Abstract
In this paper, considering the effects of the characteristics of the three-phase flow dielectric in the discharge gap flow field on the discharge channels in the ultrasonic vibration and magnetic field assisted low speed WEDM (USV-MF assisted WEDM-LS), the model of discharge channel including discharge position and size of discharge channel is established. Firstly, a mechanism of bubble-particle bridging breakdown was proposed under working condition of cutting workpieces with large thickness. Then a prediction model of the discharge point position in USV-MF assisted WEDM-LS under three-phase flow dielectric characteristics based on the breakdown mechanism was performed, and FEM software COMSOL was used to simulate and analyze this model. By comparing with the experimental results of discharge point position captured by high-speed camera, the accuracy of the prediction results of discharge point position in USV-MF assisted WEDM-LS was verified, it showed that the model can explain the dielectric breakdown more accurately. Next, the model of radius of discharge channel including magnetic field intensity, electric field intensity, medium pressure, and surface tension of discharge channel was established, and the influence of USV and MF on the size of discharge channel was analyzed theoretically. The radius of discharge channel in USV-MF assisted WEDM-LS was obtained by solving the partial differential equation in MATLAB. According to discharge point position and radius of the plasma discharge channel, surface morphology of workpiece was simulated by COMSOL. Finally, the experiment of photographing the discharge channel in USV-MF assisted WEDM-LS was carried out to verify the above model. It showed that the trend of the simulated results of discharge channel position is the same as that of the experimental results, and the error of peak height value between simulated and experimental results is within 6%.
Highlights
WEDM is a non-traditional machining technology, in which a continuously moving electrode wire is used as tool electrode to produce spark discharge heat between electrode wire and workpiece to melt materials
Discharge model based on a bubble-particle bridging breakdown mechanism Because workpiece with large thickness in WEDM-LS is considered in this paper, the debris removal condition will be greatly affected by the thickness of workpiece, which causes some erosion products enter the discharge channel with bubbles generated by discharge
It is shown that the USV-MF assisted WEDM-LS can reduce the occurrence of concentrated discharge during the WEDM and increase the discharge success rate
Summary
WEDM is a non-traditional machining technology, in which a continuously moving electrode wire is used as tool electrode to produce spark discharge heat between electrode wire and workpiece to melt materials. Chen et al [3] studied the motion trajectory of electron beam and debris in magnetic field assisted WEDM It indicated that additional (extra) constant magnetic field can increase the discharge crater volume and the expel efficiency of charged debris, which improved the machining quality. The time-varying radius model of discharge channel in USVMF assisted WEDM-LS was built and the influence of ultrasonic vibration and magnetic field on the radius and size of discharge channel was analyzed. An experiment of photographing the discharge channel in the USV-MF assisted WEDM-LS of workpiece with large thickness was accomplished, and the results show that the discharge channel characteristics in USVMF assisted WEDM-LS of can be predicted well by the above model
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