Cooling holes inspection

Measuring System: SurfaceInspect
Keywords: aerospace industry, energy industry, turbine blades, HPT shrouds, gas combustion engines

To help avert heat-related  failure of combustion engines, multiple small cooling holes are drilled into hollow turbine blades to discharge cooling air from the blade interior onto its surface. Cooling hole geometries have grown more complex over time to improve their functional effectiveness.

Novacam’s SurfaceInspect provides advanced capabilities in cooling holes inspection. The non-contact inspection system acquires high-precision 3D topography of surfaces at high speed (2,000 to 30,000 points per second). In a single pass over a turbine blade, the system scanner acquires a 3D point cloud of the surface, enabling the characterization of:

  • The shape of the diffuser opening
  • A portion of the cooling hole inner diameter (ID) (which can be further extended by varying the scanning angle)
  • The geometrical center of the through hole
  • The inclination angle of the through hole
  • The profile, waviness, and roughness of the acquired bottom surface of the cooling hole
  • Dimensional variability of each hole with respect to a CAD model.

This cooling hole diffuser opening reveals the dual channel shape created by drilling (point cloud acquired by SurfaceInspect)

This cooling hole opening reveals the dual channel shape created by drilling. (Click for a close-up)

Fitting a cylinder to the bottom surface of each cooling hole helps determine the cooling hole center-line and inclination angle of the through-hole

Fitting a cylinder to the bottom surface of each cooling hole helps determine the cooling hole center-line and inclination angle of the through-hole. (Click to see close-up)

Flexible installation

The SurfaceInspect system is based on low-coherence interferometry technology. It is a modular and fiber-based optical system; its scanner is connected to the signal-processing profilometer with an optical fiber that can be hundreds of meters long. As such, the scanner is easily integrated as either a robot arm end-effector or as a 3D vision component in automated or semi-automated systems on the plant floor. It is even rugged enough to withstand hostile environments.

Inspecting cooling holes in tight spaces

Unlike microscope-like instruments, the SurfaceInspect system can also be configured to measure surfaces in hard-to-reach spaces. While the standard galvo scanner that comes with the SurfaceInspect is the fastest scanning option, a small-diameter rotational scanner can also be added or substituted to acquire cooling holes in tight space such as, for example, on the inner surfaces of stator blades.