Research On Nanofluids-based Minimum Quantity Lubrication Technology During Tapping Process Of Cast Aluminum Alloy

Oil-based cutting fluids is the heart of metal cutting process.Traditional oil-based cutting fluid composed of mineral oil with a certain percentage of chemical additives.However,the non-degradability of mineral oil and the carcinogenicity of chemical additives has posed a great hazard to the workers' health problems and the ecological environment,too.For the purpose of saving energy and protecting the environment,the development of the green cutting technology with new efficient oil-based cutting fluid as the core has drawn more and more attention.To troubleshoot the problems above,first of all,green vegetable oils instead of mineral oil were used as cutting fluids base oil in this paper,the graphene nanosheets were used as extreme pressure additive,which were used to prepare nano-cutting fluids through ultrasonic dispersion.Then,a minimum quantity lubrication(MQL)system was developed as the liquid supply device for nano-cutting fluids,and its three dimensional spray transient flow field was simulated.Finally,a tapping torque test bench was set up to systematically test the application of nano-cutting fluids MQL technology in tapping process.Research results showed that:(1)Tapping torque obtained with nanofluids-MQL technique was significantly lower than that of vegetable oils-MQL technique.0.5-wt% of GNS in base oil was the best concentration of nano-fluids in term of load-reduction.At this concentration,the average torque obtained with castor oil-based,rapeseed oil-based and corn oil-based nanofluids-MQL technique was 11.4%,16.4% and 17.7% lower than that of pure vegetable oils-MQL techniques,respectively.(2)Among three lubricating methods: pure vegetable oils-MQL,nanofluids-MQL and emulsion pouring lubricating method,the surface finish of thread obtained by emulsion pouring lubricating method was the highest,followed by nanofluids-MQL technique,and the vegetable oil MQL techqiue was the lowest.The advantage of nanofluids-MQL technique was to suppress the surface defects of the thread.(3)The application of nanofluids-MQL technique has its advantages compared to the traditional emulsion pouring method at high cutting speeds.At the cutting speed of 20 m/min,the average torque obtained with 0.5-wt% castor oil-based,rapeseed oil-based and corn oil-based nanofluids-MQL technique was reduced by 3.31%,3.89% and 5.84% compared to that of emulsion pouring method,respectively.(4)According to physical and chemical properties test results,the kinematic viscosity of nanofluids were higher than that of pure vegetable oils.Meanwhile,the stable contact angle of nanofluids droplet on the surface of alloy steel was also lower than pure vegetable oil,it suggests that nanofluids have better loading capacity and wetting ability than vegetable oils.The use of nanofluids-MQL technique can greatly reduce the amount of cutting fluids,while reducing cutting load and improve the surface quality of the workpiece.As an alternative to conventional mineral oil-based cutting fluid pouring method,its development and application has a very broad development prospects.