Research On Fabrication Of Micro-hole By EDM-ECM Combined Processing With Rotary Tube

With the development of the micro structure and system, micro holes with deep aspect ratio are widely used in in the field of aerospace engines, electronics industries, small medical equipment, etc. These micro-hole spare parts always adopt the materials difficult to cut, like stainless steel, cemented carbide, ceramics, etc. To ensure the performance of these part, micro holes should better be provided with deep aspect ratio and high accuracy as well as surface quality. Micro EDM and ECM are the most popular methods to fabricate micro holes, in which processing capacity is hard to satisfy all the need.Micro-EDM have high efficiency and the micro holes have deep aspect ratio. But there is recast layer on the surface of micro holes. While micro holes fabricated by micro-ECM have good surface quality. But the efficiency and aspect ratio is relatively low. Therefore, it is significant to combine both the advantages of micro EDM and ECM and develop an approach for the fabrication of micro holes by EDM-ECM combined processing. In order to obtain micro holes with high efficiency, deep aspect ratio and good surface quality, the method of micro EDM-ECM combined processing with rotary tubes is investigated in this work.Based on the analysis of the process conditions of micro holes combination requirements, the combination machining platform is established on the same machine. A special pulse generator for EDM-ECM combined processing is designed to improve machining efficiency. Besides, the fundamental experiments of the inner jetted dielectric micro holes with micro EDM are conducted on the combined processing platform; the EDM parameters such as current and capacitance are selected; the influence of these two main parameters on the machining efficiency and electrode wear is analyzed; the proper processing current and capacitance is selected. The unilateral clearance of micro holes fabricated with the above parameters is recorded, which provide the guidance for the further experiment.The simulation using Computational Fluid Dynamics( CFD) is applied to analyze the gap flow field of inner jetted dielectric micro holes machined by micro EDM. The gap flow models under different rushed hydraulic pressures and different spindle speeds are established and distribution regulations of micro holes EDM gap flow under different processing conditions are analyzed. Based on the results of simulation, the micro EDM experiment by tube electrode under different hydraulic pressures, spindle speeds and machine depth is conducted. Considering the results of simulation and experiment generally, increase hydraulic pressures make for the efficiency and electrode wear. While the gap flow field basically has no business with the spindle speed. But the experiment show that increase of spindle speed is conducive to enhance the efficiency because of the better discharge condition. There is always a relatively high fluid speed in the gap flow field, which probably is the main reason why the micro holes fabricated with tube electrode have high machine efficiency and depth.From the above simulation and experiment, the proper parameters in EDM is selected. To ensure an efficient combined processing, the reasonable neutral electrolyte is made using Na Cl O3 and 0.5wt% EDTA-2Na. The results of the experiment show that the surface quality and taper of micro holes machined by combined processing is more favorable than that by EDM. Then the experiment of combined processing is conducted with the 5mm 304 stainless steel to find a proper machining time(300s) of the best surface quality and taper. At last, the combined processing experiment is continuously conducted on the 3mm, 5mm and 7mm 304 stainless steel separately, in which the proper machining times are 180 s, 300 s and 480 s.