Optimization of tool selection and milling parameters for enhanced machinability of hardened AISI D2 steel

Abstract Milling hardened AISI D2 tool steel (60 HRC), characterized by its high hardness, toughness and wear resistance, presents significant challenges in achieving desired surface quality, minimizing burr formation and tool wear, and ensuring dimensional accuracy in medical mold machining. This research aims to identify optimal milling parameters that minimize surface roughness, tool wear, and burr formation. CBN and ceramic-coated carbide milling tools, varying in tool diameter, flute number, corner and cutting-edge radii, were evaluated under various cutting conditions. Empirical power-law models were developed to predict surface roughness (Sa) and average burr height (H B-avg ), revealing that feed per tooth, cutting speed, tool diameter, axial depth of cut, and corner radius significantly influence Sa, while H B-avg was primarily governed by milling strategy, feed rate, and radial depth of cut. A radar-based multi-criteria decision-making framework was employed to select optimal tools. Subsequent experiments investigated the influence of cutting speed, feed per tooth, and milling strategy on cutting forces, surface roughness, average burr height, and microhardness. Results showed that ceramic-coated carbide tools outperformed CBN tools in roughing and finishing by providing higher material removal rates, lower tool wear and cost, and acceptable surface finish, although CBN tools yielded lower average burr height. Up milling reduced H B-avg by up to 76.8%, while increased feed per tooth deteriorated surface roughness by ~12%. Additionally, trochoidal milling produced more stable tool engagement than side milling during roughing. Optimal surface roughness was achieved under low feed per tooth and moderate cutting speed, while up milling significantly reduced burr formation. Graphical Abstract