Image-Based Monitoring of Tool Wear in Micro End Milling of Hardened Steel

Micro milling is a flexible process that allows the fabrication of micro molds using end mills with diameters typically below 0.5 mm. Mold materials are commonly selected from steels, such as AISI 420, with hardness values ranging from 55 to 65 HRC. Consequently, tool wear presents a significant challenge during micro milling operations. Monitoring tool wear can be accomplished via direct or indirect methods. In this study, a direct approach is employed to measure wear in micro end mills. Images of bottom view of the micro end mill are captured using a microscope integrated into the CNC micro milling center, enabling image acquisition without removing the micro end mill from the tool holder. Advanced image processing techniques are utilized to identify and quantify the edge radius of the end mill as the cutting tool wears out, which may serve as input for the remaining useful life (RUL) prediction algorithms. The experimental findings demonstrate the associated challenges in calculating the edge radii of micro end mills during the machining of hardened steel components.