| Green manufacturing is the development trend of manufacturing industry nowadays.“Made in China 2025” and the “13th Five-Year Plan” put forward that sustainable manufacturing with resource-saving and environment-friendly is the theme of manufacturing industry today,and accords with the development strategy of new and old kinetic energy conversion in Shandong Province.In milling,the contact time between the tool and the workpiece is short,and intense friction between tool,workpiece and debris occurs;at the same time,a large amount of cutting heat is produced,which aggravates tool wear and causes thermal injuries to the workpiece surface.Therefore,lubrication plays an extremely important role in milling.Cutting fluid plays an important role in reducing the friction of milling tool/workpiece interface and achieving good workpiece surface quality.In traditional machining,flood lubrication is usually used.Although the cooling and lubrication effect is better,its shortcomings such as large amount of cutting fluid and serious environmental pollution do not conform to the theme of clean and low carbon machining.The emergence of nanofluid minimum quantity lubrication(NMQL)technology provides a new way of production,solving the problem of environmental pollution and the technical bottleneck of insufficient heat transfer capacity of minimum quantity lubrication(MQL),which is a green processing method.However,due to the formation of a gas barrier around the high-speed revolving milling tool,the injection of cutting fluid is difficult;at the same time,due to the different physical and chemical properties of different nanofluids,the lubrication effect is also different.Based on the above problems,theoretical modeling and simulation analysis of the gas flow field under the constraints of end-milling tool/workpiece are carried out,and the selection of base oil and nanoparticles for NMQL is systematically studied theoretically and experimentally.Specific research work as follows:(1)The machining mechanism of end-milling is studied,and the mathematical model of milling force is established.The related parameters for evaluating lubrication performance in end-milling are analyzed,including milling force,friction coefficient,specific energy,workpiece surface quality(Ra,RSm,Rmr value),and debris morphology.(2)Theoretical model of air flow field in the milling zone of end-milling tool/workpiece constrained interface is established and simulated.The law of air flow distribution in the milling zone is obtained,and the influence of air flow field on nozzle position distribution is further obtained.The influence rule of rotating speed,helical angle and diameter of the tool on the airflow field in milling are also studied.(3)The tribological characteristics of NMQL at the interface of tool/workpiece are studied.The lubrication performance of different lubrication modes(dry,flood,MQL and NMQL)in end-milling is analyzed.Based on the analysis of milling performance evaluation parameters,the rule of good friction reduction and wear resistance of NMQL in end-milling is obtained.(4)The effects of different vegetable oils physical and chemical properties(composition,molecular structure and viscosity)of tool/workpiece interface in MQL are studied.Five kinds of vegetable oils are used as MQL base oils in the experiment.The lubrication characteristics of the different vegetable oils are analyzed,and the influence rules of different base oils on the lubrication performance of end-milling zone are obtained.(5)The effects of nanoparticles molecular structure,shape and viscosity of nanofluids on the lubrication performance of tool/workpiece interface in MQL are studied.Six kinds of nanofluids are prepared with cottonseed oil as base oil.The effects of different nanoparticles on milling force,friction coefficient and workpiece surface quality are analyzed,and the nanoparticles with the best lubrication performance are obtained. |
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