Influence of high-speed cutting and pre-cooled neat oil on AISI 304 gear surface integrity and geometric accuracy after hobbing

Austenitic stainless steels are attractive for gear applications that require corrosion resistance; however, their poor machinability limits hobbing productivity. This study evaluated the influence of high-speed cutting and pre-cooled neat oil on the surface integrity and geometric accuracy of AISI 304 gears. Cutting speeds of 180, 240, and 300 m/min were tested under non-cooled and cooled oil conditions using a TiAlN-coated carbide hob under controlled tool-wear conditions (VB max < 200 μm). The surface roughness, ISO 1328 profile and lead deviations, near-surface microhardness, and XRD residual stresses were evaluated. The Ra and Rz roughness values were not significantly affected by the cutting speed or oil-supply condition at the 95% confidence interval. The oil-supply condition significantly influenced the left-flank profile deviation Fα whereas the left-flank lead deviation Fβ was significantly affected by the interaction between the cutting speed and oil-supply condition. Suitable geometric responses occurred under the cooled-oil condition at 240–300 m/min cutting speed range. The microhardness values varied from 241 to 255 HB, whereas the XRD residual stress values remained highly scattered. Overall, cutting operations up to 300 m/min were feasible without significant roughness deterioration, although residual-stress variability prevented the identification of a globally optimal condition.