Study On The Flow Field Of Ultrasonic Vibration Aided Electro-discharge Milling

The probability of short circuit and arc discharge in electro-discharge milling (ED-Milling) is large, which may reduce machining efficiency and quality. An effective way to solve these problems is introducing ultrasonic vibration, which can improve the liquid flow behavior, avoid depositing of molten particles and enhance pulse utilization. The study of flow field in the interelectrode gap of ultrasonic vibration aided ED-Milling can help understand basic rules of ED-Milling and effects of ultrasonic vibration, and provide some reference for studying dielectric breakdown, rules of surface roughness and material removal rate.Flow field in ED-Milling with ultrasonic vibration is systematicly studied by the method of theoretical analysis, simulation analysis and experimental verification.Mathematical models of2D-axisymmetric gap flow field and molten particles motion in Inner Jetted Dielectric ED-Milling are established, then simulation analysis are made by the software Fluent and verification experiments are carried out. Results show that velocity gradient and pressure gradient of flow flied increase with the increase of machining gap distance, rotating speed of tool-electrode and inlet pressure. The distribution of molten particles in machining gap is uneven. Rich regions of particles appear in left hand corner and right hand corner of machining gap, which can lead to secondary discharge and make the tool electrode into obtuse. When tool electrode rotates, molten particles are more easily removed out of machining gap, rate of short circuit decreases, material removal rate increases and surface roughness of workpiece decreases. With the increase of rotating speed of tool-electrode, tool electrode wear increases, but material removal rate increases small or remains the same.A theoretical model has been built in which the dynamic equation in the flow field is established and the pressure equations along X and Y directions are derived as well. Then simulation models are established and verification experiments are carried out. Results show that the pressure of liquid along X and Y directions in the flow field changes periodically at ultrasonic frequency because of the effects of ultrasonic vibration, which makes cavitation effect enhanced. Meanwhile the liquid flow behavior is improved substantially, the probability of short circuit and arc discharge is reduced, the machining stability and efficiency are improved, and thus the material removal rate of workpiece is enhanced. At the same time the depth of electric erosion pit is reduced, which in turn makes the molten metal on workpiece spread out more evenly, and finally the surface roughness of workpiece is decreased correspondingly. Molten particles are more easily removed when ultrasonic vibration is applied, which can reduce the concentration of molten particles in flow field, make molten particles move and homogenize, and then decrease tool electrode wear.Theoretical and simulation models of flow field of immersion ED-Milling and inner jetted dielectric+immersion ED-Milling are set up, and then verification experiments are carried out. The simulation and experimental results show that rich regions of particles exist in both ED-Milling. Machining efficiency and quality increases when tool electrode rotates. With the increase of rotation speed, tool electrode wear increases, but material removal rate remains the same or increases small. When ultrasonic vibration is imposed on tool electrode, the above variation tendency remains unchanged, but material removal rate increases and tool electrode wear decreases, which in turn make relative electrode wear reduce. Surface roughness of workpiece in inner jetted dielectric+immersion ED-Milling is decreased when ultrasonic vibration is applied, but surface roughness in immersion ED-Milling is increased.Silulation analysis and experimental comparison among different flushing ED-Milling are carried out. Results show that material removal rate of inner jetted dielectric ED-Milling is the highest, then is inner jetted dielectric+immersion ED-Milling, and last one is immersion ED-Milling. Tool electrode wear and relative electrode wear in turn is immersion ED-Milling, inner jetted dielectric+immersion ED-Milling, inner jetted dielectric ED-Milling.Surface roughness models verified by simulation analysis and verification experiments for ultrasonic vibration aided ED-Milling are set up. Results show that surface roughness decreases when ultrasonic vibration and other factors mainly affect parallel direction of finished surface in ED-Milling, while surface roughness decreases and then increases with the decrease of η1when vertical direction is affected.