Browsing by Author "Baldwin, A."

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    Sub-surface damage issues for effective fabrication of large optics
    (2008-07-14T00:00:00Z) Tonnellier, Xavier; Shore, Paul; Morantz, Paul; Baldwin, A.; Walker, D.; Yu, G.; Evans, R.
    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
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    ItemOpen Access
    Subsurface damage in precision ground ULE® and Zerodur® surfaces
    (Optical Society of America (OSA), 2007-09-17T00:00:00Z) Tonnellier, Xavier; Morantz, Paul; Shore, Paul; Baldwin, A.; Evans, R.; Walker, D. D.
    The total process cycle time for large ULE®and Zerodur®optics can be improved using a precise and rapid grinding process, with low levels of surface waviness and subsurface damage. In this paper, the amounts of defects beneath ULE®and Zerodur®surfaces ground using a selected grinding mode were compared. The grinding response was characterised by measuring: surface roughness, surface profile and subsurface damage. The observed subsurface damage can be separated into two distinct depth zones, which are: ‘process’ and ‘machine dynamics