Inspection and process-control improvements achievable with a testing tool developed at the National Institute of Standards and Technology recently prompted the Boeing Commercial Airplane Group to enter into its first-ever cooperative research and development agreement with a federal laboratory.
NIST and the Seattle-based maker of passenger jets, the largest Boeing Co. unit, will focus initially on NIST's easy-to-use system for regularly checking the performance of coordinate measuring machines, or CMMs. Potentially, the technology could be applied to all of the some 130 CMMs installed in six of Boeing's nine divisions. There, the automated measuring machines are used to inspect the dimensions of parts that the company makes or buys from suppliers.
Called the NIST interim testing artifact, the modular, lightweight system consists of a pair of inexpensive, calibrated ball bars (two steel spheres connected by a steel bar) that are kinematically mounted on rotatable aluminum arms. The base is screwed into inserts on a CMM table, and the baton-like ball bars are rotated from one indexed position to another. At each position, the CMM takes a series of preprogrammed measurements, and the results are compared with known values.
To ensure measurement accuracy, Boeing currently calibrates its CMMs periodically, according to the performance history of each unit. This is a costly process that can take from four days to two weeks. In between calibrations, the NIST interim testing artifact can greatly enhance a CMM operator's ability to quickly ascertain the performance of the machine and its subsystems.
"The data-collection and analysis process is so quick—a complete system check-up can be accomplished in less than half an hour—that weekly performance evaluations are practical," explains Edward Sergoyan, an engineer for BCAG Operations Technology, the commercial unit's research and development arm.
The greatest virtue of the artifact, however, may be its thoroughness. It includes all CMM subsystems, which usually are calibrated separately, into one measurement profile. "The way the system is configured allows you to uncover subtle problems that might not be identifiable during separate calibrations," Sergoyan says. The interim testing artifact provides such a reliable performance check, he adds, that it could allow Boeing to recertify its CMMs on an as-needed basis, rather than according to a predetermined schedule.
During initial research testing of a prototype unit at a Boeing facility, the artifact's practical value quickly became apparent. While demonstrating their innovation, Steven Phillips, NIST CMM program manager, and his team first discovered measurement errors on a CMM and then pinpointed the cause—a faulty mechanism preventing the measurement probe head from locking into place. Currently, a pneumatically controlled version of the artifact—adaptable for use on various types and sizes of CMMs—is being evaluated at three Boeing fabrication facilities.
Soon a fully automated, computer-integrated version will undergo trials at Boeing. NIST also is supplying the company with calibrated ball bars from 300 millimeters to 1.5 meters long so that the system can be used to evaluate a range of CMMs.
Boeing's interest in the NIST testing artifact stems from the measurement intensiveness of aircraft manufacturing and the company's increasing reliance on CMMs for inspection tasks. According to Sergoyan, about 30 percent of the 4 million parts that make up a Boeing 747 passenger jet are inspected on CMMs. Boeing's newest jet, the 777, contains somewhat fewer parts, but, he says, 70 to 80 percent of those parts undergo CMM inspection.
While NIST and its partners continue to work on more advanced prototypes of the interim testing artifact, several Boeing divisions already are convinced of the technology's utility. They placed orders for commercial versions of the pneumatic system, made by Giddings and Lewis Measurement Systems, Dayton, Ohio.
After applying an early prototype of the testing artifact in a project to develop adaptive methods to enhance CMM accuracy (an effort co-funded by NIST's Advanced Technology Program), Giddings and Lewis chose to commercialize the technology. The first products based on the NIST design recently have been released.
Meanwhile, Boeing is exploring applications of the testing artifact in manufacturing process control. Increasingly, manufacturers are incorporating measurement probes into their machine tools, enabling in-process inspection of part dimensions. But problems can arise. For example, a machine's frame may be out of square or its scale may be miscalibrated, resulting in inaccurate measurements that easily escape notice.
As it does for CMMs, the interim testing artifact offers an independent means of assessing the performance of measurement equipment on machine tools.
Encouraged by the prospects for the CMM-focused collaboration, Sergoyan describes Boeing's new relationship with NIST as a "good union," good enough to warrant exploring cooperative work in other manufacturing technology areas.
As a non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.