Plasma Assisted Milling of Heat-Resistant Superalloys

Abstract

The term Thermal Enhanced Machining refers to a conventional cutting process in which an external energy source is used to enhance the chip-generation mechanism. The work presented here analyzes the basic aspects and the experimental results obtained when applying an assisting plasma jet to the milling process. This process, known as PAM (Plasma Assisted Milling) has been applied to the machining of three very low machinability materials: a Ni-base alloy (Inconel 718), a Co-base alloy (Haynes 25), (both belonging to the group of the heat-resistant alloys) and the Ti-base alloy Ti6Al4V. The study focuses on two major topics. First, the efficiency of the milling operation in terms of cutting speed, feed, axial and radial depths of cut and the plasma operating parameters has been addressed. Second, a study on the alterations of the metallurgical structure and the properties of materials after the PAM has also been performed. The process conditions for the above-mentioned Ni-base and Co-base alloys are detailed. The study under these conditions has shown an excellent performance of the whisker reinforced ceramic tools. In fact, cutting speeds as high as 970 m/min and large radial and axial depths of cuts are possible, driving to a cost-effective machining process. The absence of changes in the metallurgical structure of the alloys after applying the PAM process is also addressed. Therefore, it can be stated that this is a feasible approach to the optimization of the machining process of heat-resistant alloys. Finally, the results obtained in the PAM of Ti6Al4V are detailed. In this experimentation, a certain level of degradation was observed in the microstructure of the alloy when undergoing the PAM process, therefore the use of this technique is not recommended for this material.