| Superalloys have excellent high temperature strength,oxidation resistance,corrosion resistance and fatigue properties.Among them,the most widely used is nickel base superalloy.But it is also because of the excellent properties of high-temperature alloys that milling becomes more difficult.With the help of nanofluid Minimum Quantity Lubrication(NMQL)technology,the cutting force and cutting temperature in milling can be effectively reduced.Compared with the traditional pouring cooling,NMQL technology can make the cutting fluid permeate between the workpiece and the tool after atomization.At the same time,the lubricating oil(ricinoleic acid)with polar groups as the main component compared with mineral oil with non-polar hydrocarbon chains as the main component,the oil film formed can effectively reduce the formation of abrasive particles.Therefore,it is necessary to study the mechanism of ricinoleic acid nanofluid improves the milling machinability of nickel base superalloy.In this paper,two aspects of cutting force and nanofluid cooling and lubrication in milling process are studied to explore the factors that ricinoleic acid nanofluid can improve the cooling and friction characteristics of milling process and affect the cutting force and thermal conductivity of nanofluid.Through comparative experiments,milling machining experiments were carried out on nickel-based superalloys under different lubrication conditions.The results show that under the condition of Minimum Quantity Lubrication,the cutting fluid can enter the cutting area well,play the role of cooling and lubrication,thus improving the surface quality of milling and reducing the milling force.At the same time,adding nanoparticles into the ricinoleic acid base fluid,the nano fluid can play a better role in cooling and wear reduction;in high-speed cutting,the nano fluid can still play a better role in improving the cooling and lubrication performance of milling process.Although the experimental results can well prove that ricinoleic acid nanofluids can effectively improve milling processability,milling process is a high-speed process.At the same time,under the influence of cutting fluid flow,the existing experimental methods can not conduct real-time micro analysis on the brown motion of nanoparticles,the behavior of solid-liquid conversion film and the deformation of nanoparticles,which can not fully and effectively explain the improvement Mechanism.According to the experimental results,using molecular dynamics method,based on the idea of simplification,the mechanism of improving milling performance after adding nanoparticles to the basic fluid was studied from the micro level.The thermal conductivity model of ricinoleic acid nanofluid and milling model underdiamond-nickel boundary lubrication were constructed.The relationship between the thermal conductivity,viscosity of the ricinoleic acid nanofluid,friction during cutting and different factors was obtained.The specific research results are as follows:(1)Adding copper nanoparticles to the ricinoleic acid base solution can effectively improve the thermal conductivity of the base solution.With the increase of the concentration,the thermal conductivity increases obviously;Under the action of Brownian motion,nano particles improve the thermal conductivity of nanofluids,increase the overall mobility of nanofluids,and reduce the viscosity;The thermal conductivity of nanofluids increases first and then decreases as the diameter of nanoparticles increases,while the viscosity of nanofluids decreases with the increase of nanoparticle diameter;Temperature has little effect on the thermal conductivity of the basic fluid,but it has a greater impact on the nanofluid,and the temperature increase will effectively reduce the viscosity of the nanofluid.When the thickness of oil film near the tool and nickel base alloy does not change,the viscosity of nanofluid decreases can reduce the friction and improve the lubrication effect.(2)Through the simulation of ni-based alloy milling,it is found that ricinoleic acid nanofluids not only form adsorption oil film around nanoparticles,but also form adsorption oil film on the surface of cutter and workpiece,which can protect the workpiece and improve the surface processing quality;It was also found that compared with hard nanoparticles,soft nanoparticles would have deformation during the compression process and would not destroy the adsorbed oil film,thus improving the carrying capacity of nanofluids under boundary lubrication. |
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