EXPERIMENTAL INVESTIGATIONS AND MODELLING FOR SUSTAINABLE MACHINING OF DIFFICULT-TO-CUT MATERIALS USING ULTRASONICALLY ATOMIZED NANOCUTTING FLUIDS

Abstract

Nickel alloys find applications in critical conditions such as aerospace, automobile, chemical plants, petroleum, and other harsh environments due to their superior corrosion resistance, hot hardness, high toughness, and excellent fatigue strength. Due to the requirement of the near net shape of the components used in the assembly of components, machining is ubiquitous for manufacturing any product. However, nickel alloys have been termed as difficult-to-cut materials due to their poor machinability and low thermal conductivity. Machining of these alloys encounters high temperatures in the machining zone, leading to low tool life and poor surface finish. Moreover, excessive tool wear and heat accumulation at the machining zone results in thermo-mechanical stresses in the components, leading to poor surface integrity. The poor surface integrity affects the fatigue strength and useful life of the components. In order to dissipate the heat, an excessive amount of coolants has been used in the machining industries. The cost of the coolant is so high that it affects the machining economics. Moreover, the traditional lubricants and coolants used in the metalworking industries are petroleum-based emulsions that affect the environment in terms of fumes, carcinogenic emissions, soil pollution, etc. Besides this, emissions from traditional lubricants affect occupational health and safety. Therefore, in recent years research has been shifted towards developing environmentally benign manufacturing processes that cater to the three sustainability dimensions. Further, global commitments and environmental regulations have compelled industries to look for sustainable machining techniques focusing on green cutting fluids and neardry lubrication techniques. The present research work focused on the preparation of a novel cutting fluid, development of the Ultrasonically Atomized Fluid (UAF) process, which is a modification of the MQL technique, comparison of newly developed process with existing processes, development of statistical models for process and development of a sustainability assessment framework. In this regard, jatropha oil-based unitary and hybrid nanofluids have been prepared and characterized for the properties required for lubricants. Alumina (Al2O3) and Zirconia (ZrO) nanoparticles have been used to prepare nanofluids in various concentrations. The prepared nanofluids were investigated for their dispersion stability, thermal stability, rheological characterization, thermal conductivity, wettability study, and anti-corrosion properties. It has been found that prepared nanofluids have the properties required for lubricants. Further, the LCA of prepared nanofluids shows that they have a negligible adverse effect on the environment and are far superior to conventional lubricants. A new modified lubrication process named UAF has been developed, which used ultrasonic vibrations to atomize the cutting fluid into micro droplets of uniform size that can produce efficient lubrication and cooling. The process is a modification of the MQL technique where mist particles are non-uniform in size and often do not provide sufficient cooling. The UAF process consumes little amount of lubricant and is termed to be a near-dry lubrication process. Nickel-based Hastelloy C-276 has been taken as the workpiece for its critical applications and poor machinability. A comparative appraisal has been made for turning Hastelloy C-276 under different machining conditions. The developed process UAF shows better performance in terms of low cutting forces, good surface finish, and low tool wear. Further, the surface integrity study reveals that machining-induced changes in the work surface have been affected minimally in the UAF process in comparison to its counterparts. The machining performance of developed unitary and hybrid nanofluids have been compared, and hybrid nanofluid has shown better machining performance. This proves that the hybrid nanofluid assisted with the UAF process has been an exemplary machining process for Hastelloy C-276. Statistical models for cutting force, surface roughness, and temperature have been developed for Hybrid Nanofluid Ultrasonically Atomized Fluid (HNUAF) process. The experiments have been designed using Response Surface Methodology (RSM). The effect of input parameters has been investigated on output responses using Analysis of Variance (ANOVA). The application of machine learning-based evolutionary algorithms for training the data and multi-objective optimization have also been considered. The influence of individual parameters on process outcomes and response surface plots for significant interactions have also been discussed. The statistical models have also been validated using experimental analysis. The machined specimen has been analyzed for the type of lubrication mechanisms produced by nanofluids.