A proposed apparatus would effect friction stir welding (FSW) along a circumferential path to join two pipes. The apparatus is denoted an “orbital FSW system” because the circumferential motion of the FSW head would be similar to the motions of welding heads in commercial orbital fusion welding systems.

Unlike fusion welding, FSW involves large forces between the welding head and the workpieces. It is necessary to react these forces to prevent the workpieces from moving. Moreover, when the workpieces are pipes, they must be supported from within to prevent them from collapsing or undergoing undesired changes in shape when FSW forces are applied. The proposed system would provide the required motions of the FSW head plus the necessary support and reaction forces.

In FSW, a shouldered pin tool is plunged into the workpieces up to its shoulder with a controlled tilt and is rotated while being pushed or moved along the weld joint. The workpiece material under the tool becomes frictionally heated to plasticity, stirred, and pushed into place as the tool moves along, leaving behind the welded joint.

The proposed apparatus would include a FSW head with a retractable pin tool that would be actuated electrically, hydraulically, or pneumatically. The FSW head would be mounted diametrically opposite an external reactive roller on an external rotating assembly that would include circumferential driven gears in engagement with driving gears actuated by a motor. A roller assembly fixed to the sections of pipe to be joined would keep the external rotating assembly concentric with the pipes while allowing this assembly to rotate.

The apparatus would include internal reactive rollers located on the same diametral line as that of the FSW head and the external reactive roller. The internal reactive rollers would be driven to rotate along with the external rotating assembly in order to maintain this alignment. Thus, the internal reactive rollers would always be positioned to react the diametral FSW load and thereby prevent distortion of the pipes.

The apparatus could also be used to FSW solid rods, in which case the internal reactive rollers would not be needed or used. As described thus far, the apparatus would be used for FSW of pipes and rods with circular cross sections. However, because the apparatus would be computer-controlled and fully adjustable, it might be applicable to some noncircular cross sections.

This work was done by R. Jeffrey Ding and Robert W. Carter of Marshall Space Flight Center.

This invention has been patented by NASA (U.S. Patent No. 6,259,052). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to

Sammy Nabors
MSFC Commercialization Assistance Lead
at (256) 544-5226 or sammy.nabors@ msfc.nasa.gov.

Refer to MFS-31269.

NASA Tech Briefs Magazine

This article first appeared in the July, 2002 issue of NASA Tech Briefs Magazine.

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