Surface roughness in hard turning of EN 100Cr6 with coated PCBN cutting tools at micro cutting depths

This study addresses a critical aspect of hard turning—surface roughness at shallow depths of cut comparable to the cutting edge radius—by analyzing the influence of cutting parameters on surface integrity. Its findings are essential for optimizing finishing operations, as they highlight the importance of considering the cutting edge radius when determining minimum machining allowances. To estimate the minimum undeformed chip thickness, experiments were carried out on EN 100Cr6 hardened steel (60 HRC) using both free and constrained cutting methods, across two cutting speeds and three depths of cut. Advanced analysis of high-resolution 3D surface data with nonlinear dynamic techniques enabled the calculation of correlation entropy, correlation dimension, and noise levels, offering deeper insight into the mechanisms affecting surface quality. The findings confirmed that surface profiles exhibit a deterministic nature, as evidenced by multifractal spectrum analysis. Reducing the cutting depth led to increased peak density and surface complexity, while higher cutting speeds resulted in more ordered surfaces. Additionally, the relative length function revealed scale-dependent changes in surface complexity. Fractal dimension and correlation entropy emerged as effective diagnostic tools, offering insights into process stability and surface characteristics, thus providing a quantitative basis for optimizing finishing operations in hard turning.