Prediction And Suppression Of Regenerative Chatter In External Turning Of TC4 Titanium Alloy

With the rapid development of CNC machining technology,high-strength and high-plasticity hard-to-machine materials such as titanium alloy and high-strength steel are more and more widely used in aerospace,navigation and other fields.Although titanium alloys have the advantages of high strength,low density,high temperature and corrosion resistance,flutter often occurs when turning titanium alloys in outer circle due to low thermal conductivity and high tensile strength.At present,domestic scholars have initially classified the flutter into three types through experimental research: friction type flutter,vibration coupling type flutter and regenerative type flutter,among which regenerative type flutter is generally accepted.When regenerative flutter occurs,the tool will gradually leave irregular ripples on the surface of the workpiece with harsh noise.Moreover,actual machining shows that the tool wear rate increases sharply or even damages when regenerative flutter occurs.In this thesis,the phenomenon of regenerative flutter generated in the process of turning TC4 titanium alloy with outer circle is studied.A mechanical model of regenerative flutter with tool system as the main vibration system is established.The dynamic parameters are identified experimentally and the stable lobe diagram is drawn.Cylindrical turning test is carried out according to the predicted results of stability petal pattern.The experimental analysis shows that when the point composed of back feed and speed is above the petal curve,compared with the point under the petal curve at the same speed,the average amplitude increases by about 1 times,the roughness increases by about 31%,and the turning is unstable.The experimental results verify the accuracy of the stability petal diagram and enhance the reliability of the results by means of comparative analysis.For regenerative flutter caused by TC4 titanium alloy turning in outer circle,radial vibration cutting technology is adopted to suppress the occurrence of regenerative flutter(compared with irregular flutter caused by regenerative flutter in traditional turning,the vibration on workpiece after radial ultrasonic vibration turning is smoother,more uniform distribution and more thorough material removal.It effectively reduces surface scratches and debris tumors caused by titanium chip stickers).Based on Johnson-Cook constitutive model and Zorev friction model,the finite element model of TC4 for cylindrical turning is established.Finite element simulation of TC4 for conventional cylindrical turning and TC4 for radial vibration cylindrical turning is carried out by using Third Wave Advant Edge cutting simulation software.Analysis of simulation results shows that the optimum amplitude for radial vibration cylindrical turning of TC4 titanium alloy is 10?m.According to the principle of ultrasonic vibration cutting,the radial ultrasonic vibration turning device is selected.SCQ-1500 F ultrasonic generator,sandwich piezoelectric transducer and stepped deformation amplitude bar are customized.According to the vibration frequency of 20 k Hz and the requirement of radial vibration,modal analysis and harmonic response analysis are carried out in workbench software,and the radial vibration tool bar with main deflection angle of 75 ° is designed.The structure size of the radial ultrasonic vibration system is modified,and the L-shaped plate is used to clamp the radial ultrasonic vibration system on the turret.The time-domain waveforms,surface roughness and vibration pattern of TC4 titanium alloy under different cutting parameters were analyzed by orthogonal experiment.It can be seen from time domain analysis that when using radial ultrasonic vibration cutting technology for cylindrical turning of TC4 titanium alloy,when the tool bar contacts with the workpiece,the radial ultrasonic vibration is coupled with the vibration generated along the X axis of the machine coordinate system,and the amplitude decreases rapidly;when the turning work is completed and the turning tool is separated from the workpiece,the coupling effect disappears and the amplitude returns to 10 ? m left Right.The analysis shows that the radial vibration has a good suppression effect on the regenerative flutter.According to the comparison between the traditional external turning TC4 titanium alloy and the radial vibration external turning TC4 titanium alloy,after the radial vibration external turning,the vibration marks on the surface of TC4 titanium alloy are smoother and more evenly distributed,and the material is removed more thoroughly,which effectively reduces the surface scratches and chip accretion caused by the titanium alloy chip sticking cutter.It can be seen from the relative ratio of the surface roughness curve of TC4 titanium alloy that the surface roughness of TC4 titanium alloy is obviously reduced and the surface machining quality of TC4 titanium alloy is improved after radial vibration turning.