Quality Assurance of Turbines Blades with Optical 3D Metrology

Alconia Infinite Focus optical 3D measurement device used to examine cooling holes, edge geometries of the blade root and the air foil, as well as coating results.

This high-resolution optical measurement device is based on the principle of combining all the functions of a micro-coordinate measurement system and a roughness measurement device in a single sensor. In this way, users can measure both the geometry and the surface of turbine blades with just one system.

In the quality assurance of cooling holes, it is vital to verify that the angles, sizes, and shapes of up to 500 differently formed micro holes correspond exactly to their CAD data. Optical measurement with Focus-Variation is used to examine two areas in particular: the drill hole itself and where the drill hole transitions into the surface. Roundness, diameter, and angle at the transitions are especially relevant parameters. Measurement of the cooling holes at different positions is performed automatically by using special CAD/CAM software. Deviations from the target geometry are displayed instantly.

In addition to the 3D measurement of cooling holes, InfiniteFocus is used for edge measurement as well. Proper edge preparation of the leading and trailing edge of the airfoil ensures optimized aerodynamic properties and consequently makes the turbine more efficient. Edge measurement of the blade root is especially challenging, as it often involves a curvature with radii of varying sizes. Here, InfiniteFocus provides high resolution, traceable measurements in high repeatability.

Next to the measurement of micro holes and edges, roughness measurement is performed to verify coating processes. Before the coating is applied, an areal roughness measurement (Sa, Sq, Sz values) is carried out to verify that the surface of the turbine blade has been roughened properly. Then, after coating, coating thickness is verified by way of a difference measurement.