QMT Features: February 2013
Herculean measurement
 Lockheed Martin engineers build Hercules aircraft right the first time when they use laser trackers and handheld scanners


It’s called Hercules – the oldest and most versatile military aircraft product line in aviation history. First built by Lockheed in 1954, the C-130 has flown to both poles, supported missions in the Congo, Vietnam and Kosovo, and has even retrieved satellites in mid-air. And today, the quality control engineers at Lockheed Martin Aeronautics use API laser trackers to ensure this legendary aircraft’s quality and precision.

Lockheed Martin has three laser interferometer trackers manufactured by API on hand in its 900-acre plant in Marietta, Ga., – two Tracker 3 models and one of API’s latest, the Radian. They are all managed and maintained by quality control analyst staff Paul Davis, who has been overseeing quality control for Lockheed Martin for the past seven years, coming to the aerospace giant after more than 20 years working in various machine shops.

Working in a manufacturing facility that employs  about 7,200 people  on four aircraft or subassembly lines, Lockheed Martin needed to be sure that the aircraft components are absolutely consistent. Laser trackers were brought in the past decade as part of then-executive vice president and Marietta general manager Lee Rhyant’s mission to modernize the site’s manufacturing technology.

A matter of time
Of course, the C-130 has been built long before laser trackers were introduced to Lockheed Martin. Davis said he remembers those days when five workers were needed to run theodolites, requiring hours of set-up and suffering from the constant mistakes or miscalculations that humans inevitably make.

“Everything was done optically. You had to use piano wire, optics and levels,” he recalled. “And you had to have multiple measurements of everything to be sure.”
When laser interferometer technology started appearing in aerospace facilities in the 1990s, Davis was immediately convinced.

“I thought it was the best thing ever,” he said. “The amount of time to do anything is reduced in and out. It’s quicker, the accuracy and errors are reduced. The metrology is tremendous.”
Part of the convenience of laser trackers is their portability. The Radian in particular weighs less than 20 lbs (9 kg) and is about 7 inches wide by 14 inches tall – roughly the size of a shoebox.
1,200 holes in one hour

The value of API trackers is especially evident when the Lockheed Martin team inspects aircraft bulkheads. These panels have thousands of holes drilled into them and each one must be inspected carefully to ensure it is property aligned. Using API’s handheld scanning accessory, the Intelliscan 360, an inspector can check the position of 1,200 holes in one hour.
API trackers are not only used to measure and inspect the aircraft. They are more often employed to check the tools and machinery that work on the aircraft. Davis tests every tool used in the construction of the plane, thereby giving Lockheed Martin engineers the confidence that they are getting things right the first time they build them.

“All the machinery is validated by the API tracker,” Davis said.”All the tooling is inspected with the tracker. A tool does not get used for production unless we give it the blessing 100 percent with the laser tracker.”

Volumetric Error Compensation
Lockheed Martin was the first company in the world to employ API’s Volumetric Error Compensation (VEC) solution to test the validity of its five-axis milling machines. This solution ensures that the movements of machine tool across all six degrees (x, y, z, pitch, yaw and roll) are accurate and can even actively compensate through the machine’s controllers any errors in movement or angles.
VEC represents a massive change from Lockheed Martin for machine tool measurement. API was only selected after a thorough evaluation that proved the system’s advantages over common calibration practices, including the use of piano wire to measure movement.

Saving more time
Another advantage of using a laser interferometer tracker is its ability to level to gravity, Davis said. This saves workers from having to bring in an optical level to ensure the accuracy of the aircraft’s construction. Using reflectors to assess the levelling, the tracker can measure a 130-foot envelope within one two-thousandth of an inch, and repeat that measurement six times. Davis said he saves a tremendous amount of time. “It takes one minute to level. The laser tracker is unique in its ability to do that,” Davis said.

The Radian has a large opening angle of 360° horizontal and +/- 70° vertical, allowing for a wide range of measurements. Regardless of the task at hand, every job performed by an API laser tracker is at the industry’s highest standard of accuracy. The interferometer, which comes standard in every Radian and Tracker 3, is a first-tier measurement device that measures distance counting the number of light wavelengths, which is a far more accurate measure of distance than those that rely on timing or other mechanisms. The interferometer is designated by the National Institute of Standards and Technology as a “first tier” measurement, meaning it meets an internationally accepted standard of accuracy.

The use of laser trackers will only continue to improve the process at Lockheed Martin and allow for greater innovation, Davis said. The only challenge is that everyone will have to keep up.
“As technology changes, the ability to manufacture to tighter tolerance changes,” he said. “And everybody’s job changes.”l
www.apisensor.com

 

  
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Rob Tremain Photographer
www.4exposure.co.uk
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