Effect of Cooling Conditions on the Cutting Performance in High-Speed Turning of Hardened D6AC High-strength Steel Using PCBN Tools

High-speed precision cutting of hardened high-strength steel is a pivotal strategy for streamlining process chains, enhancing cutting efficiency, and reducing manufacturing costs. To examine the influence of cooling conditions, high-speed turning experiments were conducted on hardened D6AC high-strength steel with polycrystalline cubic boron nitride (PCBN) tools under both dry and wet cutting environments. A comparative analysis was carried out on tool wear, cutting temperature, cutting forces, chip morphology, and surface roughness. Dry cutting resulted in better tool wear resistance, as evidenced by a 25% increase in tool life to reach the flank wear limit ( VB _max = 300 µm) compared to wet cutting. The predominant wear mechanisms were characterized by crater formation on the rake face and grooving on the flank face under both dry and wet cutting, in addition to which the tool produced tiny edge chipping under wet cutting. The workpiece temperature was significantly lower than the chip temperature in dry cutting. The influence of cooling conditions on the cutting forces was minor; the force components were initially in the order F _z > F _y > F _x , which later changed to F _y > F _z > F _x as cutting proceeded. Chips produced under wet cutting conditions were consistently serrated; although dry cutting initially produced similar serrated chips, the serration morphologies became less pronounced as the cut progressed. Wet cutting produced lower values of surface roughness.