| Inconel718 alloy has excellent high temperature strength,high temperature oxidation resistance and corrosion resistance.It is favored by aerospace,ship,automobile and military industries.Because of its large plasticity,low thermal conductivity and a large number of hard points,burr and surface defects are easy to occur in the micromilling process.Vibration cutting has separation characteristics,impact characteristics,variable speed characteristics and reciprocating ironing characteristics,which makes it have excellent performance in cutting force,cutting temperature,stress and strain,chip formation,surface integrity and so on.Therefore,using ultrasonic vibration assisted micromilling technology to solve the problem of micromilling Incoenl718 has important research significance.In this study,Inconel718 is taken as the research object,and the cutting process is simulated by finite element method and micromilling experiment is carried out.The effects of different cutting parameters on burr formation and surface quality were studied,and the parameters were optimized.The main research contents are as follows:Firstly,based on the simulation of two-dimensional and three-dimensional cutting process and tool tip trajectory,the conditions of chip formation,chip breaking,cutting force,cutting temperature,stress-strain and burr formation are studied.The results show that when the ratio of cutting thickness to cutting edge radius is greater than 0.25,the condition of chip formation can be reached,and when the ratio of amplitude to feed per tooth is greater than 0.5,the condition of chip breaking can be reached.Compared with traditional micromilling,ultrasonic vibration assisted micromilling reduces the average cutting force and cutting temperature,expands the strain range and reduces the energy required for damage.In addition,ultrasonic vibration reduces the extrusion effect between the tool tip and the material,and is conducive to the chip breaking,thus reducing the burr size on both sides of the milling groove.Secondly,the effects of different cutting parameters on the morphology and size of chip and burr were studied by single factor micromilling experiment.The results show that,on the one hand,ultrasonic vibration assisted micromilling can improve the chip breaking ability and reduce the chip size,especially under the conditions of low speed,large amplitude and large feed.On the other hand,ultrasonic vibration assisted micromilling can produce tearing burr and flocculent burr,and effectively reduce the burr size,especially under the conditions of low speed,large amplitude and large feed.Combined with the simulation results of burr and milling experiment results,it is found that there is a close relationship between chip and burr.The experimental results also confirm the accuracy and reliability of finite element simulation.Finally,the effects of different cutting parameters on surface quality and corrosion resistance were studied by single factor micromilling experiment.The results show that there are three kinds of surface defects in the micromilling process of Inconel718 alloy:pits,humps and gullies,which are closely related to the formation of built-up edge.After the ultrasonic vibration is applied,the uniform and regular fish-scale surface is produced,which effectively improves the surface quality.Under the conditions of small speed,small feed and moderate amplitude,the improvement effect on the surface defects is the most obvious,and the larger amplitude will have a negative impact on the surface quality.In addition,through comprehensive analysis of polarization curve,impedance spectrum,equivalent circuit component estimation and surface morphology,it is concluded that the surface roughness can not completely determine the corrosion resistance.Compared with traditional micromilling,the surface corrosion resistance of ultrasonic vibration assisted micromilling is significantly improved,and the uniform and wide fish-scale surface is the most obvious. |
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