Through-tool high-pressure coolant in production-representative internal boring: effects on tool wear, cutting power and chip evacuation

Abstract This study evaluates the effect of through-tool high-pressure coolant (HPC) on internal boring of ST52-3 steel under production-representative industrial conditions, focusing on tool wear, cutting power, surface finish, and chip evacuation. Conventional flood cooling at 20 bar was compared with through-tool HPC at 25, 40, and 50 bar in an industrial machining line. Cutting speed and depth of cut were kept constant ( v c = 220 m/min, a p = 3 mm), while the feed was increased in the HPC trials (from 0.194 to 0.265 mm/rev) to assess whether HPC could sustain more severe and potentially more productive conditions. The results showed that HPC significantly delayed flank-wear progression: the VB growth rate decreased from 0.01220 mm·part⁻¹ under conventional cooling to 0.00486, 0.00405, and 0.00311 mm·part⁻¹ at 25, 40, and 50 bar, respectively, revealing diminishing returns beyond about 40 bar. Extended tests further showed that the 40 bar condition maintained consistently lower wear up to 65 machined parts. In addition, HPC at 40 and 50 bar reduced cutting power, while 40 bar provided the most consistent chip fragmentation and evacuation. Surface roughness met the component specification after run-in for all HPC conditions, and the 40 bar condition satisfied the requirement from the first checkpoint. Overall, the study shows that through-tool HPC can improve the robustness of industrial internal boring under more demanding cutting conditions, with ~ 40 bar providing the best overall balance between tool-life extension, energetic stability, surface-finish compliance, and chip control.