EDM ECM composite processes of high-quality small holes with large aspect ratios using tube electrode with innovative insulation structure

Traditional machining methods face significant challenges when processing small holes with large aspect ratios on hard-to-cut materials. At present, electrical discharge machining (EDM) remains one of the most effective methods for machining deep and micro-holes on hard-to-cut materials, but some problems, such as poor surface quality persist. Electrochemical machining (ECM) has the advantage of high surface quality; however, it is not as efficient or accurate as EDM in deep- and micro-hole machining. Therefore, combining EDM and ECM is one of the most effective methods for achieving high-efficiency, high-quality, and high-precision machining of deep- and micro-holes. This study first used the traditional EDM ECM composite processes method with a completely uninsulated tube electrode to machine deep and micro-holes. The experimental results showed that the outer surface of the tube electrode being completely uninsulated led to a decrease in the accuracy of the hole and a large difference in the diameters of the inlet and outlet of the hole. However, the use of a tube electrode with a completely insulated outer surface led to insufficient electrochemical machining of the hole wall surface, and there was still a large amount of residual recast layer from the EDM, resulting in poor machining surface quality. This study proposes a method for structured insulation on the outer surface of the tube electrode to improve the machining accuracy and surface quality of small holes with large aspect ratios. Three types of structured insulation tube electrodes are proposed: the axial electrolytic tube electrode, radial electrolytic tube electrode, and axial radial composite electrolytic tube electrode. The experimental results show that by optimizing the structural parameters of the insulation layer on the outer surface of the tube electrode, all three types of tube electrode can achieve high-quality and high-precision machining of small holes with large aspect ratios (> 50:1). The method of structured insulation on the outer surface of the tube electrode used in the proposed EDM ECM composite processes has broad application prospects for the machining of small holes with large aspect ratios on hard-to-cut materials.