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Mid-Spatial Frequency Removal on Aluminum Free-Form Mirror

Author(s): Li, HY (Li, Hongyu); Walker, DD (Walker, David D.); Zheng, X (Zheng, Xiao); Su, X (Su, Xing); Wu, LZ (Wu, Lunzhe); Reynolds, C (Reynolds, Christina); Yu, GY (Yu, Guoyu); Li, O (Li, Tony); Zhang, P (Zhang, Peng) 

Source: OPTICS EXPRESS  Volume: 27  Issue: 18  Pages: 24885-24899  DOI: 10.1364/OE.27.024885  Published: SEP 2 2019   

Abstract: Mid-spatial frequency (MSF) errors challenge freeform manufacture, not in the least due to tool-misfit. This can compromise the performance of functional surfaces and is difficult to remove by post-processing. Our previously reported work on an effective process-chain for aluminum polishing demonstrated the ability to remove MSFs by hard-tool grolishing. In this paper, we describe MSF removal on an aluminum mirror, deformed to a saddle-like freeform shape, using power spectral density (PSD) as a diagnostic. CNC Precessions bonnet polishing was optimized to minimize output MSFs, then a non-Newtonian (n-N) tool was used to attenuate the residual MSFs that were present. Our approach was distinct from the approach pioneered by University of Arizona, in that we adopted small-tool polishing on the saddle-like part, with removal rate restored by rotating the n-N tool. In order to define the optimum window of rotation speeds, the dynamic behavior of the n-N material was explored by modelling and experiments. The tool was deployed on an industrial robot, and we describe a novel 'hyper-crossing' tool-path with wide sweeping paths, which is the logical opposite of the unicursal zero-crossing paths we have previously reported. This new path has proved ideally suited to robots, given their high velocity/acceleration capabilities. Detailed results are presented from the PSD viewpoint. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. 

ISSN: 1094-4087 

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