Joining the giant aluminum alloy plates used on large ships and spacecraft usually requires teams of workers with handheld arc welders. But having to rely on human labor can cause costly delays, and manufacturing companies are eager to develop new methods. One of the most promising is friction-stir welding, which uses a spinning rod to generate enough heat to soften the aluminum and to push the alloy's molecules together with 15,000 pounds of pressure. A friction-stir welding machine moving at 8 inches a minute can join inch-thick alloy plates in a single pass, while traditional arc-welding would require over a dozen welds to complete the same seam.

But the technology does have a downside: The machines need extra hardware to absorb the intense pressure, known as Z-force. Bulky and expensive, the hardware limits the length of the welds and often relegates friction-stir welding to big-dollar government programs in need of precise joins, such as the Navy's Littoral Combat Ship and NASA's Ares I-X test rocket, which lifted off in late 2009.

A new tool called a bobbin may help make the method mainstream by simultaneously joining the plates and absorbing pressure. Next-generation friction-stir welding devices could weld steel, combine heterogeneous metals and make welds of indefinite length by perching bobbins on dollies that move along lengthy seams.

HOW IT WORKS:

Friction-stir welding joins metal with heat and high pressure. A new tool called a bobbin could make the technique quicker and more practical.

1. The bobbin's shoulders, working like a vise, stabilize 1-inch-thick aluminum alloy plates.

2. The rotating head, spinning at 275 rpm, generates friction heat that softens the metal along the path of the weld.

3. The pressure that merges the metal is absorbed by the bobbin instead of by separate machinery.

4. The rotation of the tool leaves concentric circles on both sides of the joint.

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