Deburring of micro-milled hardened steel: influence of milling strategies and CNC-based post-polishing

Abstract Hardened steels are extensively used in the automotive, aerospace, and medical industries due to their hardness and wear resistance and simultaneously high toughness. However, these properties present significant challenges in micro-milling, leading to rapid tool wear, poor surface quality, and substantial burr formation. Refining machining parameters, including cutting speed, feed rate, and milling strategies, is essential to enhance part quality and reduce post-processing efforts. This study first investigates machining parameters to minimize surface roughness and burr formation in micro milling of 60 HRC hardened steel, followed by the development of a CNC deburring method for the complete removal of burrs from edges. Experiments incorporated trochoidal micro milling for slot creation and roughing, followed by a detailed evaluation of cutting speed, feed per tooth, and milling strategies (down-milling vs. up-milling) during micro finishing. The results indicate that micro down milling at an optimal cutting speed of 80 m/min and a feed per tooth of 6 μm achieved the best surface quality (Sa = 0.85 μm), which is approximately 50% lower than the surface roughness obtained from the initial trochoidal milling- while also minimizing burr formation. To further refine the process, a polyurethane-bonded SiC polishing tool was employed in the same CNC center immediately after micro milling, completing the deburring process via top micro polishing. This optimized approach enhances production efficiency and sustainability in machining hardened steel, offering a viable solution for high-precision applications.