Tool wear and cutting forces when machining inconel 718 under cryogenic conditions: Liquid nitrogen and carbon dioxide

Abstract

Nickel-based superalloys are widely exploited in turbojets components which are subjected to intense thermal and mechanical loadings during their operation. In fact, they exhibit excellent mechanical properties over a wide range of temperature and high corrosion and creep resistance. However, these materials induce several problems related to the shaping by machining due to essentially high heat resistance, high hardening tendency, high chemical affinity with tool material and low thermal conductivity leading to very high temperature in the cutting zone. In this context, assisted machining processes aim to improve the productivity of certain materials that are difficult to cut. Indeed, in order to keep the tool cold, it has been proposed to use cryogenic fluids (liquid nitrogen LN2 and carbon dioxide CO2 as coolant for effectively reducing temperatures since their vaporization temperatures are equal to -196°C and -75°C respectively. In this context, previous researches have focused on the study of the efficiency of this technique with respect to the machinability of several materials such as titanium alloys and nickel-based alloys. It has been shown that the tool life is improved when machining titanium alloys, unlike nickel-based alloys. For this reason, this paper is devoted to a comparison between two cryogenic fluids (LN2 and CO2) with regard to their effects on tool life when machining Inconel 718 considering as a reference the conventional lubrication. Results showed that tool life is the longest in conventional lubrication. However, under cryogenic conditions, tool life is the shortest in the case of LN2 condition whereas CO2 condition exhibits lower value compared to the traditional lubrication.