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Proceedings Paper

Surface quality of a 1m Zerodur part using an effective grinding mode
Author(s): X. Tonnellier; P. Shore; P. Morantz; D. Orton
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Paper Abstract

A new ultra precision large optics grinding machine, BoX (R) , has been developed at Cranfield University. This machine is located at the UK's Ultra Precision Surfaces laboratory at the OpTIC Technium, North Wales. This machine offers a rapid and economic solution for grinding large off-axis aspherical and free-form optical components. This paper presents an analysis of surface and subsurface damage assessments of Zerodur(R) ground using diamond resin bonded grinding wheels. Zerodur(R) was tested as it is one of the materials currently under study for making extremely large telescope (ELT) segmented mirrors such as in the E-ELT project. The grinding experiments have been conducted on the BoX(R) grinding machine using wheels with grit sizes of 76 μm, 46 µm and 25 μm. The highest material removal rate (187.5 mm3/s) used ensures that a 1 metre diameter optic can be ground in less than 10 hours. The surface roughness and surface profile were measured using a Form Talysurf. The subsurface damage was revealed using a sub aperture polishing process in combination with an etching technique on small parts. These results are compared with the targeted form accuracy of 1 μm p-v over a 1 metre part, surface roughness of 50-150 nm RMS and subsurface damage in the range of 2-5 μm. This process stage was validated on a 1 metre hexagonal Zerodur(R) part.

Paper Details

Date Published: 25 September 2008
PDF: 9 pages
Proc. SPIE 7102, Optical Fabrication, Testing, and Metrology III, 71020B (25 September 2008); doi: 10.1117/12.797451
Show Author Affiliations
X. Tonnellier, Optic Technium (United Kingdom)
Cranfield Univ. (United Kingdom)
P. Shore, Optic Technium (United Kingdom)
Cranfield Univ. (United Kingdom)
P. Morantz, Optic Technium (United Kingdom)
Cranfield Univ. (United Kingdom)
D. Orton, Optic Technium (United Kingdom)
Cranfield Univ. (United Kingdom)

Published in SPIE Proceedings Vol. 7102:
Optical Fabrication, Testing, and Metrology III
Angela Duparré; Roland Geyl, Editor(s)

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