Wear mechanisms and cutting performance of coated carbides in milling LPBF IN718 alloy under hybrid cryogenic conditions

The present study investigates the milling of Inconel 718 (IN718) alloy fabricated using laser powder bed fusion (LPBF). Finish milling has been performed using Al-rich ternary-coated end mills under different lubri-coolant environments. An indigenously developed Cryo-MQL technology for greener manufacturing has been employed. Machinability results have been evaluated in terms of milling forces, tool wear progression, wear mechanisms, surface roughness, sub-surface damages and chip characteristics. MQL and Cryo-MQL conditions reduced milling forces by 50.6% and 47.2%, respectively. A 35-67% flank wear reduction has been obtained for the Cryo-MQL, resulting in minimal sub-surface deformation. Cryo-MQL caused the least milling-induced deformation with no transverse microcrack due to an excellent balance of cooling and lubrication actions. Micro-hardness of the machined sub-surface ranged 450-490 HV0.03 (100-400 mu m) for Cryo-MQL compared to 435-485 HV0.03 in a deeper sub-surface deformation zone (250-450 mu m) for dry milling. The synergy of lubri-coolant actions in Cryo-MQL mitigated frictional tracks, chip-side cracking and chip-edge fracture.