Fundamental Research On Ultrasonic Elliptical Vibration Assisted Ultra-precision Cutting Of Titanium Alloy

Titanium alloy is widely used in national defense and civil industries due to their remarkable comprehensive capabilities.However,in the ultra-precision processing of titanium alloy,there are serious plastic lateral flow and elastic recovery,easy to appear the phenomenon of tool adhesion,severe tool wear,and difficulty in achieving high-quality machining,which greatly restricts the further development of titanium alloy.Ultrasonic elliptical vibration assisted cutting(UEVC)has the advantages of low cutting force,low cutting temperature,long tool life and improved machining quality.Therefore,the objective of this thesis is to introduce the UEVC technology into ultra-precision cutting of titanium alloy,and develop ultrasonic elliptic vibration assisted ultra-precision cutting process of titanium alloy.The UEVC device is an important foundation for realizing ultrasonic elliptical vibration assisted ultra-precision cutting.Therefore,a new UEVC device with sandwiched and symmetrical structure is proposed.It works with the 3rd resonant mode of longitudinal vibration and the 6th resonant mode of bending vibration,and the vibration nodes are completely superposed at the center of the flange.Therefore,the flange center is set as the only fixed point of the device,which is practical and has no interference to the resonance mode of the UEVC device.The parameters of the UEVC device are in majorization via adopting finite element methed,and the longitudinal and bending resonance modes of the device are in degeneracy.The impedance test and vibration output test of the device prototype have been carried out.It is presented by the research that the 3rd resonant mode of longitudinal vibration and the 6th resonant mode of bending vibration of the device are able to be motivated simultaneously,and the elliptical vibration trajectory is obtained.The cutting property of the device is verified by the rapid manufacturing micro-pit array experiment,and the results show the UEVC device has fine output stability.The residual height of the elliptical vibration assisted cutting surface in feed and cutting directions are analyzed,based on the mechanism of UEVC.On this basis,the elliptical vibration assisted cutting surface topography model is established,and it is verified by cutting experiment.Using the surface topography model established in this paper,the effects of vibration amplitude,cutting parameters and tool radius on geometric components of surface roughness are explained.Through micro-groove machining experiments,the restraining mechanism of ultrasonic elliptical vibration on material elastic recovery and plastic lateral flow during ultra-precision machining of titanium alloy are studied.Through cutting experiments,some factors like vibration parameters and cutting parameters that impact surface roughness are studied.Additional,the results indicate that the surface roughness value is fewer than 30nm,when the optimal process parameters are adopted.On the basis of the above research,the ultrasonic elliptical vibration assisted ultra-precision cutting experiment of titanium alloy is carried out with the optimized process parameter.The tool wear mechanism,chip formation mechanism,and machining surface quality in the ultrasonic elliptical vibration-assisted ultra-precision cutting process are studied,and compared with the traditional ultra-precision cutting experiment.Based on the above analysis,the influence of UEVC technology on the ultra-precision machining performance of titanium alloy is investigated.The experimental results show that,the reduction of tool wear,the improvement of machined surface quality,and the improvement of chip control are realized during the ultrasonic elliptical vibration assisted ultra-precision cutting mode,and the ultra-precision machining of titanium alloy is completed.Therefore,the UEVC technology greatly improve the ultra-precision machining performance of titanium alloy.Finally,an experimental study on the features of machined surface layer with titanium alloy in ultrasonic elliptical vibration assisted ultra-precision cutting is carried out,and compared with the conventional ultra-precision cutting.The features of the machined surface layer are tested and analyzed,using techniques such as profile method,scribing method,image processing,and microhardness testing.The mechanism of ultrasonic elliptical vibration on the plastic deformation,grain refinement,material phase change and microhardness of the machined surface layer are revealed.The experimental results show that,compared with the conventional ultra-precision cutting,under the ultrasonic elliptical vibration assisted ultra-precision cutting method,the plastic deformation depth of the machined surface layer is significantly reduced,the deformation area shows obvious compression deformation and it becomes more obvious as the speed ratio decreases.The depth of the grain refinement layer reduced.There is no obvious phase change in the machined surface layer.Additionally,the decrease of the work hardened layer is accomplish.The increasement of surface hardening degree of the machined surface is remarkable.The hardening degree of the machined surface rises conspicuously and continues with the decline of velocity ratio.