Automatic complete high-precision optical 3D measurement of air cooling-holes of gas turbine vanes for repair

Abstract

High-resolution contactless optical 3D measurements are well suited for determination of state and position of gas turbine vane cooling-holes during maintenance rework. The air flow through the cooling-holes protects the turbine vanes from the high temperatures. However, the coating needs to be renewed during repair of the vanes. The renewal process can lead to partially or completely filled cooling-holes. This paper describes a newly developed procedure to automatically detect and reopen such holes by laser-drilling for an effective new repair process. The turbine vane is scanned by a fringe projection based optical 3D scanner. The resulting 3D pointcloud delivers plenty of detail to automatically detect the cooling-holes. Poorly detected or undetected cooling-holes are interpolated from properly detected neighboring cooling-holes and reference default cooling-holes. For the resulting laser-drilling process the precise orientation in the vane mount must be known. To this end, position and orientation of the scanned vane in relation to the reference vane is determined. To validate the approach, numerous experiments regarding the cooling-hole extraction-performance were satisfactorily conducted. Real drilling experiments confirmed those findings and were used to validate the entire process.