| With the development of industrial technology,6061 Al and other light metal materials are widely used in automobile,construction,aerospace and other industries,the processing quality and precision requirements are increasingly high.Because aluminum alloy has adhesion characteristics,the traditional turning in the process of its high cutting temperature,easy to form built-up edge,cannot meet the requirements of processing quality,production efficiency is greatly reduced.As a special machining method,ultrasonic vibration turning has a good effect on improving the machining surface quality and reducing the cutting temperature.Therefore,based on ultrasonic vibration assisted turning technology,this thesis carried out researches on machining mechanism,numerical simulation,cutting test and parameter optimization of axial ultrasonic vibration turning.The main contents are as follows:Firstly,the tool path model of axial ultrasonic vibration turning was established in this thesis,and the mechanism of axial ultrasonic vibration turning was analyzed by the tool tip motion path.The results show that: when f < 2A,that is,the feed is less than twice the ultrasonic amplitude and the phase difference is φ ≥ π f / 2A,the axial ultrasonic vibration turning is interrupted cutting,and when f ≥ 2A,it is continuous cutting.In addition,the mathematical model of axial ultrasonic vibration tool bar was established.Through the workbench,the modal analysis and harmonic response analysis of the turning tool were carried out,and the axial ultrasonic vibration turning tool was designed.Secondly,two dimensional finite element models of traditional turning and axial ultrasonic vibration turning were established.Based on J-C constitutive model,sliding Coulomb friction model and arbitrary Lagrange and Euler adaptive mesh,cylindrical turning simulation experiments of traditional turning and axial ultrasonic vibration turning were carried out by using Advant Edge software.The simulation results show that,compared with conventional turning,the non-separated axial ultrasonic vibration turning performance of 6061 Al is the best when the amplitude is 10 μm,and the cutting temperature,average main cutting force and cutting stress are reduced by 6%,20.1% and 36.5%,respectively.The average main cutting force and cutting stress are reduced by 15.52% and 45.9%,respectively.Therefore,10 μm is selected as the optimal amplitude for axial ultrasonic turning of 6061 Al.In addition,the experimental platform of conventional turning,separated and nonseparated axial ultrasonic vibration turning of 6061 Al was built.The full-factor turning tests based on cutting parameters were carried out respectively,and the surface roughness of workpiece under different turning methods was obtained,and the comparative analysis was carried out.The experimental results show that the average surface roughness of axial ultrasonic turning is reduced by 12.7% and 17.7%,respectively,compared with conventional turning.There is no obvious interaction between the cutting parameters of the separated axial ultrasonic vibration cutting.The influence degree of cutting parameters on the surface roughness is as follows: feed rate > cutting speed > back engagement of cutting edge.The surface roughness of axial ultrasonic vibration turning without separation increases with the increase of back engagement of cutting edge and feed rate.However,with the increase of feed rate,the advantage of non-separated axial ultrasonic vibration turning decreases gradually.This shows that compared with the separate axial ultrasonic vibration,although the selection of the feed of the non-separated axial ultrasonic vibration can be more than twice the amplitude,it should not be too high.In addition,the time domain waveforms of conventional turning and unseparated axial ultrasonic vibration turning were collected by DHDAS dynamic signal acquisition and analysis system.As can be seen from the time-domain waveform diagram,the time-domain waveform of ordinary turning changes more violently,and the vibration of the lathe or the workpiece itself in the process of turning will produce a larger instantaneous impact force.The change of ultrasonic vibration turning is more stable,which is beneficial to restrain the chatter of turning and improve the surface quality of workpiece.Besides,the prediction models of surface roughness of turning by separated axial ultrasonic vibration and non-separated axial ultrasonic vibration were established by multiple regression method and exponential function method.The results show that the average relative error of the surface roughness model established by the exponential function method is 4.57%,and the prediction accuracy reaches 95.43%.Compared with the multiple regression model,the prediction accuracy is improved by 2.91%.The average relative error of the surface roughness model established by the exponential function method is 6.27%,and the prediction accuracy reaches 93.78%,which is 12.01% higher than that of the multiple regression model.Finally,the cutting parameters under two turning conditions were optimized by Pareto sequencing multi-objective genetic algorithm.The results show that the distribution of Pareto optimal solutions of the first front end obtained by the two optimization models is relatively uniform,and the optimization situation is good.Compared with the actual turning test,the average metal removal rate in Pareto optimal solution of separated and non-separated axial ultrasonic vibration turning is increased by 10.89% and 39.52% respectively,and the average surface roughness is reduced by 12.12% and 15.62% respectively,and the Pareto solution sets obtained under the two turning modes can provide different processing parameters.In addition to ensuring better surface quality,the processing efficiency is improved to a certain extent. |
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