Electrical discharge machining of Ni-based superalloy and its applications in aero turbine parts: a comprehensive review

Nickel-based superalloys have been used in aero-engines for turbine blades, vanes and other engine components due to their excellent high-temperature properties, such as creep resistance and fatigue properties. Various aero-engine components like cooling holes in vanes, nozzle guide vanes, seal slots, blisks, fir tree slots etc. are being machined by EDM/w-EDM (wire Electrical Discharge Machining) in high aspect drilling and complex shape generation. Hence, research is needed to improve the productivity, surface integrity and process capability. Generally EDM and w-EDM are employed to generate fine holes and contour respectively. Recast layer formation and micro-cracks in HAZ (Heat Affected Zone) are the most common hazardous phenomenon visible in cooling holes. But Hybrid multi-axis w-EDM helps in minimising the width of HAZ in aeroengine components. It helps in formation of recast layers less than 0.0004 of an inch and surface roughness in submicron range up to 0.5 micron. High-speed w-EDM is recommended by ADMAP-GAS project for the finishing operation in manufacturing of fir tree slots as it doesn’t leave a burr. Heat shield holes are efficiently machined through ultrasonic vibration-assisted EDM. Repeatability, shape adherence and process capability in EDM is found to be better than any other machining processes of aero parts.

镍基高温合金（Nickel-based superalloys）凭借优异的高温性能（如抗蠕变性能与抗疲劳性能），已被广泛应用于航空发动机的涡轮叶片、导叶及其他发动机部件的制造。诸如导叶冷却孔、喷嘴导叶、密封槽、整体叶盘（blisks）、枞树型榫槽等各类航空发动机部件，目前多采用电火花加工（EDM, Electrical Discharge Machining）与线电火花加工（w-EDM, wire Electrical Discharge Machining）进行高深径比钻孔及复杂型面加工。因此，亟需开展相关研究以提升加工效率、表面完整性与工艺能力。通常而言，电火花加工与线电火花加工分别用于加工微细孔与型面轮廓。在冷却孔加工过程中，热影响区（HAZ, Heat Affected Zone）内形成的重铸层与产生的微裂纹是最为常见的有害缺陷。而混合多轴线电火花加工可有效缩减航空发动机部件热影响区的宽度，能够实现厚度小于0.0004英寸的重铸层，以及最高可达0.5微米的亚微米级表面粗糙度。ADMAP-GAS项目推荐采用高速线电火花加工进行枞树型榫槽的精加工工序，因其不会产生加工毛刺。超声振动辅助电火花加工可高效加工隔热屏孔。研究表明，电火花加工在加工重复性、形位符合性与工艺能力方面均优于航空零部件的其他加工工艺。