A novel backflushing method for improving machining quality in electrochemical discharge drilling

Abstract

Film cooling holes work in an extremely high temperature, high pressure, and alternating load. The recast layer is not allowed on the wall side. Electrochemical discharge drilling (ECDD) is a promising nontraditional method in aerospace manufacturing to obtain a high surface quality, offering high efficiency in theory. However, a shortage of working fluid near the hole exit after penetration is inevitable, leading to poor stability and surface quality, and the current processing methods make it difficult to drill small holes with high quality. Hence, a novel backflushing ECDD (BF-ECDD) method has been proposed. Backflushing is a certain conductivity liquid. It flows continuously along the backside of the workpiece during the entire process. When the hole is penetrated, the backflushing liquid flows from the exit to the entrance along the inter-electrode gap, improving the flow field and effectively solving the problem of liquid solution shortage. It helps to strengthen the electrochemical dissolution near the hole exit and improve the hole quality. Here, the method is shown to be feasible, and a conductivity matching relationship between the working and backflushing liquids is studied with simulation and comparison experiments on a nickel-based single crystal material. The results show that BF-ECDD can reduce the occurrence of short circuits by 68 % and enhance the stability of the penetration stage. The flow rate in the machining gap is more than doubled, and the taper angle is eliminated. Finally, it meets the extreme manufacturing needs of the entire hole without recast layer with high efficiency.