High-quality and high-precision machining of small hole with large aspect ratios using variable-parameter composite EDM/ECM processes with speed limit

Traditional machining methods face significant challenges when machining small holes with large aspect ratios in difficult-to-machine materials. Currently, combining electrical discharge machining ( EDM) and electrochemical machining ( ECM) is one of the most promising methods for achieving high-efficiency, high-quality, and high-precision machining of deep microholes in difficult-to-machine materials. In this study, an axial-radial composite electrolytic tube electrode was used to machine a small hole with a large aspect ratio. However, because of the long machining time required for small holes with large aspect ratios, there was a significant difference in the electrolysis times at the inlet and outlet of the hole, resulting in a large difference between the inlet and outlet diameters of the hole. To solve this problem, this study investigated a variable-parameter composite EDM/ECM process. Experimental results showed that both the processing speed and electrical parameters had significant influences on the hole diameter, and simply increasing the electrical parameters did not decrease the hole taper. To achieve high-quality and high-precision machining of small holes with large aspect ratios, this study investigated a variable-parameter composite EDM/ECM process with speed limit using tube electrodes with innovative insulation structures. The experimental results showed that when using the variable-voltage composite EDM/ECM machining process with a speed limit, small holes with a large aspect ratio and almost zero taper (-0.01°), or even a negative taper (–0.115°), were successfully machined. In addition, no EDM residuals were found at the hole outlet, and the wall surface of the hole was smooth. The Ra value of the hole-wall surface was lower than 0.5 μm. The proposed method has broad application prospects for machining high-quality and high-precision small holes with large aspect ratios in difficult-to-machine materials.