Comparison between cryogenic coolants effect on tool wear and surface integrity in finishing turning of Inconel 718

The most important challenges when machining difficult-to-cut alloys used in critical applications consist mainly in increasing tool life as well as improving the component surface integrity. In particular, the nickel based alloys exhibit very low thermal conductivity inducing higher cutting temperature and thereby rapid tool wear. In this context, cryogenic machining is a promising approach that enhances cooling efficiency either when using the liquid nitrogen LN2 or the carbon dioxide LCO2. According to previous works, cryogenic machining has been carried out on several work materials such as titanium alloys and nickel based alloys. Their findings figured out that longer tool life and better surface integrity were obtained when machining titanium alloys, unlike nickel based alloys. In this work, a comparative study has been carried out in order to investigate the cryogenic machining performance during turning operation of Inconel 718 with respect to tool wear behavior and surface integrity of the machined part. In fact, two cryogenic fluids were employed namely LN2 and LCO2 considering as a reference the conventional lubrication. This study illustrates that conventional lubrication and LCO2 cryogenic cooling allowed to obtain similar machining time, tool wear and surface finish. Nevertheless, LN2 cryogenic machining resulted in the lowest tool life as well as the poorest surface finish. Moreover, residual stresses have been measured beneath the machined surfaces when machining using new tools and tools with different levels of tool flank wear. It was observed that compared to conventional lubrication, both cryogenic conditions showed better results with respect to residual stress profiles along the machined surface