Abstract:
Hardened steels are widely used in high-stress industrial applications but face significant challenges related to heat and friction, which accelerate tool wear and reduce machining efficiency. Conventional cutting fluids, predominantly mineral-based, pose environmental and health risks. To address these issues, vegetable oils are explored as eco-friendly alternatives with superior lubrication properties. Incorporating nanoparticles into vegetable oils further enhances their thermal conductivity, lubrication, and heat transfer characteristics. However, CuO/olive oil-based nanofluid remains unexplored in machining despite its potential for improved machinability. Previous studies lack systematic approaches to optimizing stable nanofluid preparation, and the correlation between nanofluid properties and machining performance is yet to be investigated.
This study focuses on developing and evaluating stable CuO/olive oil-based nanofluids for enhanced performance in turning SKD 11 hardened steel using a Minimum Quantity Lubrication (MQL) system. CuO nanoparticles were synthesized using the co-precipitation method, and stable nanofluids with varying concentrations were developed through optimized ultrasonication parameters (60% intensity, 30 minutes). Comprehensive measurements, including thermal conductivity, viscosity, and contact angle, revealed that adding CuO nanoparticles improved the nanofluid's thermophysical properties, wettability, and lubrication performance. The nanofluids were applied using an MQL system to assess their impact on cutting temperature, material removal rate (MRR), cutting ratio, and chip morphology. Results showed that the nanofluid improved heat dissipation, reduced tool wear, and enhanced chip formation. The optimal cutting parameters were determined to be a feed rate of 0.137 mm/rev, a cutting speed of 134 m/min, and an MQL with 1 wt. % CuO nanofluid. The Grey Relational Analysis (GRA) method, applied for optimizing cutting parameters, proved reliable, achieving an absolute percentage error of only 1.097%. Additionally, correlation analysis indicated that properties such as kinematic viscosity, thermal conductivity, and contact angle significantly influenced machining performance. SEM and EDX results showed that cooling and lubrication significantly influence the wear of TiAlN-coated carbide inserts. MQL with CuO/olive oil-based nanofluid provides excellent wear resistance, with higher CuO concentrations improving tool performance by reducing friction and forming protective layers, minimizing material transfer from the workpiece. These findings underscore the effectiveness of CuO nanoparticles as solid lubricants in reducing tool wear.
This study provides valuable insights into the relationship between nanofluid properties and machining outcomes, offering a sustainable alternative to conventional fluids while enhancing machinability. These findings pave the way for future research on nanofluids in machining processes and further optimization of cutting parameters for industrial applications.