Novel application of ultra-soft and lubricious materials for cutting tool protection and enhancement of machining induced surface integrity of Inconel 718

Inconel 718 is widely used in different industries including aerospace where part quality concerns drive manufacturing process developments. However, despite extensive research, machining of Inconel 718 is still very challenging, often triggering severe surface quality problems. High temperatures and pressures generated at the contact zone during machining of this class of materials as well as high tool wear rates and aggressive built-up edge formation, result in severe work-hardening and the generation of high levels of unfavorable residual stress on the surface of the workpiece material. The current approach to overcome the high work-hardening of the workpiece and avoid wear and chipping is employing super hard tooling. However, the current results showed that, contrary to what is believed, depositing a very soft metallic layer on the tools can significantly reduce the severity of the dominant tool wear mechanism in this case and thereby improve surface quality. The results were attributed to alleviating the machining induced work-hardening of the workpiece material, which is the main root cause of its high tool wear rate and propensity to the tool chipping. Different soft and lubricous materials were deposited on the tools used for machining of Inconel 718, through an innovative technique and using conventional PVD coating methods. An in-depth surface integrity analysis is performed to study their effect on improving the integrity of the machined workpiece surface including reducing the work-hardening and residual stresses and enhancing the surface roughness.