High Performance Helical Milling of Hardened Aisi D2 Cold Work Die Steel

Abstract

This work investigates the feasibility of helical milling in producing high quality hoes in hardened AISI D2 cold work die steel (56 HRC). Considering the challenges faced by conventional hard drilling, helical milling emerges as an attractive alternative. The main goal is to investigate the influence of the cutting parameters on the quality of holes produced by helical milling using a ball nose cutter with indexable coated carbide inserts. A series of tests were conducted using the Taguchi methodology and analysis of variance. The following helical milling parameters were evaluated at two levels: cutting speed (v_c), axial depth of cut (a_p), feed per tooth (f_z), tool eccentricity and (e) and cutting direction (up and down milling). The influence of these parameters on the components of helical milling force and hole quality (diameter deviation, circularity, cylindricity, and roughness) was assessed. Cutting power and the morphology of generated chips were also analyzed. The findings indicated that helical milling was capable of producing holes in hardened steel with tighter tolerances (ISO IT7) compared with drilling and roughness of the hole wall as low as R_a = 1.8 µm). Moreover, up milling promoted lower force components, especially in the axial direction. Regarding hole quality, up milling resulted in lower diameter deviation. The axial depth of cut was the most influential factor on surface roughness. The morphological analysis of chips indicated that chips with a lower serrated degree (G_S) are associated with lower cutting power, while a higher serrated frequency (f) is related to better surface quality.