Concentrated precision: CMM Inspection

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END USER: Delta TechOps, (866) 676-3358, www.deltatechops.com. CHALLENGE: Maximize accuracy and efficiency in inspecting complex turbine engine blades and vanes. SOLUTION: Measurement system utilizing concentrated light. SOLUTION PROVIDER: NVision Inc., (972) 393-8000, www.nvision3d.com

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Delta TechOps, the technical operations division of Delta Air Lines, is the largest airline maintenance, repair and overhaul provider in North America and the third largest worldwide. In addition to maintaining the Delta aircraft fleet, Delta TechOps serves more than 150 aviation customers, specializing in high-skill work such as engine, component, airframe and line maintenance.

Delta TechOps maintains a variety of turbine aircraft engines as well as turbine-driven, ground-based auxiliary power units. The company disassembles engines and routes components to different parts of the organization for inspection and repair.

The area that handles turbine blades and vanes deals with a vast number of complex components. According to Cameron Leonard, lead aviation maintenance technician, an engine can contain 1,300 to 3,000 blades and vanes. “Depending on the engine, how long it has run and other parameters, we have to measure features such as the chord, axial chord and root of a component to make sure it is airworthy or if it needs repair,” he said.

Tolerances are commonly within 0.001 “, and various measurement technologies are employed, including micrometers, calipers and nondestructive testing methods such as fluorescent penetrant, X-ray and ultrasound. “It all depends on what the manufacturer requires,” Leonard said.

Some of the complex 3-D contours of the blades are challenging to consistently and quickly measure. Manual measurement is time consuming, and results can vary from technician to technician.

Delta TechOps sought a way to increase the speed and consistency of the measuring process by examining measuring systems that were more applicable to its parts. Laser-based measuring was one alternative, but the shiny surfaces of the blades can cause a laser beam to speckle, or scatter. As a result, laser measurement required that the component be sprayed with a nonreflective coating that, Leonard, said, “is more trouble than it is worth.”

Another possibility, automated touch-probe technology, suffered in precision when measuring the sharp edges of the blades, because accuracy is dependent on ball-offset geometry related to the size of the touch stylus vs. that of the edge being measured.