In the present investigation, machining performance of Ti6Al4V is studied under dry environment, pressurized air supply and distilled water based Minimum Quantity Lubrication (MQL). Machining (turning) performance is assessed in purview of cutting force (tangential component) magnitude, tool-tip temperature,width of tool flank wear progression, morphology of evolved chips and severity of vibrations at varied cutting speeds as well as cooling media. Characteristic features of spatial temperature distribution profile (at the vicinity of tool-tip) as influenced by varied cooling media are studied with the help of thermographs of the cutting zone. Mechanisms of cutting tool wear are studied as well. It is experienced that amongst three cutting environments tested, application of water-MQL is beneficial for machining of Ti6Al4V at low cutting speed. Severity of vibrations gets 50.39% reduced during machining under water-MQL than dry condition. Consequently, as compared to dry machining, water-MQL causes 79% reduced tool flank wear and 82% reduced crater wear at low cutting speed. Under water-MQL, reduced tool-tip temperature (66% reduced than dry condition) suppresses severity of tool wear. In comparison with high cutting speed, performance of water-MQL is found much better at low cutting speed. ‘Unaffected zones’ are identified at the worn-out tool rake face under water-MQL. High amplitude of vibration (maximum absolute mean value) causes low chip-segmentation ratio. On the contrary, chip reduction coefficient gets truncated with decrement in vibration amplitude. Vibration amplitude has positiveinfluence on degree of chip-curl.

Traditional dry machining of ‘difficult-to-cut’ titanium alloy Ti-6Al-4V has always been a challenging task. This is due to its lower thermal conductivity, strong work-hardening tendency, and extreme chemical reactivity. These causes adverse machining effects including premature tool failure, evolution of hugecutting temperature, machine tool chatter, and disappointing surface integrity of the machined work part. Selection of compatible tool material, appropriate tool geometric parameters, and adequate control of cutting parameters are of vital importance towards achieving satisfactory machining yield. In this context, performances of MT-CVD TiCN/Al₂O₃ bi-layered coated carbide, PVD TiN/TiCN/TiN multi-layered coated cermet, and CVD TiCN/Al₂O₃ bi-layered coated SiAlON inserts are studied during dry machining of Ti-6Al-4V within cutting speed range 50-130 m/min; at constant feed ~ 0.1 mm/rev, and depth-of-cut ~ 0.35 mm. Approximate tool-tip temperature (maximum value) attained during operation, magnitude of tangential cutting force, and width offlank wear progression are measured. Detailed study on wear morphology of worn-out inserts, chip’s micro/ macro morphology, and surface integrity of the machined product are carried out. It is experienced that cermet tool performs better than remaining two counterparts in purview of lower tool-tip temperature, reduced flank wear, and better machined surface integrity.

Due to high temperature strength (hot strength), excellent corrosion resistance and high strength-toweight ratio, Ti-6Al-4V alloy is considered as a potential candidate for extensive applications in aerospace and biomedical engineering. But, alloy's low thermal conductivity and extreme chemical affinity (towards toolsubstrate and coating materials) often cause an aggressive cutting environment with a tremendous rise in cutting zone temperature, premature tool wear, and disappointing surface integrity during conventional machining processes. In order to achieve desired machining yield without opting for any coolant, selection of proper cutting tool (based on their geometry and properties) is indeed vital. Thus, the present work examined the performance of MTCVD-TiCN-Al₂O₃-TiOCN multi-layer coated carbide and PVD TiN single layer coated compositeceramic (Al₂O₃/TiCN) tool inserts during dry machining of Ti-6Al-4V. Higher friction coefficient (of the coating system) was revealed for the ceramic tool which caused substantial temperature rise at tool-tip. On the other hand, carbide insert imparted lower cutting force (beyond ν = 80 m/min) than ceramic insert due to its better thermo-chemical stability. Coating peel-off and tool flaking were witnessed for ceramic insert due to its thermal instability at higher cutting speeds; while carbide tool was mainly affected by material adhesion,abrasion, and chip fusion (adhesion of broken chip-fragments over tool surface due to high pressure and temperature). It was experienced that induced cutting heat significantly affected chip morphology under a dry cutting environment. Up to ν = 130 m/min, ceramic tool exhibited lower flank wear than carbide tool.

In the present work, the machinability of difficult-to-cut Inconel 718 aerospace superalloy is studied under vegetable oil-based minimum quantity lubrication (MQL) in consideration with different cutting tool materials. MQL environment is produced by supplying air-oil mist in which biodegradable sunflower oil is used.In comparison with uncoated carbide tool, performances of MT-CVD multi-layered TiCN-Al₂O₃-TiOCN coated and MT-CVD double-layered TiCN-Al₂O₃ coated carbide inserts are assessed during longitudinal turning of Inconel 718. Coating materials are characterized by average thickness of individual coating layer, elemental composition and frictional coefficient. With constant feed and depth-of-cut (0.1 mm/rev and 0.25 mm respectively), quantitative responses such as tangential cutting force, tool-tip temperature and width of tool flank wearare considered as machinability assessment criteria under varied cutting speed condition (v = 60, 80, 100 and 130 m/min). Notable reduction in tool-tip temperature (25.6% and 30.4%) and reduction in cutting forces (10.6% and 22.3%) are obtained for coated tool [T1] and coated tool [T2] respectively, when compared to uncoated counterpart. Detailed analysis on tool wear modes is carried out followed by chip’s macro/micromorphology. Apart from chip’s micro-morphological parameters, morphologies of chip’s back and free surfacesand chip microhardness are studied.