting the manufacturing process of splines with focus on the laser texturing process.