As for machining film cooling holes in the turbine blades at the hot end of aero-engines

the research status in nearly a decade is reported about the electro discharge machining (EDM) of film cooling holes. The emphasis is focused on our innovation ideas and research progress in the electro machining processes and equipment technologies for solving machining problems of the film cooling holes with composite materials (high temperature alloy substrate and ceramic thermal barrier coating)

composite structure (circular hole section and diffusion structure section)

and low/no damage surfaces. Key methods and core technologies were researched and developed including a functional spindle head

a pulse power supply with high energy density

a servo control method of machining gap

a combined flushing system

and a method of drilling-penetration detection. The feasibility of three processes was verified including the hybrid process of EDM and ECM (electrochemical machining) for drilling the holes without recasting layers

the block divided EDM process for machining diffuser shaped structures

and the spark assisted chemical engraving (SACE) process for machining the thermal barrier coating of zirconia ceramic. The six-axis NC EDM equipment for machining film cooling holes was developed

which realized the automated machining process of straight holes and inclined holes with the drilling efficiency 20mm/min

dimensional accuracy better than ±20μm

and the controllable average thickness of recasting layer 10μm.