Sustainable development and green manufacturing are becoming an international consensus in the face of the threat of severe environmental pollution and waste of resources. Cryogenic air (CA) and nanofluid minimum quantity lubrication (NMQL) are state-of-the-art green manufacturing technologies. However, the lubricating performance of cryogenic air is ineffective, and the cooling ability of nanofluids minimum quantity lubrication is unsatisfactory. To specifically address the bottlenecks in these manufacturing methods, a new green processing technology combining their advantages was proposed, namely, cryogenic air nanofluid minimum quantity lubrication (CNMQL). Compared to traditional processing modes and other green technologies, cryogenic air nanofluid minimum quantity lubrication is superior for its economic efficiency, low carbon use, high utilization efficiency, energy saving as well as excellent cooling and lubricating performances. A surface grinding experiment was conducted under three lubricating conditions (cryogenic air, minimum quantity lubrication, and cryogenic air nanofluids minimum quantity lubrication) with Ti6Al4V as the workpiece material. Experimental results showed that: cryogenic air nanofluids minimum quantity lubrication achieved the best lubricating effect and obtained minimum specific grinding energy (51.96 J/mm3) and friction coefficient (0.60), followed by nanofluids minimum quantity lubrication and cryogenic air. The lubricating mechanisms under cryogenic air nanofluids minimum quantity lubrication and nanofluids minimum quantity lubrication conditions were also analyzed according to the viscosity of nanofluid lubricants in grinding zone, contact angle, stability of lubricating oil film, atomization effect of droplets, and microtopography of workpiece surface. Relative to other conditions, the higher viscosity and larger contact angle of nanofluid lubricants under cryogenic air nanofluids minimum quantity lubrication condition led to higher stability and better lubricating effect of the lubricating oil film in the grinding zone. Droplets sprayed onto the grinding zone had a larger atomization angle, and the distribution density of droplets in the entire atomization spraying zone was relatively uniform. The droplets were uniformly distributed and had a larger spreading area, facilitating superior atomization effect in the grinding zone. On the other hand, workpiece surface had clear and smooth grinding pipelines, which presented minimal obstruction for the longitudinal flow and horizontal spreading effect of the micrometer pipelines, so the nanofluid lubricants achieved better spreading infiltration effect. Under the joint influence of the above factors, cryogenic air nanofluids minimum quantity lubrication achieved optimal lubricating effect, thus obtaining minimum specific grinding energy and friction coefficient.

Experimental assessment of an environmentally friendly grinding process using nanofluid minimum quantity lubrication with cryogenic air