| Green manufacturing is an important part of advanced manufacturing technology.As the key technology of Energy Conservation & Emission Reduction,Minimum Quantity Lubrication(MQL)has the advantages of less energy consumption,green and low cost.It is the main development direction of advanced machining technology,and has attracted great attention of mechanical engineering experts and scholars at home and abroad.In this study,theoretical analysis,numerical calculation and experimental verification were used to carry out the systematic theoretical and experimental research on the injection direction of oil droplets,transportation path and form,permeability and adsorption characteristics,lubrication and action mechanism of nanofluids in MQL machining.The main contents and works are as follows:1)Based on MQL machining test,the optimum injection direction of MQL was obtained,and the cutting negative gradient pressure zone was found.Through the turning experiment,the phenomenon of negative gradient pressure in cutting process was found.Through the theoretical analysis of boundary layer and CFD simulation calculation,the distribution of pressure and velocity in turning wedges were obtained,and the formation mechanism of negative gradient pressure zone in MQLmachining was revealed.The experimental results shew that the best injection direction was to the the major flank compared with the rake face and the minor flank.2)Based on fluid atomization theory,the dynamics and kinematics models of MQL oil droplet were established.MQL device structure was analyzed,and the PDA test was conducted.The atomization distribution influences of oil,oil amount,air flow rate and intercept on the size,speed and number of oil droplet were obtained.3)The physical model and mathematical model of interfacial dendritic capillary infiltration and adsorption were established,and the processs of atomization infiltration and gas phase infiltration was revealed.The experimental device for measuring the permeability of cutting fluid wasw developed to measure the permeability of cutting fluid,and the experiment of permeable oil was carried out.The effects and variation of torque,roughness,injection time,air flow rate,oil quantity,intercept and oil products on the permeable oil quantity were revealed.4)Based on the adsorption theory and boundary lubrication theory,the gaseous adsorption velocity model and the gaseous multimolecular layer adsorption model were established.The biodegradability,oxidation stability and placement stability of trimethylolpropane trioleate,vegetable oil 6000 and polyethylene glycol 400 were measured.The contact angle and equilibrium time were measured,and the surface tension was calculated.The cutting experiments were compared and verified,and the effect of oil characteristics on the MQL properties was revealed.5)The effect of mixed nano-additives and graphene layer on MQL machining was studied.MQL orthogonal cutting experiments were conducted with different contents of nano-graphene,nano-copper powder,oleic acid and glycerol trioleate(base oil).The effects and changes of different nanoparticles and their contents on cutting force,cutting temperature,tool wear and surface roughness were revealed.A single factor experiment was carried out with a better proportion of nanofluids.The effects of multi-layer,low-layer and monolayer graphene,as well as TiAlN coating and TiN coating on MQL were revealed.6)The correlation between cutting force and surface roughness,workpiece surface hardness,and chip deformation was analyzed.The optimal variable edge distribution function and Copula function were fitted by AIC criterion and Maximum Likelihood method.Kendall rank correlation coefficient was used to quantitatively evaluate and discuss the correlation,and the hypothesis test was carried out.The study was funded by the "Study on the Formation Mechanism and Control Technology of the Burrs in the Micro-machining" of National Natural Science Foundation of China(No.51075192)and the national major special "Method for monitoring and evaluating high-speed numerical control cutting process"(No.2013ZX04009031-008).The experimental device for detecting the penetration amount of the cutting fluid,the phenomenon of the negative gradient pressure zone of the cutting process and the forming mechanism,the oil drop spray atomization characteristic and the penetration lubrication mechanism,the correlation analysis of cutting parameters were disclosed.It will further enrich and develop the MQL machining theory and the metal cutting theory,and provide the theoretical and experimental basis for the enterprise to realize the green intelligent processing. |
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