Hybrid cooling and lubricating technology for CNC milling of Inconel 718 nickel alloy

Inconel 718 is the most used nickel based super alloy. High material strength, hardness and corrosion resistance at elevated temperatures together with good creep resistance has made Inconel 718 an attractive material which is widely used in aerospace, gas turbine, marine and oil and gas industries. Due to the high material strength and work hardening tendency of Inconel 718, high temperatures and forces are produced during machining operations. Low thermal conductivity of the material prevents effective heat dissipation resulting in very high temperatures at the cutting zone. These high temperatures together with high cutting forces can lead to significantly reduced tool life and poor surface quality of machined parts. Therefore, machining Inconel is usually synonymous with poor productivity and high costs. In this paper the effect of various machining environments on machinability of solution treated and age hardened Inconel 718 in high speed milling is investigated. The investigations clearly demonstrated that high speed machining using a novel hybrid cooling system consisting of liquid nitrogen cryogenic cooling and rapeseed oil vegetable minimum quantity lubrication has major advantages in machining Inconel 718. The analysis indicated that tool life can be almost doubled using hybrid cooling when compared to conventional flood cooling whilst generating a surface roughness Ra of maximum 0.4µm.