Analysis And Experiment Research On Multi-physics Coupling Of Working Fluid In Ultrasonic Vibration And Magnetic Field Complex Assisted WEDM-LS

NiTi shape memory alloy is widely used in aerospace,biomedical and other fields because of its excellent fatigue resistance,corrosion resistance and biocompatibility.However,due to its special physical properties,the processing effect of traditional cutting and forming technology is not very satisfying.In order to overcome the difficulties in processing these special materials,WEDM-LS technology has been invented as the times require.It has no macro-cutting force,can be used to process conductive materials of any strength,and has high processing accuracy and high processing quality.Therefore,it is widely recognized in the processing of NiTi shape memory alloy.In order to solve the problems of low efficiency,poor stability and having difficulty in processing of large thickness workpiece of conventional WEDM-LS,ultrasonic vibration and magnetic field complex assisted WEDM-LS(USV-MF complex assisted WEDM-LS)is proposed in this paper.By studying the material removal rate and surface roughness under the influence of magnetic field and the working fluid flow field and temperature field under the influence of wire electrode ultrasonic vibration,the machining mechanism of this novel technology is explored.And then,the corresponding experiment is conducted to verify the feasibility of USV-MF complex assisted WEDM-LS in improving the processing efficiency and quality.Firstly,the influence of wire electrode ultrasonic vibration on discharge state,discharge stability,working fluid pressure and temperature are described,and the influence mechanism of the wire electrode ultrasonic vibration on processing performance is analyzed theoretically in this paper.The mathematical model of wire electrode vibration response of ultrasonic vibration assisted WEDM-LS(USV assisted WEDM-LS)is established,and the vibration state of the wire electrode is simulated in MATLAB,which lays a foundation for the establishment of multi-physical field coupling model of the working fluid in the machining area.Secondly,through the force analysis of a single electron in the discharge channel of magnetic field assisted WEDM-LS(MF assisted WEDM-LS),the motion trajectory expression of electron is deduced.On this basis,the material removal rate model under magnetic field is established,and the surface roughness prediction model is established based on the theory of material delamination removal.The effect of magnetic field on WEDM-LS is explained theoretically.Then,taking the working fluid in the machining area as the research object,the multi-physical field coupling simulation model of the working fluid was established,and the flow field and temperature field of the working fluid in USV assisted WEDM-LS were simulated and analyzed.A gas-liquid-solid three-phase flow model of bubbles,working fluids and debris particles in the USV assisted WEDM-LS machining area was established.The influence of ultrasonic vibration on bubbles and debris particles were investigated,and the process of bubble rupture was simulated.Finally,four kinds of machining experiments were carried out on NiTi-01 alloy,including conventional WEDM-LS,USV assisted WEDM-LS,MF assisted WEDM-LS and USV-MF complex assisted WEDM-LS.The effects of different machining technologies were analyzed and summarized from the aspects of discharge stability,wire amplitude,material removal rate,and surface quality of workpiece(surface roughness valve and three-dimensional morphology).The accuracy of material removal rate and surface roughness theoretical models were verified,and the reliability of the theoretical model is verified.