Performance Assessment and Optimization of Bio-Modified SiO2 Nanofluid Assisted CNC Turning of Mild Steel utilizing Taguchi based GRA/TOPSIS

Abstract

The development of environmentally sustainable and performance-enhancing cutting fluids is increasingly vital in modern machining industries. This study experimentally investigates the performance of bio-modified nanofluid composed of nano-silica dispersed in sunflower oil with aloe vera extract as a base fluid. The study also aims to optimize CNC turning process parameters using Taguchi-based multi-response optimization methods. The performance of the developed nanofluid was compared to conventional water miscible cutting fluid during the machining of mild steel under minimum quantity lubrication (MQL) condition. The synthesized fluid at 0.25, 0.5, and 1 wt.% concentration of nano silica was characterized for viscosity, density, pH, and stability. Matrix of experimental trials was formed using an L9 Taguchi orthogonal array, and analysis of variance (ANOVA) and regression models were conducted. Two multi-response optimization methods were utilized, namely gray relational analysis (GRA) and technique for order preference by similarity to the ideal solution (TOPSIS). Surface roughness (R), material removal rate (MRR), and cutting temperature (CT) were measured as key machining performance indicators. Among the prepared nanofluids, the fluid containing 1 wt.% Nano silica showed the maximum viscosity at different temperatures, the highest density, the lowest stability, and a near-neutral pH. The experimental result showed that Surface Roughness reduction average of 10.28%, MRR increased by an average of 7.2%, and CT was 7.6% lower compared to the conventional. Such enhancements are attributed to the synergistic effects of nano silica and the base fluids thermal dissipation and lubricating characteristics. Both optimization methods identified 91 m/min cutting speed, 0.125 mm/rev feed, and 1 wt.% concentration of nano silica as optimal CNC turning parameters of mild steel. The findings demonstrate the potential of the proposed bio-modified nanofluid as an effective, eco-friendly alternative for sustainable and precision machining application.