Breakthrough detection in electrochemical discharge drilling to enhance machining stability

Abstract

Film cooling holes are widely used in aero-engine turbine blades. These blades feature large numbers of holes with complex angles and require a high level of surface integrity. Electrochemical discharge drilling (ECDD) combines the high efficiency of electrical discharge drilling (EDD) with high quality of electrochemical drilling (ECD). However, due to the existence of a variety of energy for material removal, accurate and timely detection of breakthroughs is fraught with difficulties. An insufficient preset setting distance results in a tiny exit aperture, influencing the structure’s shape. In addition, the electrode is prone to bending at a large overfeeding distance, causing secondary discharge damaging sidewall surface integrity. This paper compares and analyzes the characteristics of processing waveforms using EDD and ECDD. A novel breakthrough detection method is proposed based on the variance signal of average voltage (VSAV) to increase machining stability and achieve fabrication without a recast layer. This method extracts the fluctuation transformation by calculating the variance of the average. Following signal detection, the overfeeding distance is quantified. An experiment is used to validate the breakthrough detection with 100% accuracy in all tests. The optimum overfeeding distances for hole angles of 0 °, 30 °, and 60 ° are obtained, and the stable removal of the recast layer is realized. Finally, the effectiveness of the method is verified on a typical workpiece with a double-wall structure and a nickel-based single crystal blade.