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.