Precision Surfacing and Metrology of Naval Propellers

Abstract

This paper describes a novel approach to fabricating propeller blades to extremely high accuracy. The new approach includes iterative machining and rapid precision metrology. Iterative processes have been employed for decades in the optics industry. At Itek, robotics and computer-controlled surfacing techniques are used for iterative machining operations to produce ultra-precision optical surfaces. The technology developed at Itek for large optics has strong potential to transfer to the propeller industry. The surface of a propeller is difficult to measure accurately because of its odd shape and rapidly changing geometry, however, the Litton/Itek Surfitek Profilometer is capable of making this measurement to high accuracy. Surfitek was used to measure an Aegis Class Destroyer propeller blade to better than 0.001" over the entire surface. Data was obtained at an average rate of one point per second, manually, while rates of up to ten measurements per second are achievable under machine control. The system is capable of operating in contacting or non-contacting modes and includes software to calculate departures of the measured surface from the desired nominal, develop an error map of the measured surface and provide machine command control for an iterative manufacturing surfacing operation. The measurement equipment and data reduction techniques used in a propeller manufacturing demonstration, as well as the initial results obtained using iterative machining techniques arc discussed.