Tool life estimation in micro-milling through cumulative wear modeling using direct and indirect methods

Tool wear prediction is a critical issue in micro-milling since it has a direct effect on productivity, costs, and the quality of the surface. At the microscale, tool dimensions below one millimeter result in a challenge related to the monitoring of the wear, and indirect methods of measurement are considerable topics of research. The literature underscores also a significant reliance of wear evolution on cutting parameters, especially cutting speed; however, current ISO standards provide guidelines only for constant cutting conditions. Consequently, a reliable estimation of tool life under realistic variable speed cycles remains an open challenge in micro-machining. This study addresses this gap by testing the tool life of 0.8 mm micro-end mills at a wide range of cutting speeds and collecting cutting force data. Standard wear curves obtained at constant cutting speeds are combined to construct theoretical cumulative wear curves, following a methodology recently validated in conventional size turning. Dedicated micro-milling tests are then carried out by alternating cutting speeds, enabling a direct comparison between predicted and experimental cumulative wear. Cutting forces are measured and correlated to wear in constant cutting speed and variable cutting speed tests both. The objective is to investigate whether cumulative wear behavior can still be assumed linear —as observed in conventional size machining— also at the microscale or whether nonlinear effects become significant and must be accounted for in predictive models. The proposed approach provides new insights into the mechanisms of cumulative wear in micro-tools.