Effects of Tool Wear on the Surface Texture in Turning: A Feature Characterization Approach Based on ISO 21920-2

The surface texture of a turned component acts as a fingerprint of both the process parameters and the tool wear condition, imaging the cutting edge. Classical surface parameters such as $R_\mathrm{a}$ or $R_\mathrm{q}$ describe the topography only globally and allow no spatially resolved evaluation of the process-induced deterministic structures. This work investigates how far the feature characterization standardized in ISO 21920-2 makes this wear information accessible and physically interpretable. The database comprises roughness profiles of twelve AlTiN-coated carbide inserts (CNMG120408) machining normalized AISI 1045 steel, measured at nine wear states over the entire tool life, with three replicate profiles per state. The correlation of standardized field and feature parameters with crater wear, flank wear, and cutting time is first examined. Watershed segmentation is then adapted to extract the rotational tool grooves and evaluate their geometry statistically. A newly developed mean-feature approach decomposes the profile into a deterministic and a stochastic component. Wear-induced changes are almost entirely carried by the deterministic component, and within it by the trailing flank of the cutting groove. A comparison with confocal measurements confirms that the mean feature reconstructs the engaged cutting edge geometry, with the trailing-flank steepening attributable to notch wear on the secondary cutting edge. An exhaustive evaluation of more than 920,000 feature characterization combinations and multivariate models reveals that the groove-level mean maximum absolute gradient $\overline{R_\mathrm{dt}}_\mathrm{groove}$ alone explains 83-90% of the variance of the wear indicators, so that a single, physically motivated parameter suffices for robust wear estimation. A follow-up study will investigate inline monitoring using scattered light sensors.

Surface Topography as an Energy State: Hamiltonian Description of Functional Properties in Phase Space and Quantification via Optical Methods

The assessment of tribological processes necessitates comprehensive monitoring and interpretation of surface states, traditionally by topography height values and surface texture parameters. This paper proposes a phase space representation as generic interpretation of surfaces to enhance tribological assessments. By deriving distinctions between two-dimensional and three-dimensional manifolds from phenomenological thermodynamics, we demonstrate the existence of fractal dimensions on physical surfaces. Utilizing the smallest representable wavelength, a coordinate ensemble where each coordinate has a generalized degree of freedom and a differential amount across fractal dimensions is proposed. The metric is interpreted as a time coordinate, allowing the derivative to be seen as velocity. Through geometric dimension analysis, we derive a topographic Hamiltonian via generalized momentum. Each coordinate pair in the ensemble is assigned a location in phase space. Statistical considerations define a symplectic structure and phase space volume. As a use-case, a two-disc experiment demonstrates that topography changes under load can be understood as a self-organization process through thermodynamic reasoning. As a possibility for a direct assessment of the phase space of a surface for monitoring tribological processes, we propose the combination of topographic measuring systems with scattering light measurement. This multi sensor approach offers opportunities for optimizing performance in tribological applications.

Feature Characterization for Profile Surface Texture

Conventional field parameters for surface measurement use all data points, while feature characterization focuses on subsets extracted by watershed segmentation. This approach enables the extraction of specific features that are potentially responsible for the function of the surface or are a direct reflection of the manufacturing process, allowing for a more accurate assessment of both aspects. Feature characterization with the underlying watershed segmentation for areal surface topographies has been standardized for over a decade and is well established in industry and research. In contrast, feature characterization for surface profiles has been standardized recently, and the corresponding standard for watershed segmentation is planned to be published in the near future. Since the standards do not provide guidelines for implementation, this paper presents an unambiguous algorithm of the watershed segmentation and the feature characterization for surface profiles. This framework provides the basis for future work, mainly investigating the relationship between feature parameters based on feature characterization and the function of the surface or manufacturing process. For this purpose, recommendations for the configuration and extensions of the toolbox can also be developed, which could find their way into the ISO standards.