| Low speed wire electrical discharge machining(WEDM-LS)is a common high-precision special machining method,in machining TiNi shape memory alloy(SMA),the mechanical stress and vibration problems affecting the machining accuracy are avoided.However,the traditional WEDM-LS processing of TiNi SMA has some problems,such as low processing efficiency and poor surface integrity.Therefore,a complex WEDM-LS process of ultrasonic vibration and magnetic field is proposed in this paper.Taking the self-generated magnetic field of electrode wire as the medium and the influence mechanism of ultrasonic vibration and additional magnetic field on the self-generated magnetic field as the starting point,the analysis of the coupling characteristics of magnetic field between poles is completed.Combined with theoretical modeling and process experiments,the composite mechanism of ultrasonic vibration and additional magnetic field is studied,the processing mechanism of composite process is analyzed,and finally the processing law and reliability of composite process are summarized.Firstly,the coupling mechanism of the inter pole magnetic field is analyzed,the best coupling mode of the inter pole magnetic field is determined,and the influence mechanism of ultrasonic vibration and additional magnetic field on the self-generated magnetic field of the electrode wire is explored.Based on the vibration response equation of electrode wire,the ultrasonic vibration assisted WEDM-LS self-generated magnetic field model is established.The magnetic field coupling model is established by applying additional magnetic fields in different directions.The results show that ultrasonic vibration,magnetic field and machining direction will significantly change the distribution and intensity of inter pole magnetic field.Secondly,taking the self-generated magnetic field of the electrode wire as the bridge,the coupling simulation of the magnetic field between the electrodes is carried out,and the influence of the additional magnetic field in different directions on the magnetic field of the discharge gap is analyzed.The three-dimensional simulation analysis of self-generated magnetic field with ultrasonic vibration assisted WEDM-LS is carried out,and the spatial superposition of self-generated magnetic field is studied.The self-generated magnetic field under complex working conditions is simulated based on MATLAB,and the distribution law of self-generated magnetic field in the span of electrode wire under different process parameters is summarized.The simulation results show that the magnetic field will make the workpiece with high relative permeability produce greater magnetization;Ultrasonic vibration and additional magnetic field can greatly improve the strength of self-generated magnetic field and inter pole magnetic field.Then,the single pulse heat source model is modified based on the inter pole magnetic field model,the temperature field simulation of the workpiece is completed,and the shape and position change process of the discharge crater is analyzed.The simulation results show that under the ultrasonic vibration and magnetic field assisted WEDM-LS,the coupled magnetic field deflects the discharge channel,which changes the shape and position of the crater generated by the discharge,that is,the depth and width of single crater increase by 11.3% and 15.3% on average,and finally improves the material removal rate.Finally,different process experiments are completed.Taking workpiece surface roughness,machining speed,material removal rate and surface integrity as the objects,the composite machining mechanism and process law are analyzed,and the magnetic field coupling verification test is designed.The experimental results show that the combination of ultrasonic vibration and magnetic field WEDM-LS has the best surface integrity and maximum machining efficiency;The magnetic field effectively suppresses the vibration amplitude of the electrode wire and improves the value of surface roughness.At the same time,the magnetic field coupling between poles is the main action mode of ultrasonic vibration and magnetic field combination.It verifies the accuracy and reliability of the self-generated magnetic field model and magnetic field coupling model,and reflects the superiority and feasibility of the combination process. |
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