Development and Prospect of the Drilling and Detection of Film Cooling Holes on Turbine Blades and Vaves

Turbine blades are the core hot-end components for aeroengines, and machining film cooling holes on the blade body is essential for improving the temperature capability of turbine components. At present, the mainstream hole-drilling methods include electrical-discharged machining (EDM), electrochemical machining (ECM) and laser machining. Among them, the EDM hole-drilling process is the most mature and has the most obvious advantages in cost efficiency, which is widely used in various types of blades. ECM method satisfies the requirement of ‘no recast layer, no microcrack, no heat affected zone’, but the incapability of diffusor machining restricts its application. Long pulse laser was mainly used in hole drilling of stator and gas turbine blades. Recent years, with the rapid development of ultra-fast laser technology, the machining accuracy and quality of the hole wall have been significantly improved, making it also used in the hole making of blade rotor parts. Moreover, adopting abrasive flow, magnetic grinding and other film hole post-treatment processes could eliminate the sharp edge of the orifice intersecting line, and avoid the sharp edge cracking caused by the stress concentration effect. The engineering application of air film hole detection technology lags behind the processing technology, but it is of great significance for the quality control and the establishment of acceptance criterions for blade hole drilling. It is urgent to establish relevant standards to apply the advanced test and characterization methods to the engineering production, and to help the development of intelligent manufacturing technology in the long run.