Deep-type hole machining by inner jetted aerosol dielectric ablation

Abstract

To improve the stability and technological index for deep hole machining by electrical discharge machining (EDM), this study proposed a hole machining method that employs continuous flushing and intermittent oxygen feeding (i.e., inner jetted aerosol dielectric ablation). Aerosol, a mixture generated by oxygen and water, was used as the discharge dielectric when the oxygen was supplied. The released chemical energy was used to improve the efficiency of deep hole machining during the machining of ablation. The ablation surface was trimmed by EDM at the anaerobic stage. A comparative test for inner jetted aerosol dielectric ablation, inner jetted dielectric EDM, and intermittent EDM ablation in pure oxygen (designated as intermittent EDM ablation) was performed in deep hole machining. In this paper, we studied the mechanism, machining efficiency, electrode relative wear ratio, and machining quality and accuracy. The energy of intermittent EDM ablation was excessively high that it cannot be easily controlled. The erosion products blocked the inner hole of electrode during machining. This phenomenon prevented oxygen from entering the machining region and induced short-circuit occurred, thereby causing the instability of deep hole machining. Inner jetted aerosol dielectric ablation can effectively control the degree of ablation and stabilize the process. The hole with a side length of 4.4 mm can be machined successfully, and its depth can reach more than 70 mm under the experimental conditions. The machining efficiency was 5.45 times that of the inner jetted dielectric EDM, and the relative tool wear ratio decreased by 82 %. Overall, the process showed excellent surface quality and high machining accuracy.