High speed MQL finish-turning of Inconel 718 with different coated tools

Minimal quantity lubrication (MQL) was applied to finish-turning of a nickel-base superalloy, Inconel 718, with three different types of coated carbide tools. Three selected coatings were TiCN/Al2O3/TiN (CVD), TiN/AlN superlattice (PVD) and TiAlN (PVD). Cutting speeds were set at relatively higher values: 1 and 1.5 m/s. At a cutting speed of 1.0 m/s, TiCN/Al2O3/TiN coating in MQL cutting exhibited the best performance while TiN/AlN superlattice coating in MQL cutting exhibited the second best performance. The longest tool life was attained by TiCN/Al2O3/TiN coating in wet cutting, but the surface finish was not good. It was found that there is the optimum air pressure life in finish-turning of Inconel 718 with MQL. It was also found in an experiment using argon as a carrier gas of oil mist that the carrier gas of MQL plays an important role for cooling the cutting point. As the cutting speed was increased to 1.5 m/s, the tool lives were drastically shortened. In addition, the surface finish in MQL cutting increased because the worn tool flank surface became rough.