Mid-spatial frequency removal on aluminum free-form mirror

Hongyu Li, David D. Walker, Xiao Zheng, Xing Su, Lunzhe Wu, Christina Reynolds, Guoyu Yu, Tony Li, Peng Zhang

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


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.
Original languageEnglish
Pages (from-to)24885-24899
Number of pages15
JournalOptics Express
Issue number18
Early online date19 Aug 2019
Publication statusPublished - 2 Sep 2019


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