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3.2.3 Computational Metrology of Manufactured Parts

Mark Levenson, Keith Eberhardt
Statistical Engineering Division, ITL

Steven Phillips, W. Tyler Estler, Bruce Borchardt, Daniel Sawyer
Precision Engineering Division, MEL

Marjorie McClain
Mathematical and Computational Sciences Division, ITL

Yin-Lin Shen
Department of Mechanical Engineering, George Washington University

Coordinate Measuring Machines (CMMs) are used to measure the physical dimensions of manufactured parts. Their ability to measure an almost endless variety of geometrically complex parts in a rapid and accurate manner has led to their widespread use in industry. However, the sophistication and flexibility of the CMM make assessment of the measurement uncertainty difficult. Developing reliable uncertainty methodology for CMMs would (1) promote improvement in quality and efficiency through better determination of part dimensions and (2) facilitate international trade that requires ISO 9000 compliance.

The five-year competence project on the traceability of Coordinate Measuring Machines ended in the last fiscal year (FY98). Some of the accomplishments of the project team are:

$\bullet$ The development of CMM traceability methodology geared towards a manufacturing production environment. The methodology Simulation By Constraint (SBC) greatly reduces time and cost over alternative methods of deriving uncertainty measures. It is being commercialized by private industry (see accompanying figure).

$\bullet$ A probe correction model. This model removes 90% of the systematic error in the most common class of CMM probes. The model results in a more accurate CMM without significant additional costs. The work was featured as the cover story in Quality Magazine, a widely read manufacturing publication.

$\bullet$ A software approach to calibrating CMMs that greatly reduces the time and expense of making the necessary measurements. The approach Supercrunch uses a global least-squares fit to extract the most information from a limited set of measurements.

As important as these tangible accomplishments are, the team has also developed a profound understanding of the uncertainty issues relating to CMMs and the manufacturing industry in general. The project has been a driving force in adapting and expanding traditional uncertainty methodology into new areas and bridging the gap to the uncertainty customers of industry. Presently, we are refining our previous work and moving into some new areas that promise to benefit the many U.S. industries that use CMMs.


Figure 9: VMIS Software, the commercial implementation of SBC methodology.

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Date created: 7/20/2001
Last updated: 7/20/2001
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