A sustainable, high-quality method for machining film cooling holes: Cryogenic airflow-assisted electrochemical discharge drilling

Abstract

Film cooling hole is an essential part of aero-engines, necessitating without recast layer, no stray corrosion, and high machining efficiency. Its sustainable manufacturing has been at the forefront of industrial focus. Existing machining methods have problems such as low efficiency and environmental hazards. In order to achieve the production requirements of precision, quality, and green simultaneously, an external cryogenic airflow-assisted electrochemical discharge drilling (ECDD) is proposed. Compared with the current electrochemical drilling (ECD) or electrical discharge drilling (EDD), a glycol working fluid with ultra-low conductivity neutralizing salt replaces the high conductivity of acidic solution or spark oil to realize green machining without a recast layer. Compared to existing ECDD, the introduction of cryogenic gas with glycol can significantly reduce stray corrosion and achieve exceptionally high surface quality. In the theoretical part, the influence mechanism of a low-temperature environment on the electrochemical interface was analyzed by using the electrochemical analysis technique. In addition, a multi-physical field simulation model was established, which was finally verified by experiments. Finally, the surface characteristics were analyzed by using TEM. The results demonstrate that the cryogenic environment enhances the passivation effect, as evidenced by a 35% reduction in taper at 258 K and a 28.2% decrease in stray corrosion. The hole side has nano-roughness (Ra 0.512 μm). Notably, the material removal rate does not significantly diminish at low temperatures and achieves 0.1 mm/s, superior to EDD. As there is no need for an additional machining step after drilling, this method proves its characteristic to attain sustainability, efficiency, and high quality, indicating promising application prospects.