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Group Project Advances Rapid Blade Inspection

Ken Frescoln
By Ken Frescoln Business Development Manager, Aerospace Engine North America, Hexagon Manufacturing Intelligence

Record growth is shaping change throughout the aerospace and defense industry. Vast population growth, developments in emerging economies and increasing global political tensions are driving this boom cycle. Within this industry, the companies building airplane engines are facing huge order backlogs and looking for ways to speed the manufacturing process while maintaining the highest quality.

Today’s next-gen engine designs include highly complex 3D airfoil surfaces and creative new coating technologies. The new engines also deliver double-digit increases in fuel efficiency compared with early 2000s’ engine technologies. Inspection cycle times for these highly accurate rotating parts, using traditional contact scanning coordinate measuring machines (CMMs), are simply not fast enough to support customer demand. A new paradigm has unfolded, which requires non-contact metrology solutions that can equal the accuracy of traditional CMMs without the need to coat or spray part surfaces.

Existing non-contact measurement technologies, such as line scanners and optical 3D metrology systems, provide good repeatability but lack the high accuracy required for rotating parts—which are the most ubiquitous individual components in the engine. Airfoil surfaces are not only becoming more three-dimensional in nature, but the leading and trailing edges are becoming smaller. Also, tolerances across the entire surface are becoming much tighter, approaching +/- .001″ in some cases. In metrology terms, that means that the inspection device must be at least as accurate as 10% of the tolerance, requiring system accuracies of 2.5 microns.

The process of coating reflective or shiny surfaces to “dull” the part is a required step with many non-contact devices, making the metrology challenge significant. Because the coating process is manual, this process adds error. Spraying parts in order for these systems to function is a non-starter for the metrology system itself in a production environment due to the messy application and consequent cleaning process involved.

This problem has been studied for longer than three years in a partnership between companies making airplane engines, Tier One aerospace suppliers and Hexagon Manufacturing Intelligence. The research delivered a new non-contact point sensor (as opposed to point cloud sensors) that allows for the high accuracies required for rotating parts. The new technology is integrated into Hexagon’s HTA (High Throughput and Accuracy) product line designed to specifically address complex parts, such as compressor blades and vanes, blisks / IBRs and fan blades.

This non-contact point sensor called the HPO (Hexagon Probe Optical) uses a fiber optic laser source (in the infrared spectrum) to enable measurement of highly reflective surfaces. The sensor utilizes laser interferometry to determine where the part surface is, resulting in sensor repeatability of .2 µm (at 3-Sigma) on optical surfaces. This capability equates to the accuracy of the total system being dependent not on the sensor itself but on the CMM frame, matching accuracies seen in tactile scanning CMMs.

The nature of the infrared point sensor allows for a return signal on even the shiniest of surfaces, eliminating the need for part coating. Because the sensor collects data at a rate of 1,000 points per second, the new technology is delivering cycle time improvements in the area of 2-5 times, depending on the prior method.

The partnership nature of this project has resulted in technology that validates finished blades, removing bottlenecks and delayed output of new aeroengines. The system’s non-contact and high accuracy attributes are embedded into a shop floor hardened CMM design with parametric programming and a simple interface for the operator. The major leap for jet engine providers has been the step change improvement in measurement throughput, while concurrently integrating richer dimensional measurement data into production processes.

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