Cutting forces, surface roughness and tool life in high-speed milling of hardened steel convex surface

This paper presents a contribution to hardened tool steel milling studies. High-speed milling is largely utilized to substitute some EDM and polishing operations, mainly in finish machining of dies and molds made of hardened tool steel. Tool path and tool inclination are parameters used to identify adequate milling strategies, mainly to super finishing operations. Tool strategy is a very important variable in this kind of operations, since it may generate either long or short tool life, either low or high workpiece surface roughness. In this work, several milling experiments were performed in a circular convex AISI D6 hardened steel workpiece, having as input variables feed direction (upward and downward following the circular form of the surface) and tilt angle (tool inclination). Downward tool path resulted in longer tool lives, regardless the tilt angle utilized. Moreover, in upward tool path, workpiece surface roughness was not adequate to a process which aims to replace EDM. In downward tool path and tilt angle 0°, workpiece surface roughness values were adequate to EDM substitution along the whole tool life and the ratio of axial and radial cutting force components was higher than in upward tool path, which was determinant to the generation of low values of surface roughness.