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Mary Bevan
Director, Corporate Communications

New Fabrication Method Improves Submarine Decks

This Fast Fit Structure metalworking innovation has been transferred for use on the U.S. Navy’s Columbia Class and on the first Virginia Payload Module. When steel is welded, it tends to curl. The goal is to make ship decks flat and smooth. Using finite element analysis, CTC engineers invented a way to add the proper curve to the beams and compensate for weld distortion so that, when the beams are welded and the clamps are removed, the deck structure is flat.

Johnstown, PA November 01, 2017

CTC engineers led a multi-million dollar Navy ManTech project titled “Self Locating, Self Fixtured Structures,” later consolidated to “Fast Fit Structure” by General Dynamics Electric Boat, that is contributing to the construction of Virginia and Columbia class submarine decks.

Over five years, the project is estimated to save more than $5 million. Life-of-program savings are estimated at over $28 million for the Columbia and Virginia class systems.

The Fast Fit Structure project resulted in a more efficient way of fabricating submarine deck structures, which have been traditionally constructed of many short, fitted pieces (intercostals) between continuous beams. Each piece requires a precise fit by highly skilled individuals.

The project team developed the manufacturing process for a new concept—the self-locating, selffixtured method—for fitting and joining the deck structures.

The self-locating, self-fixtured method will enable construction with notched beams that interlock and are continuous in both directions.

The team investigated manufacturing processes to determine the most efficient means of building these structures, and CTC engineers produced several test structures at the company’s Johnstown facilities, then transitioned the construction method and fixtures to Electric Boat’s Quonset Point facilities for the final three structures.

The details of the special notched joint and welding were refined with initial single cruciform trials, then applied to larger structures completed on a reconfigurable fixture.

All elements were combined and refined through several iterations of multi-beam trial structures, culminating with the large-scale trial—a 3 by 4 beam grid that is representative of a ship structure.

When steel is welded, it tends to curl and distort. The goal is to make ship decks flat and smooth. Using finite element analysis and a large, stiff structure, CTC engineers developed a way to add the proper curve to the beams and compensate for weld distortion so that, when the beams were welded and the clamps removed, the deck structure was flat.

CTC engineers developed, prototyped, and kitted the Fast Fit Structure project. When the kit was transitioned to General Dynamics Electric Boat, engineers who had no prior experience with the kit assembled the deck structure in just 17 minutes as compared to weeks the job used to require.

Other benefits:
• Part count (and associated handling costs) was reduced by 60 percent.
• Part shrinkage caused by welding was decreased by 77 percent.
• Flatness was improved by 90 percent over typical construction.

Implementation is expected on Columbia class and on the first Virginia Payload Module in the third quarter of FY19 at General Dynamics Electric Boat facility in Quonset Point. Current detail design has incorporated the self-locating, self-fixtured method in both programs.

Pre-Commissioning Unit Columbia (SSBN 826) will utilize the self-locating, self-fixtured method on 16 decks; subsequent ships of the class will incorporate it on 26-31 decks.

Both decks of the Virginia Payload Module will utilize the self-locating, self-fixtured method in their current design.

Team members included Columbia class Replacement Program Office (PMS 397); Virginia class Program Office (PMS 450); DDL OMNI Engineering Corporation; General Dynamics Electric Boat; Naval Surface Warfare Center, Carderock Division; the Navy Metalworking Center; and the Office of Naval Research ManTech Program.

This project was nominated by the Joint Defense Manufacturing Technology Program (JDMTP) Metals sub-panel for consideration as the ManTech Project of the Year. Although it didn’t win, the project received high praise from management at both the implementing shipyard (Electric Boat) and the government acquisition program office for the quality of work performed and the value to the U.S. Navy.

General Dynamics Electric Boat is pursuing followon projects with CTC that leverage the success of this effort to additional ship structures.