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.
The surfaces of molds and dies need to present a good quality because their roughness profiles are transferred to either cast or formed products. Dies and molds are frequently made of complex surfaces, and consequently, an adequate milling strategy is important to result in a proper workpiece surface. To evaluate the adequacy of a surface to be used as forming tool involves the use of roughness parameters like S a , S sk , S ku , S p and S v. These parameters influence some surface properties like wear resistance and lubrication capacity. In this work, different tool paths of milling and turning processes were chosen to machine a typical spherical surface used as die (punch) of hot stamping, in order to analyze the surface parameters S a , S sk , S ku , S p and S v of hardened steel samples. The used milling strategies were circular (upward and downward), radial (upward and downward), parallel contours and spiral (upward). Punches machined by all strategies were submitted to thermochemical treatments, plasma nitriding and nitrocarburizing Tenifer ® process. The cited roughness parameters were measured in both moments, before and after the thermochemical treatments. There was similarity between milled and turned results, and thermochemical treatments presented significant influence on measured surface parameters. Machining marks were smoothed by thermochemical treatments which altered surface parameters. Thermochemical treatments effects were affected by the combination of machining marks and micro-burrs from machining processes. All tests resulted in S ku parameter either close or above 3. At 45° position of the workpiece, plasma nitriding tended to decrease roughness S a , S p and S v values and present positive values of parameter S sk. Nitrocarburizing process tended to increase roughness S a , S p and S v values and present negative values of parameter S sk , while not treated samples presented positive and negative S sk values, depending on the machining strategy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.