PVD multi-coated carbide milling inserts performance: Comparison between cryogenic and dry cutting conditions

This study experimentally investigates the influence of cryogenic CO2 and dry cutting conditions on the performance of multi-coated PVD tungsten carbide ball nose inserts during high-speed milling of Inconel 718. The areas of focus were the tool life, surface roughness and wear mechanisms. For the cryogenic CO2, a new cooling method approach was applied for a consistent cooling flow deep into the cutting point. The results revealed that the inserts under cryogenic conditions outperformed those under dry cutting where it was possible to improve tool life and surface roughness by an average of 75% and 142.8% respectively. It was also evident that the multicoated tools experienced a hardening effect under cryogenic cutting which increased its hardness as well as its wear resistance. Both cutting conditions showed similar tool failure modes which were dominated by notching and build-up-edge (BUE) on the flank face, as well as flaking on the rake face. However, dry cutting generated severe BUE which accelerated the notching and flaking, as well as the wear rate and caused the inserts to reach the end-of-life in a shorter time. The EDAX element mapping and SEM analysis on the worn inserts proved that adhesion, abrasion and coating delamination were the tool wear mechanisms under both conditions. Yet, the EDAX spectrum detected the presence of the oxygen (O) element which confirmed that the inserts experienced oxidation wear during the dry cutting process and caused them to weaken prematurely. The findings could provide other insights into different approaches of cryogenic cooling applications and their impact in high-speed cutting.