An electrochemical discharge drilling method utilising a compound flow field of different fluids

Abstract

To fabricate small holes in a nickel-based single crystal superalloy without formation of recast layer and stray corrosion, electrochemical discharge drilling utilising a compound flow field of different fluids (DF-ECDD), is investigated in this study. DF-ECDD is a compound machining method that electrical discharge machining (EDM) and electrochemical machining (ECM) can occur simultaneously in the process. In this method, the internal flushing of a low-concentration salt solution and external flushing of a deionized water occur simultaneously. By means of the internal flushing, EDM and ECM occur synchronously in the process. Owing to the external flushing, the conductivity of the solution on the surface of the workpiece is significantly reduced, thus reducing the stray electric field distribution. In this study, the influence of the conductivity of the external flushing liquid in the DF-ECDD process was analysed. The simulation results showed that when deionized water with a conductivity of 2 μS/cm was used as the external flushing liquid, the stray current on the workpiece surface was almost completely eliminated. Furthermore, the expression is theoretically derived for the relationship between the radii of the stray corrosion areas and the conductivity of solution domain. The experiments verified that the radii of the stray corrosion areas decrease with the decreasing of external flushing liquid conductivity. Finally, the stray corrosion could also be almost eliminated with the DF-ECDD process, and the machined holes were free of recast layer.