Influence of the cutting edge radius on surface integrity in hard turning of roller bearing inner rings

Hard turning is used as a finishing process to machine hardened parts with very high accuracies. During the last decades it asserted as an alternative to conventional grinding processes due to higher flexibility and productivity. Furthermore, hard turning also increases positive effects on the surface integrity compared to grinding processes. Process parameters such as cutting speed, feed and cutting edge geometry influence the effect on subsurface area as well as the surface roughness. Many researchers have been analyzing these effects during the last years. However, they all cover one or two aspects of the surface integrity. Due to the fact that all researchers applied different experimental conditions it is almost impossible to compare the effects of hard turning on the surface integrity. The presented paper covers the effects of cutting speed, feed and cutting edge radius on the main factors of surface integrity residual stress, roughness, microstructure and hardness of roller bearings in a summarizing overview to identify the optimal parameter values for machining roller bearings with an increased endurance. Hard turning tests are conducted and the effects on residual stresses, surface roughness, hardness and white layers are analyzed. This overall view on surface integrity of roller bearings is necessary to improve the endurance of bearings due to a specific surface integrity design. The interactions between the surface integrity and the expected resulting endurance are discussed at the end of this article.