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The present study deals with performance investigation of cryogenically treated plus tempered carbide inserts during machining of Inconel 718. A novel cooling approach of combined minimum quantity lubrication with cryogenic coolant, cryogenic minimum quantity lubrication is examined to improve the machinability of Inconel 718 and compared with dry, wet, minimum quantity lubrication, and cryogenic cooling conditions. Tool wear, cutting forces, and chip morphology were analyzed to evaluate the effect of cooling under different conditions. The results revealed that minimum quantity lubrication and cryogenic conditions exhibited superior performance than wet and dry conditions. However, severe tool fracture and cutting forces were observed in cryogenic machining which is an outcome of hardened surface of nickel alloy due to cryogenic fluid. Cryogenic minimum quantity lubrication was understood to be the best machining condition generating least cutting force and tool wear. Furthermore, examining chip morphology under scanning electron microscopy revealed that cryogenic minimum quantity lubrication performed stable machining.

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The influence of turning parameters on the surface integrity of the workpiece in hard turning of AISI 52100 steel using minimum quantity lubrication (MQL), was investigated in this work. The cutting parameters considered were cutting speed, feed, depth of cut and tool nose radius, at three levels each. Response surface methodology was employed to study the influence of factors on surface roughness, microhardness, topography, white layer thickness and elemental composition. From model analysis, the microhardness and surface roughness were best predicted by quadratic regression models, whereas white layer thickness was best evaluated by a linear model. The variance analysis revealed that surface roughness was significantly affected by nose radius (33·83%), followed by feed (32·5%). It was observed that surface defects were reduced with an increase in cutting speed. Microhardness was majorly affected by feed (36·64%), followed by nose radius (32·88%). The white layer thickness ranged from 4·3 to 15·9 μm for all experiments. White layer thickness was significantly influenced by nose radius (82·24%), cutting speed (9·78%) and feed (1·23%). Energy-dispersive X-ray spectroscopy analysis of the machined workpiece at a cutting speed of 150 m/min validated that oxidation was instigated and the weight percent of carbon was augmented in the base metal.

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