A submarine propeller begins life as a greater than six-meter (20-foot) diameter, 50,000-kilogram (55-ton) metal casting. It must be machined down to a mass near 37,000 kilograms (41 tons) in its final form. Current machining methods leave the propeller with a rough surface, which if left unchanged, would betray a submarine’s movements in the ocean. 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 working 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. Additionally, refinements in the paths that the tool follows during metal cutting promise to substantially reduce roughness in the final milled propeller surface."