Shipboard applications of lightweight structures have increased over the past decade in both military and commercial vessels. Severe distortions have emerged as a major obstacle to the cost-effective fabrication of such lightweight structures. With a recent major initiative funded by the U.S. Navy Office of Naval Research, Northrop Grumman Ship Systems (NGSS) has undertaken a comprehensive assessment of lightweight structure technology. This program includes a comprehensive investigation of the fabrication and assembly processes for thin steel structures and their contributions to the final dimensional accuracy and distortion. As part of this effort, substantial work was done to characterize current dimensional quality performance in partial sub-unit (PSU) and combined partial sub-unit (CPSU) assemblies, and to identify contributing factors to dimensional inaccuracy and distortion in unit assembly stages. This information will be used by NGSS as a basis for improvements in fitting and welding processes, jigging and fixturing methods, dimensioning and tolerancing, and accuracy control processes. This paper summarizes the current dimensional quality performance in PSU and CPSU at NGSS, and the contributing factors to current performance.

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