Ultrasonic Vibration Assisted EDM Surface Modification

Electrical Discharge Machining (EDM) is a machining method using electrical corrosion brought about by spark discharge between tool electrode and workpiece electrode to reach a certain size, shape and surface quality requirements. EDM is widely used in mold manufacturing, aerospace, electronics, precision machinery industry and so on to solute difficult processing of hard to machine materials and machining complex shapes.High energy density pulse discharge is used in spark surface strengthening technology to strengthen workpiece surfaces. In order to improve the physical, chemical and mechanical properties and extend the service life of workpiece, electrode material is penetrated into the surface of workpiece using pulsed spark discharge to form strengthening alloy film.Virtually, ultrasonic vibration is added to tool electrode or workpiece electrode on the basis of EDM to improve the processing conditions in ultrasonic vibration assisted EDM process.According to extensive experiments the influence of machine parameters such as reference voltage, pulse width, pulse interval, peak current on hardness, wear resistance, corrosion resistance of enhancement layer were investigated, especially the differences between the process assisted with the ultrasonic vibration or not were observed, at the end, the optimal process parameters can be obtained. The results show that the hardness of enhanced layer plays a major role in the decision of the the enhanced layer performance. Peak current affects the hardness of enhanced layer greatest, followed by processing time, pulse interval, pulse width. Pulse interval and pulse width have little effect on the hardness of enhanced layer. When the processing time is longer than a certain time, the microhardness of enhanced layer increases firstly and then decreased with the peak current increases,. With the processing time increases, the condition is the same with the peak current increases.Silicon tool electrode is used to strengthen the surface of carbon tool steel and form a film of silicon and silicon compounds on the workpiece surface with the appropriate pulse discharge parameters and ultrasonic vibration parameters. Test results show that the hardness, wear resistance, and corrosion resistance of workpiece surfaces after surface strengthening are significantly improved that helps to improve the performance and service life of the workpiece materials. Cavitation, eddy current effect and the pump suction of ultrasonic vibration make the product of electrode erosion more refined and uniform. Metallurgical reaction is occurred between electrode material after refining and workpiece surface and integrated together. Boundaries of the electrical discharge strengthening blur and the quality of strengthing surface is improved.