Precise measurement of worn-out tool diameter using cutting edge features during progressive wear analysis in micro-milling

Abstract Increase in edge radius, decrease in diameter, and growth of flank wear are three commonly used indices for quantitative assessment of the micro-milling tool wear. Worn-out tool diameter is usually measured by observing it under a microscope at low magnification, and this leads to significant measurement error (up to 20% of the tool life). When edge geometry changes with progressive wear, the outer diameter also decreases synchronously. In this article, a correlation between the changes in edge features and the corresponding reduction in outer diameter is developed to calculate the latter more precisely. For this purpose, first, analytical expressions are derived for different wear scenarios (uniform abrasion, non-uniform abrasion, adhesion, and edge-chipping). Validation of these expressions is further carried out through sustainable minimum quantity lubrication (MQL) assisted micro-milling of Ti–6Al–4V using TiAlN-coated WC/6Co micro-mills. Various stages of tool wear are characterized, and suitable parameters for quantifying the same are assessed. While the directly measured diameter values are affected by inconsistency and negative wear rate, the corresponding estimated values vary consistently and reliably with positive wear rate across different regimes. The diameter reduction is further established as the preferred variable for drawing tool life curve in micro-milling.