Hybrid cryogenic/MQL helical milling for hole-making of Inconel 718

Aero-engine components are subjected to extreme service conditions, requiring high-quality holes, extended tool life, and sustainable operations during machining. This study investigates the helical milling of Inconel 718 using a hybrid cryogenic and minimal quantity lubrication (MQL) lubri-cooling strategy. The performance of this method is compared to conventional flood coolant and MQL strategies in terms of tool life, cutting forces, hole quality, and wear mechanisms. The cryogenic/MQL lubri-cooling approach achieved the longest tool life, followed by flood coolant and MQL, producing 20% more holes than in the coolant case and 71.43% more holes than in the MQL case. Roughness results obtained in the last hole machined under the cryo-MQL environment outperformed those of the last hole machined under the coolant and MQL environments by 12.76% and 16%, respectively. However, the cryogenic/MQL strategy exhibited the highest cutting forces, possibly due to material embrittlement caused by the low-temperature environment. The MQL strategy resulted in the shortest tool life, attributed to severe chip adhesion caused by the low lubrication flow rate. Adhesion was identified as the primary wear mechanism, with additional evidence of abrasion, and built-up edges. Nonparametric Friedman rank-sum and Wilcoxon tests revealed statistically significant differences among all lubri-cooling conditions for the first seven holes. The cryogenic/MQL strategy demonstrated the lowest wear, followed by flood coolant and MQL.