Simulation And Experimental Study On The Fabrication Of The Composite Electrode For MEDM

With the development of the increasing precision and miniaturization of products in the world wide, the micro electric discharge machining (MEDM) technology to drill micro holes has been widely used in many technology fields, such as aerospace, micro electronics industry, medical instrument, mould manufacturing and so on, because of the characteristics of the high-precision regardless of material properties. However, when under the micro machining conditions, especially with the increasing machining depth, it is very difficult to remove gaseous bubbles and debris from the discharge gap with the scale of several microns, leading the unstable machining process and excessive electrode wear, which has serious effect on the dimensional accuracy and the shape accuracy, and even result in tool wear instead of deep drilling because abnormal discharges occur frequently. As a result, systematically studying the micro hole MEDM technology is a continuously developed and deepened subject which is very comprehensive and complex.Based on the similarity analysis and theoretical modeling, a computer simulation model was adopted to research the process of drilling holes using MEDM and was compared with the actual machining process. Experimental results and simulation results consistently showed that during the machining processing of drilling holes, there were material loss at both the end and the side of the tool at different degrees. The corner wear in the end of tool electrode was so serious that the angularity becomes blunt, resulting in the taper shape; and this phenomena was more and more serious as the increase of the processing depth. Based on the aforementioned analysis results, a simulation model for drilling micro holes using MEDM with composite electrode was proposed and the simulation results showed enhancing the electrical erosion resistance of surface material was able to effectively decrease the tool wear of the side surface, especially at the angularity of the end of the tool electrode; therefore, the end could approximately realize the uniform wear, and remarkably improve the shape accuracy of the machining micro holes.On the analysis of the simulation results, a new composite electrode was fabricated and used to drill the micro holes using MEDM instead of the traditional electrode to maintain the tool electrode shape unchanged. A different type of material, Ni-W alloy, which has the high electrical erosion resistance, was coated on the substrate surface of the Cu electrode, and preliminary experiments of drilling micro holes using MEDM have been carried out. Experimental results strongly indicated the rationality of simulation analysis; and also showed that because of the Ni-W alloy coating, the tool wear on the side, especially on the corner of the end was decreased significantly. As a result, there was obvious promotion of those to maintain the electrode shape unchanged and enhance the shape accuracy of the drilled holes.Some beneficial attempts have been made to simulate and study the processing of drilling micro holes using MEDM in this paper based on the theory of the single pulse discharge, which could provide a different method to analyze the tool wear of different types of electrodes and the influence on the micro holes during the processing to some extent. According to the simulation results, a new type of composite electrode was fabricated, and this can be a good example to develop new type of tool electrode in order to further improve the machining accuracy of the micro holes.