Surface Integrity Aspects of Milled Large Hardened Gears

With the rising performance of wind turbines the requirements for large scale gears are growing. Due to the bigger loads based on the higher megawatt output per turbine gears especially at slewing bearings need to be hardened. Rising demands for better gear qualities and higher loads require a hard machining of these hardened gears. The development of special cutting materials for geometrically well-defined cutting edge processes enables the manufactures to mill these gears in hardened condition on standard milling machines. The process of milling hardened gears needs control of the surface integrity of the tooth flanks. The generation of white etching areas must be avoided and can be influenced by process parameters (e.g. cutting speed and feed rate). Preferably compressive residual stresses should be generated in the surface and sub-surface of the tooth flank. The paper describes the potentials of milling theses hardened gears instead of grinding and reveals the generated surface integrity state.