In recent years, multi-axis cutting using small-diameter ball-end mills has been widely used owing to the growing complexity and precision required for machining geometries. However, determining the progression of tool wear and life based on operator experience remains challenging. This issue is attributable to the machining of special materials that can withstand use in harsh environments, thereby necessitating in-process detection of tool wear. This study investigates the effectiveness of a system that measures cutting-force fluctuation during machining by analyzing supply pressure fluctuations. An originally developed speed-controlled air-turbine spindle driven by compressed air was employed to estimate the progress of tool wear in-process. The results showed that cutting force increases linearly with supply pressure and cutting force during tool wear in small-diameter ball-end mills. A strong correlation was observed between supply pressure and all cutting-force components, regardless of cutting angle or overlap. A real-time tool-wear estimation model was developed, achieving a relative error below 0.2 during normal wear stages. These findings confirm that supply pressure can be used as a reliable indicator for tool wear, enabling accurate in-process estimation and supporting the automation of precision milling operations.
XIE et al. (Thu,) studied this question.