You are here

Low Cost Finishing of Optical Ceramic Domes with Embedded Grids


OBJECTIVE: The goal of this topic is to develop methods or techniques that will reduce the fabrication costs of optical ceramic domes containing embedded grids. DESCRIPTION: The Army has been developing large hemispherical domes for tri-mode seeker applications in current and future missile systems. The domes are made from hard optical ceramic materials such as aluminum oxynitride (ALON) and spinel. Several shielded designs incorporate metallic grids embedded within the optical ceramic material. With the tri-mode dome, the location of the embedded grid needs to be held to tight tolerance, plus or minus 1 mil, with respect to both the concave and convex surfaces. While finishing costs of traditional domes can approach half of the overall cost of the dome, finishing of the tri-mode dome could be significantly more expensive. This is due to the additional time and effort needed to maintain the position of the grid throughout the finishing process. It may be possible to compensate for the additional finishing time by reducing time elsewhere in the process. This could be from faster material removal, automated finishing, integrated grid tracking, or any other reasonable method that will save time and reduce cost. A significant reduction in the cost of optical finishing these domes could save the Department of Defense millions of dollars in procurement costs. The goal for this topic is to reduce the finishing cost by 50% which equates to one forth reduction in the overall dome cost. PHASE I: Evaluate the feasibility of reducing the cost of optical fabrication for ceramic gridded domes by a factor of two over tradition dome finishing. The study should include an analysis supporting the projection of a 50% reduction in optical fabrication costs for a full size gridded dome, and discuss how to achieve the tolerances goals in the Phase II. The evaluation should also include a demonstration of the fabrication technique on both flat coupons and curved surfaces. Biaxial flexure strength measurements should be performed on the polished flats to demonstrate that the new techniques do not compromise strength. The cost of the ceramic blanks should be included as part of the proposal. PHASE II: Use the techniques developed in Phase I to demonstrate a minimum 50% reduction in optical fabrication costs for a nominally seven inch diameter ceramic dome with embedded grid. The dome surfaces will be corrected to meet the 1/4 wave transmitted at 632.8 nanometers, center thickness to +/- 0.001 inches, radii center to center at +/- 0.0005 inches, and grid position to +/- 0.001 inches. The target radii, thickness, and grid position will be provided by the Army at the beginning of this phase. The gridded ceramic dome blanks should be included as part of the cost proposal either by procurement or by partnering with a dome manufacturer. PHASE III: Scale the processes developed in this effort to demonstrate production quantities and/or rates. This will be an enabling technology for future systems requiring the highest quality optics at an affordable price. Optical ceramics are used for a variety of missile domes and sensor windows. A factor-of-two reduction in the optical fabrication costs would result in significant savings for the Department of Defense. A small percentage of work at optical finishing house is government; therefore the techniques developed in this effort would most likely be used to process commercial orders for high quality optics as well. REFERENCES: 1] Harris, Dan,"Material for Infrared Windows and Domes,"ISBN 0-8194-3482-5, SPIE Press, 1999. 2] Warner, Charles, et al,"Characterization of ALON Optical Ceramic,"Window & Dome Technologies and Materials IX, Proceedings of the SPIE, Orlando, FL, March 2005. 3] Jian Yu, et al,"Processing Method and Process Modeling of Large Aperture Transparent Magnesium Aluminate Spinel Domes,"Defense, Security, and Sensing, Proceedings of the SPIE, Orlando, FL, April 2009. 4] A. LaRoche, et al,"Manufacturing issues for polycrystalline transparent spinel domes,"Defense, Security, and Sensing, Proceedings of the SPIE, Orlando, FL, April 2009. 5] Lee M. Goldman, et al,"ALON Optical Ceramic Transparencies for Window, Dome, and Transparent Armor Applications,"Window and Dome Technologies and Materials XII, Proceedings of the SPIE, Orlando, FL, April 2011.
US Flag An Official Website of the United States Government