| With the use of sheet electrode to manufacture the special structures of deep and narrow grooves and complex die sinking by electrical discharge machining(EDM)method,it has been applied extensively in aerospace and mould industries.In order to better solve the problem of debris evacuation and improve the machining efficiency,we try to attach ultrasonic vibration to the tool electrode to investigate the effectiveness and feasibility of ultrasonic assisted EDM.The theoretical analysis and simulation calculation were carried out in this thesis,and the ultrasonic assisted EDM System based on tool electrode vibration was developed,finally the process experimental study was launched.The flow field in machining gap under the action of ultrasonic vibration of tool electrode was theoretically analyzed and simulated.Firstly,estimating the size of the gap between the poles,establishing the mesh model for FEA,determining the boundary conditions,defining the ultrasonic vibration of the electrode,and the velocity and pressure change law of the gap flow field in a sinusoidal period was obtained after the solution of Fluent.Then the ultrasonic amplitude,frequency,machining depth and gap value were analyzed by orthogonal experiment.The average value of velocity and the turbulent dissipation rate were chosen as the evaluating parameters,then the single factor experiment was launched and determining the ultrasonic amplitude and frequency as key variables.The results showed that the ultrasonic vibration had a pumping effect on the dielectric and accelerated its circulation flow,so that the flow of liquid could lead to the evacuation of the debris particles,but excessive disturbance would cause the particles accumulate in the corners,which indicated the effect of ultrasonic vibration on the actual machining process needs further test.Based on the theory of piezoelectric effect,the core component of the ultrasonic assisted EDM device: the sandwich piezoelectric ceramic transducer was designed by finite element method.The ultrasonic vibration of tool electrode was realized by the axial longitudinal vibration of the transducer.Using ANSYS Multi-physics module,the dry and wet modal analysis and harmonic response analysis were investigated,then the vibration mode and output response characteristics of the electrode end surface were analyzed.The impedance test,the vibration mode and vibration speed test,and the calibration of the amplitude output characteristics were carried out.The ultrasonic transducer power supply was built at the core of MOSFET.Finally based on the Hanchuan HCD400 K machine tool designed the interface equipment,and established the ultrasonic assisted EDM system.After debugging the system,we launched the experimental study of ultrasonic assisted EDM using sheet electrode.Taking the material removal rate,the relative electrode wear rate and the surface quality as the evaluating indicator,the response surface of the sheet electrode with the cross sectional area of 6mm×20mm was analyzed,then the influence of ultrasonic amplitude and conventional EDM parameters on the results was investigated.Then the electrodes with different cross-section shapes were made and theirs experiment were carried out,meanwhile the normal discharge rate was supplemented.The results showed that the ultrasonic vibration could effectively increase the normal discharge rate,the material removal rate could also be increased obviously at the smaller cross sectional area of the electrode,and the maximum machining efficiency could be increased by 35.9%,the electrode wear rate could be reduced simultaneously,and the quality of the machined surface was improved.It was proved that ultrasonic assisted EDM was an effective method to promote the machining rate and improve the processing quality when the cross sectional area and shape of the sheet electrode met certain requirements. |
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