Tool nose radius effects on finish hard turning

Tool nose radius effects on finish turning of hardened AISI 52100 steels have been investigated. Surface finish, tool wear, cutting forces, and, particularly, white layer (phase transformation structures) were evaluated at different machining conditions. Results show that large tool nose radii only give finer surface finish, but comparable tool wear compared to small nose radius tools. Specific cutting energy slightly increases with tool nose radius. For new tools, white layers only occur at aggressive feeds (=0.3 mm/rev) and small nose radius results in deeper white layers. For worn tools, white layers appear even at mild feeds (0.05 mm/rev), but in contrast, large nose radius leaves deeper white layers. Smaller tool nose radius gives larger uncut chip thickness, and thus, greater shear plane heat source that may induce deeper white layers for new tool conditions. For worn tools, where the wear-land sliding is the major heat source, temperature analysis at machined surfaces reveals that the larger the tool nose radius, the deeper the temperature penetration due to a shorter transition-material zone from the cutting edge to the final machined surface.