Synergistic impact of eco-friendly nano-lubricants on the grindability of AISI H13 tool steel: A study towards clean manufacturing

Abstract

The conventional flood i.e., mineral-based cutting fluid approach was extensively utilized on the shop floor to diminish the amount of friction and power consumption while precision grinding of “difficult-to-machine” materials like hardened AISI H13 tool steel. The excessive exposure and usage of conventional fluids lead to severe environmental threats like air and water pollution, and unfavourable impacts on operator health. Therefore, sustainable manufacturing in terms of minimum quantity lubrication (MQL) grinding is major concert in modern tooling industries including technological, economical, and environmental aspects. The objective of present study is to identify the impact of six different eco-friendly nano-lubricants i.e., castor oil (CO), soybean oil (SO), castor oil-deionized water (CO + DIW) emulsion, soybean oil-deionized water (SO + DIW) emulsion, Al2O3 nanofluids (NFs): 0.5 wt%, and Al2O3 NFs: 1 wt% on grindability and surface integrity indices, energy consumption, carbon emission, and production cost while MQL grinding of AISI H13 tool steel. The lubrication mechanism and its characteristics were studied by biodegradation rate, pH and sedimentation test, thermal conductivity, viscosity, surface tension, and wettability. The grindability indices, namely, apparent friction coefficient, surface roughness (Rɑ and Rz value), bearing area (BC) ratio, surface topography, and microchip morphology were evaluated and analyzed. The results suggest that the downfeed and Al2O3 NFs have the greatest impact on technological, economical, and environmental aspects of MQL grinding. It is found that the extensive cooling and lubricating performance of Al2O3 NFs was superior to that of biodegradable emulsion, and straight vegetable oil offered the optimal results under all lubrication evaluation tests. Also, significant improvement in grindability performance was obtained with Al2O3 NFs: 1 wt% owing to strong anti-friction lubricating tribo-film, and higher boiling heat transfer through effective rolling and mending effect. The grindability enhancement rates of apparent friction coefficient, Rɑ,Rz, and BC ratio are 28.48%, 59.66%, 50.18%, and 6.25%, respectively at 32 μm downfeed as followed by SO + DIW emulsion. Furthermore, poor ground surface quality along with spherical and sharp wear tracks on microchips was indicated with SO + DIW emulsion. According to sustainable aspects, Al2O3 NFs: 1 wt% outperformed straight vegetable oil in terms of lower energy consumption (17.06 kJ), carbon emission (00468 kgCO2), and production cost (0.255 $), which were 15.10%, 26.76%, and 13.55% lower than soybean oil. It is confirmed that Al2O3 NFs is the best substitute for the straight vegetable oil and vegetable oil-deionized water emulsion for robust sustainable manufacturing of tooling components.