Relevance of roughness parameters of surface finish in precision hard turning

Precision hard turning is a process to improve the surface integrity of functional surfaces. Machining experiments are carried out on hardened AISI 52100 bearing steel under dry condition using c-BN cutting tools. A full factorial experimental design is used to characterize the effect of cutting parameters. As surface topography is characterized by numerous roughness parameters, their relative relevance is investigated by statistical indices of performance computed by combining the analysis of variance, discriminant analysis and the bootstrap method. The analysis shows that the profile Length ratio (Lr) and the Roughness average (Ra) are the relevant pair of roughness parameters which best discriminates the effect of cutting parameters and enable the classification of surfaces which cannot be distinguished by one parameter: low profile length ratio Lr (Lr = 100.23%) is clearly distinguished from an irregular surface corresponding to a profile length ratio Lr (Lr = 100.42%), whereas the roughness average Ra values are nearly identical.