Mechanism of a deterministic sponge figuring processing (SFP) in Ni–P surface formation considering the robustness of the tool influence function: modeling and experimental investigation.

The core optics in the deep-space high-energy physics ray detection system are an ultra-precision aspherical surface, which would generate surface errors introduced by the ultra-precision single point diamond turning (SPDT), leaving the millimeter-level length and micron-level height periodic mid-spatial frequency (MSF) errors dissatisfying the expected optical performance. Hence, a corrective technique is urgent to effectively remove MSF errors from optical surfaces, enhancing the compliance control of the tool to adapt to curvature-varying optical surfaces to obtain a stable Gaussian-like removal function. This study explored the sponge figuring processing (SFP) removal mechanism, which verified the robustness and removal efficiency of the tool influence function for the planar and various curvatures of the Ni–P surface. To comprehensively investigate the removal function of SFP, based on the sponge-figuring process removal mechanism with three removal regimes, the relative velocity model and contact pressure model are established and verified for validity by pre-experiment. To obtain a stable and effective removal function, L16 orthogonal experiments and analysis of variance (ANOVA) methods were conducted on flat specimen surfaces on a 3-axis ultra-precision figuring tester machine utilizing a sponge head with in-situ correction of high slurry absorption and retention capacity as the figuring tool. To determine the curvature surface impact on the robustness of the tool influence function (TIF), matching experiments of spatial wavelength and full width at half maximum (FWHM) were executed. As a result, the removal function is mainly impacted by the offset, accounting for 40%, and the error was 8% in the predicted value of the volume removal rate under the optimal parameter conditions. From the perspective of optical performance, the significant peak of 1D-power spectral density (PSD) was suppressed in the mid-frequency band, partially converted into high-frequency band errors, and the mid-frequency surface ripple error was effectively enhanced from 2.4 to 1.8 nm, following multiple iterative figuring, for the variable curvature surface. [ABSTRACT FROM AUTHOR]