The turbine components division at Centrax Ltd. (Devon, England) produces compressor airfoils, discs, shafts, casings and other associated hardware, including complete subassemblies and engine modules.

One of the company’s signature products is the “blisk,” which consists of a rotor disk equipped with an integral set of blades for use in gas turbines. The product provides substantial weight savings, because it doesn’t require the use of separate fasteners to secure the blades. However, each blisk must be carefully inspected to ensure it meets the turbine industry’s extremely close tolerance requirements.

In the past, the company would use a touch probe coordinate measuring machine to perform the inspections. However, this approach proved to be very slow, because the probe had to make physical contact with every point being measured. The company would like to have used a noncontact scanner, but the systems typically fell short because they cannot scan freshly machined or highly polished surfaces unless the surfaces are sprayed with a coating. Obviously, having to apply the necessary coatings would increase inspection cycle times. The coatings also increase the risk of component contamination and introduce a new source of dimensional inaccuracy.

Ultimately, the company installed a MAXOS optical scanning system, manufactured by NVision Inc. (Southlake, TX). The MAXOS scanner uses a proprietary noncontact probe that employs a point of white light to collect as many as 70 individual points per second. Because of its exceptionally high accuracy-±2 microns on matt surfaces, ±10 microns on polished metal-the system can inspect the blades without having to use any kind of coating.

“We originally planned to purchase several touch probe CMMs to keep pace with production during a ramp-up of our blisk manufacturing program,” says Centrax engineer Kevin Vickers. “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.”

In fact, since going with the new MAXOS system, the company has been able to cut its blisk inspection time by 97 percent.

For more on inspection and coordinate measuring systems, call 817-749-0050 or visit www.nvision3d.com.