TECHNOLOGY AREAS: Ground/Sea Vehicles, Materials/Processes

ACQUISITION PROGRAM: PMS 501 (LCS Program), PMS 325 (JHSV Program), PMS 377 (LHA (R))

OBJECTIVE: The objective of this project is to develop and demonstrate a robust, transportable system for the assembly and joining of large, complex structural aluminum components using friction-stir welding as the joining process. These assembly operations are situations where the use of large, stand-alone friction welding systems is physically impossible. Shipyards assemble the superstructures of lightweight ships from pre-fabricated stiffened aluminum panels. Sub-contractors construct these panels from aluminum strips, extruded profiles, et cetera, by linear friction-stir welding. Shipbuilders assemble these pre-fabricated panels using traditional arc welding techniques which leads to distortions, loss of strength in the weld-zone, and potentially introduces defects into the structure.

DESCRIPTION: The friction-stir welding process requires the application of relatively high forces to the structure. These joints are generally "out of position" in that they are not exactly vertical or horizontal along the outside of the structure. They are often in locations with limited accessibility, and since the structures require unique setups, this prohibits using large and complex fixtures to support the components during the joining process. Because of this, the joining process requires considerable adaptability and flexibility whilst maintaining carefully controlled joining conditions that remain in the acceptable processing window. This topic seeks innovative approaches to extend the applicability of friction stir welding beyond the standard linear friction stir welding capability for the pre-fabrication of stiffened aluminum panels. The scientific and engineering solutions to enable "out-of-position" friction stir welding capability during assembly, erection, and repair of structural sub-components in shipbuilding must address the essential design elements for broad applications, adaptability to various assembly scenarios, and maximum accessibility (that is a combination of transportability and reach and access). They must address the essential control elements for set-up and manipulation, and the ability to react welding forces induced during the process. They must also address essential welding elements to produce consistently and reliably sound welds in marine structures for the materials, applications and assembly scenarios previously identified.

PHASE I: In the phase I effort, the investigators should define operating conditions required for friction-stir welding of components. These will include the orientation of the tool, the positioning of the welding head, estimation of position tolerances allowable, and the forces expected during the operation. The investigators will then design a welding system that is capable of meeting these requirements in a shipbuilding environment. Full success will be a concept of operations and preliminary drawings of the system, with specifications for many of the major components, for evaluation.

PHASE II: Develop and demonstrate a functional prototype system. Conduct testing in a shipyard environment to prove feasibility of the system for the application.

PHASE III: The immediate application of the developed system is to shipyards constructing lightweight, high-speed ships such as the LCS and the JHSV. A successful system may also be useful to shipyards constructing internal aluminum partitions of modules within combatants, such as the aluminum command-and-control spaces in the current-construction CVN. The system should also be applicable to the construction of lightweight ground vehicles.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The shipyards may apply this technology directly to commercial ship fabrication. In addition, this type of capability has significant non-shipbuilding potential. Industry could use a flexible joining capability for aluminum structures for the fabrication of trailers and rail cars. In specific, industry might use this technology for the fabrication of coal-cars and grain-cars, which carry bulk cargo. This technology is also applicable to the fabrication of bulk aluminum enclosures and storage containers. All of these are economically important industrial applications where reduced construction costs and increased durability lead to reduced life-cycle costs and improved competitiveness.

REFERENCES:
1. C. Smith, Chapter 11, Robots & Machines for Friction Stir Welding/Processing, beginning page 219, Friction Stir Welding & Processing, Edited by R. S. Mishra & M. W. Mahoney, Published by ASM International, January 2007.

2. B. Halverson, J. Hinrichs, Friction Stir Welding (FSW) of Littoral Combat Ship Deckhouse Structure, Presented at 2006 SNAME Maritime Technology Conference & Expo - October 10 - 13, 2006 - Fort Lauderdale, FL.

3. K. Colligan, Low-cost friciton stir welding of aluminm for littoral combatant ship applications, Proceedings for the 8th International Friction Stir Welding SYmposium, 18 - 20 May 2008, Timmendorfer Strand, Germany.

KEYWORDS: Friction-stir welding; aluminum; shipbuilding; aluminum fabrication; robotics; automation.

** TOPIC AUTHOR (TPOC) **

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