Experimental Studies on Machinability Assessment of Difficult-to-Cut alloys (Inconel 718 and Ti-6Al-4V) During Traditional and Non-Traditional Machining

Abstract

In the present dissertation, aspects of machinability of ‘difficult-to-cut’ nickel, and titanium based alloys (Inconel 718, and Ti-6Al-4V, respectively) are studied through traditional as well as non-traditional machining. During traditional machining (longitudinal turning operation), extent of machinability is assessed in purview of tangential cutting force magnitude, tool-tip temperature, depth of flank wear, area of crater wear, and machined surface integrity. Dominant tool wear mechanisms along with chip’s macro/ micro morphology are studied in detail. Surface integrity of the machined work part is analyzed which includes surface roughness, white layer thickness, and micro-indentation hardness. In this work, performances of PVD multi-layered TiN/TiCN/TiN coated cermet and PVD TiAlN coated PCBN (Polycrystalline Cubic Boron Nitride) brazed tipped carbide inserts are studied in the context of dry machining of Inconel 718. Results, obtained thereof, are compared to that of conventional uncoated WC-Co tool. It is observed that cermet causes lower cutting force than carbide, and PCBN tool. On the contrary, PCBN tool-tip experiences lesser temperature than remaining two counterparts. Amongst three inserts tested, cermet insert provides superior surface quality which can be described by less-severe feed marks, lower roughness value, and tiny white layer depth. In addition, application potential of microwave post-treated WC-Co insert is examined for dry machining of Inconel 718. It is experienced that, as compared to untreated counterpart, microwave post-treated tool exhibits higher hardness, and better wear resistance which, in turn, cause lower flank wear, and reduced tool-tip temperature. During microwave treatment, favorable microstructural alteration (skeleton-type structure) followed by formation of complex carbides results in improved mechanical properties of the tool material. Additionally, this dissertation includes machinability study of Ti-6Al-4V under Nanofluid Minimum Quantity Lubrication (NFMQL) in which Multi-Walled Carbon Nano-Tubes (MWCNTs) dispersed in commercially available rice bran oil, is utilized as nanocutting fluid. It is experienced that NFMQL outperforms dry machining, and machining under conventional MQL. Under NFMQL machining, ‘unaffected zones’ are distinctly identified over worn-out tool rake face which clearly confirms sustenance of strong film of boundary lubrication for prolonged machining duration; thus, protecting tool substrate. Apart from conventional machining (turning), non-conventional routes like Electro-Discharge Machining (EDM) and Wire Electro-Discharge Machining (WEDM) are attempted to evaluate machinability of Inconel 718 as well as Ti-6Al-4V. Application of MWCNTs added kerosene (as dielectric media) is recommended for EDM of Inconel 718. As compared to conventional (dielectric media with no additives) EDM, better machining performance, in purview of higher material removal efficiency, and lesser extent of electrode wear, is obtained in case of additive-mixed EDM. Improved machined surface integrity (better surface finish, lower crack density, and lesser recast layer thickness) is achieved in additive-mixed EDM when compared to conventional EDM. Finally, the present dissertation work attempts to investigate surface integrity of machined Ti-6Al-4V specimen obtained through multi-cut strategy (one main/ rough cut followed by multiple trim/ finish cut) of WEDM. As compared to main cut, better surface integrity is attributed to WEDMed Ti-6Al-4V specimen obtained through finish cut. Formation of rutile TiO2 over WEDMed surface is detected during finish cut which is expected to improve biocompatibility of Ti-6Al-4V work material.