Influence of hexagonal phase transformation in laser prepared PcBN cutting tools on tool wear in machining of Inconel 718

Abstract

Laser preparation of PcBN cutting tools is a new approach to improve the performance of different machining applications. Laser machining is robust and wear-free which offers benefits compared to conventional methods, such as grinding and brushing. Moreover, the conventional preparation methods are limited for the preparation of super hard cutting tool materials and the generation of complicated geometrical features because of high tool wear. A highly demanding application of PcBN cutting tools is the machining of Ni-based super alloys such as Inconel 718. For various high and low temperature applications in aerospace systems this material is popular because of its temperature, oxidation and corrosion resistant characteristics. However, these characteristics and an intense work hardening behavior make Inconel 718 a hard-to-cut material. A possibility to increase the performance in cutting hard-to-cut materials is the application of a process specific cutting edge rounding prepared by laser machining. However, there is no available knowledge neither on the influence of laser machining on the material properties of PcBN nor on the influence on the cutting performance. This research deals with the effect of laser preparation on the cutting performance of PcBN tools in machining Inconel 718. Different laser preparation strategies are applied to provide necessary knowledge regarding the laser preparation process. The formation of hexagonal boron nitride (hBN) on the surface is found for all of the applied laser preparation strategies, however the degree of the cBN to hBN transformation differs between the applied strategies. Within the cutting experiments the wear behavior is closely linked to the formation of hBN, which decreases the hardness of the PcBN material. Furthermore, process forces for the laser prepared tools are reduced compared to the conventional tools, which might be an influence of the hBN acting as a solid lubricant. Finally, it could be shown that the achieved tool life of laser prepared tools is at least on a par with conventionally machined tools.