Optical scanning slashes inspection times

Edited by the Engineeringtalk editorial team Jun 29, 2007

Centrax' Maxos optical scanning system has cut a customer's turbine blade inspection times by 97% compared to the co-ordinate measuring machine it was previously using.

Centrax has reduced the time required to inspect turbine blades 97% by switching from a co-ordinate measuring machine (CMM) to the Maxos optical scanning system.

"We originally planned to purchase several touch probe CMMs to keep pace with production during a ramp up of our blisk (blade integrated disk) manufacturing program", said Kevin Vickers of Centrax.

"But we discovered that the Maxos system is so much faster than the other machines we had considered that a single Maxos scanner handles our planned output".

Centrax' Turbine Components Division produces compressor and turbine aerofoils, discs, shafts, casings, associated hardware including sub assemblies and engine modules.

Blisks consist of rotor disks with integral blades or vanes for gas turbines.

One of a blisk's major advantages over the conventional disk and blade arrangement is the potential weight saving through the elimination of the fixings that secure the blade root to the disk.

One of the greatest challenges of producing blisks is inspecting them to ensure that they meet the very close required tolerances.

The conventional approach to inspecting blisks is with touch probe CMMs that are moved from point to point.

But this approach is very slow because the touch probe must make actual physical contact with each point that it measures.

The speed of the measurements is limited by how quickly the probe can be moved around the blade.

Noncontact scanners have recently been offered for this market that are faster but their weakness is that they cannot scan freshly machined or highly polished surfaces unless the surfaces are sprayed with a coating.

This need for a coating creates problems because it takes time, raises the risk of contaminating the blades and has released dimensional inaccuracy.

The Maxos scanner uses a proprietary noncontact probe consisting of a point of white light that allows the collection of individual points at a rate of 70 per second.

Like a touch probe CMM it collects individual points but unlike a conventional CMM it continues on its path at high speed and without pausing.

Because the Maxos scanner measures with a single white light point, the cause of inaccuracy and approximation inherent in 3D measurement with a ball probe is eliminated.

Consequently, Maxos has an exceptionally high accuracy of +/- 2um on matt surfaces and +/- 10um on polished metal.

It can achieve a point spacing resolution of 0.2um without pausing.

Additionally, since it has no ball probe and measures a single point at a time it is not limited by ball-offset geometry and can inspect radii of less than 0.2mm.

This feature is key to the measurement of leading and trailing edges on turbine blades.

The Maxos is a product of NVision in North America.