Abstract: Numerically controlled electrochemical machining (NC-ECM) for the pre-processing is a very important part of the combined electrical machining technology.This article discusses its key techniques, such as the design of cathodes and their moving tracks for machining a 3D-flow closed impeller, and proposes a new process of machining a cavity in the impeller by means of more than two cathodess. The 3D problem is simplified as into a 2D problem by stratification and superposition, and the machining surfaces of the cathodes are obtained by using the numerical method. Then the optimization of the cathodes cathode structure, the fixtures of cathodes, and the machining NC programs are completed. Furthermore, a series of technological experiments are made and a 3D-flow closed impeller is machined successfully by the combined electrical machining method. The test results show that the NC-ECM for the pre-processing is useful in production, raising the manufacturing efficiency by 40% while reducing electrode wear by 50% for electron discharge machining (EDM).

Key words: 3D-flow, closed impeller, curved cavity, electrochemical machining, cathodes