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Please use this identifier to cite or link to this item: http://dspace.lib.cranfield.ac.uk/handle/1826/7364

Document Type: Conference paper
Title: Sub-surface damage issues for effective fabrication of large optics
Authors: Tonnellier, Xavier
Shore, Paul
Morantz, Paul
Baldwin, A.
Walker, D.
Yu, G.
Evans, R.
Issue Date: 2008
Citation: X. Tonnelliera, P.Shorea, P.Morantza, A.Baldwin, D.Walkerc, G.Yuc and R.Evans. Sub-surface damage issues for effective fabrication of large optics. Proceedings of SPIE Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, Monday 23 June 2008, Marseille, France. Vol. 7018, 70180F. Eds. Eli Atad-Ettedgui and Dietrich Lemke
Abstract: A new ultra precision large optics grinding machine, BoX®has been developed at Cranfield University. BoX®islocated at the UK's Ultra Precision Surfaces laboratory at the OpTIC Technium. This machine offers a rapidand economic solution for grinding large off-axis aspherical and free-form optical components.This paper presents an analysis of subsurface damage assessments of optical ground materials produced usingdiamond resin bonded grinding wheels. The specific materials used, Zerodur®and ULE®are currently understudy for making extremely large telescope (ELT) segmented mirrors such as in the E-ELT project.The grinding experiments have been conducted on the BoX®grinding machine using wheels with grits sizes of76 μm, 46 μm and 25 μm. Grinding process data was collected using a Kistler dynamometer platform. Thehighest material removal rate (187.5 mm3/s) used ensures that a 1 metre diameter optic can be ground in lessthan 10 hours. The surface roughness and surface profile were measured using a Form Talysurf. The subsurfacedamage was revealed using a sub aperture polishing process in combination with an etching technique.These results are compared with the targeted form accuracy of 1 μm p-v over a 1 metre part, surface roughnessof 50-150 nm RMS and subsurface damage in the range of 2-5 μm. This process stage was validated on a 400mm ULE®blank and a 1 metre hexagonal Ze
URI: http://dx.doi.org/10.1117/12.790639
http://dspace.lib.cranfield.ac.uk/handle/1826/7364
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