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Turbine blade: "fir tree" inspection

Marketing Team

The perfect flow profile of a turbine blade is a technical masterpiece – its complex geometry poses a challenge to metrological quality assurance. With the optical measuring station MarSurf CWM 100, Mahr offers the measuring solution for testing coated, uncoated, polished as well as mirror finished surfaces so that production remains reliable and repeatable.

Complex components for heavy loads
Turbine blades can be found in many sectors: in aircraft engines of the aerospace industry, stationary gas turbines in the energy industry or in compressors in engine construction. In daily use, they are subjected to high stresses due to the radial movement under centrifugal force – both mechanically and thermally. The optimum efficiency of these components depends on the shape of the blade and the surface texture or roughness of the surface. The defined tolerances must be continuously checked during production.

Challenge "fir tree profile"
Turbine blades are mounted by their root in the turbine ring or turbine disk. This root is often designed as a "fir tree profile" because of the high centrifugal forces. These profiles are sanded and their surface quality has to be checked.

Measuring solution: non-contact optical testing technology
The MarSurf CWM 100 optical 3D measuring system operates as a confocal microscope and white light interferometer, allowing it to adapt to any surface microstructure. In this case, it is also possible to detect the various test points on the surface of the curved blade contactlessly with sub-nanometer resolution.


CNC-controlled tilt/swivel device
In microscopic measuring systems generally, an orthogonal alignment is required of the surface to be inspected with the optical axis of the lens. In practice, the complex geometry of turbine blades significantly complicates orthogonal alignment. For repetitive tests on identical workpieces, such a test can only be carried out sensibly with CNC-automated measuring stations. The MarSurf CWM 100 from Mahr with its CNC-controlled tilt/swivel device makes testing considerably easier. Due to the total of five degrees of freedom of the positioning axes, the point to be measured on the turbine blade can almost always be reached without difficulty – be it the blade surface itself, the edges of the blade or the outlet of the cooling canals.

Quality assurance according to ISO 25178
Form and roughness can be determined with this measurement solution, as well as the characteristic roughness parameters such as Ra, Rz, Rq, Sa or Sq according to ISO 25178. The measuring system is suitable for technical, optical and reflective surfaces and reliably measures coated, uncoated, polished and mirror-finished turbine blades.

Fully automatic testing
The computer-controlled measuring system MarSurf CWM 100 with its CNC-controlled tilt/swivel device enables the fully automatic testing of the turbine blade. The measurement results are then evaluated by the high-performance MarSurf MfM software. Of course, this can also be done with an automatic tolerance evaluation, e.g. which also optically indicates whether the surface values are within or outside the tolerance.

Value: fast, reliable information on production quality

  • Fast and precise multiple positioning even of complex geometries with the tilt/swivel device
  • Optical measurements within seconds
  • Fully automatic surface inspection via CNC control
  • All surface structures can be measured

Advantage: Short measuring times – more efficiency

  • Shortened measuring times
  • More efficiency in quality assurance
  • Improvement of production quality
  • Reduction of rejects
  • Production is more economical

More information on the measuring microscope MarSurf CWM 100 can be found here...



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