Abstract

During subaperture tool grinding and polishing, overlaps of the tool influence function can result in undesirable mid-spatial frequency (MSF) errors in the form of surface ripples, which are often corrected using a smoothing polishing step. In this study, flat multi-layer smoothing polishing tools are designed and tested to simultaneously (1) reduce or remove MSF errors, (2) minimize surface figure degradation, and (3) maximize the material removal rate. A time-dependent convergence model in which spatial material removal varies with a workpiece-tool height mismatch, combined with a finite element mechanical analysis to determine the interface contact pressure distribution, was developed to evaluate various smoothing tool designs as a function of tool material properties, thicknesses, pad textures, and displacements. An improvement in smoothing tool performance is achieved when the gap pressure constant, $\bar h$ (which describes the inverse rate at which the pressure drops with a workpiece-tool height mismatch), is minimized for smaller spatial scale length surface features (namely, MSF errors) and maximized for large spatial scale length features (i.e., surface figure). Five specific smoothing tool designs were experimentally evaluated. A two-layer smoothing tool using a thin, grooved IC1000 polyurethane pad (with a high elastic modulus, ${E_{\rm{pad}}} = {{360}}\;{\rm{MPa}}$), thicker blue foam (with an intermediate modulus, ${E_{\rm{foam}}} = {5.3}\;{\rm{MPa}}$) underlayer, and an optimized displacement (${d_t} = {{1}}\;{\rm{mm}}$) provided the best overall performance (namely, high MSF error convergence, minimal surface figure degradation, and high material removal rate).

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Understanding and reducing mid-spatial frequency ripples during hemispherical sub-aperture tool glass polishing

T. Suratwala, J. Menapace, G. Tham, R. Steele, L. Wong, N. Ray, and B. Bauman
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Mechanisms influencing and prediction of tool influence function spots during hemispherical sub-aperture tool polishing on fused silica

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Modeling the hydrodynamic impact on the tool influence function during hemispherical subaperture optical polishing

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Appl. Opt. 61(18) 5392-5400 (2022)

Effect of workpiece curvature on the tool influence function during hemispherical sub-aperture tool glass polishing

T. Suratwala, J. Menapace, G. Tham, R. Steele, L. Wong, N. Ray, B. Bauman, M. Gregory, and T. Hordin
Appl. Opt. 60(4) 1041-1050 (2021)