1 June 2002
Sub plan at full steam
Charlotte, N.C.—Supersmooth propellers allow submarines to run silently in deep water, but the problem is the nickel-aluminum-bronze alloy blades take up to a year to make. That's too long, the Navy says.
So high-speed machining experts have surfaced from the National Institute of Standards and Technology (NIST) and the University of North Carolina at Charlotte to work with the Navy on a new machine tool and special metal-cutting strategies to decrease that time to four months.
A submarine propeller begins life as a >6-meter diameter, 50,000-kilogram metal casting. Experts machine it down to a mass near 37,000 kilograms. Machining methods leave the propeller with a rough surface that could betray a sub's movements. So months of hand finishing are required.
"Such a time-consuming process may soon be a thing of the past," said Tony Schmitz, a NIST engineer on the project. "NIST's tool wear and surface finishing experiments have led to a better understanding of the required parameters for high-speed machining of the propeller alloy. These discoveries have enabled us to increase the material removal rate during machining by a factor of 10.
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