Robotic-Assisted Endoscopic OCT for Rapid, Non-Destructive Inspection of Turbine Film-Cooling Holes: A Proof-of-Concept Study

Film-cooling holes, typically 0.3–1 mm in diameter, are an essential feature of modern gas-turbine blades, sustaining an air film that shields the metal surface during high-temperature operation. Cooling performance depends sensitively on both the hole diameter and its drilling angle, yet conventional metrology such as X-ray computed tomography (CT) and stereo vision remains restricted by limited spatial resolution and depth-of-field, preventing reliable, in-situ characterization. In this paper, we report an optical inspection method that employs an ultra-thin endoscopic optical-coherence-tomography (OCT) probe. To suppress hand-induced oscillations and ensure repeatable insertion, the probe is mounted on a five-degree-of-freedom robotic platform. The resulting volumetric OCT data are processed to extract the inner-diameter profile and drilling orientation with single-digit-micrometer precision. Validation on additively manufactured turbine-blade coupons demonstrates a mean absolute diameter error of 4.3 µm (cylindri-cal)/5.1 µm (laid-back) and an angular error of 0.06°. Each hole is fully characterized in 48 s, making the method compatible with production. The proposed approach therefore provides a rapid, non-destructive quality-assurance tool for turbine components inspection.