Original Date: 07/21/2003
Revision Date: 01/18/2007
Best Practice : Accuracy Control and Three-Dimensional Measuring and Modeling
Electric Boat Corporation, Quonset Point Facility’s Accuracy Control and Three-Dimensional Measuring and Modeling processes are accomplished using four major steps: definition of measurement requirements; implementation and accomplishment of those requirements; evaluation of collected measurements; and adjusting the process to compensate for variation in interim-product assemblies.
Electric Boat Corporation, Quonset Point Facility (EBQP) defines Accuracy Control as “the measuring of selected dimensions during manufacture, assembly, and outfitting to allow in-process adjustments to ensure the final product meets the drawing requirements, readily fits to mating the parts and achieves system functional needs.” EBQP’s former processes during manufacture, assembly, and outfitting did not control accuracy, but rather accounted for inaccuracy within a nominal margin to allow for custom fit-up or “pairing” of large, dimensionally-complex assemblies. Much of the latter assembly work required on-board machining, which had a significant impact on the scheduled work for other trade areas. No data was gathered on the “as-built” condition of an area where a tight tolerance had to be met for another mating outfit assembly. The method of assembly was more system-oriented than modular, zone, or interim product-oriented. Using the previous method, typical cycle time for one submarine was approximately five years.
The current state-of-the-art process employs Accuracy Control and Three-Dimensional Measuring and Modeling to support modular, zone, and product-oriented design and construction. EBQP uses four major steps and a broad range of sophisticated hardware and software to accomplish these goals. Using the four steps of definition, implementation, evaluation, and adjusting with multiple tools allows flexibility in various applications so the most appropriate means can be used to achieve the best results. The four steps are further described as: definition of measurement requirements; implementation and accomplishment of those requirements; evaluation of collected measurements; and adjusting the process according to variation, the key for accurate assembly. Integrating the measurement results from multiple groups of dimensionally-complex assemblies is a significant challenge that requires a high degree of experience to produce quality major components that fit together without unintended interference. Considering the size, dimensional complexity, and weight of the assemblies that EBQP pairs without error is a world-class accomplishment. Delivery of a major submarine module having perfect tolerance at 99% completion and a reduction in cycle time to four years for the manufacture of one submarine are evidence of the world-class nature of this practice.
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