Surface Roughness Tuning at Sub-Nanometer Level by Considering the Normal Stress Field in Magnetorheological Finishing.

Xiaoyuan Li,Yunfei Zhang,Qikai Li,Chao Wang,Minheng Ye,Zuoyan Ye

doi:10.3390/mi12080997

Xiaoyuan Li, Yunfei Zhang + Show 4 more

Open Access

https://doi.org/10.3390/mi12080997

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Journal: Micromachines	Publication Date: Aug 21, 2021
Citations: 8	License type: CC BY 4.0

Affiliation: China Academy of Engineering Physics

Abstract

Although magnetorheological finishing (MRF) is being widely utilized to achieve ultra-smooth optical surfaces, the mechanisms for obtaining such extremely low roughness after the MRF process are not fully understood, especially the impact of finishing stresses. Herein we carefully investigated the relationship between the stresses and surface roughness. Normal stress shows stronger impacts on the surface roughness of fused silica (FS) when compared with the shear stress. In addition, normal stress in the polishing zone was found to be sensitive to the immersion depth of the magnetorheological (MR) fluid. Based on the above, a fine tuning of surface roughness (RMS: 0.22 nm) was obtained. This work fills gaps in understanding about the stresses that influence surface roughness during MRF.

Highlights

Fused-silica optics are integral to high-energy laser systems such as the wedged-focus and beam-sampling lenses at the National Ignition Facility (NIF) at Lawrence LivermoreNational Laboratory (LLNL) [1]
Magnetorheological finishing (MRF) is a novel kind of finishing technique that uses magnetorheological fluid consisting of carbonyl iron powder (CIP) in a basic liquid containing polishing grains [6,7]
Contrast immersion depth, the increase of0.2 the stresses wereroughness not obviFigure shows that when the immersion immersion depth was0.2 mm, surface roughness (Rq) was reduced from

Summary

Introduction

Fused-silica optics are integral to high-energy laser systems such as the wedged-focus and beam-sampling lenses at the National Ignition Facility (NIF) at Lawrence LivermoreNational Laboratory (LLNL) [1]. Fused-silica optics are integral to high-energy laser systems such as the wedged-focus and beam-sampling lenses at the National Ignition Facility (NIF) at Lawrence Livermore. Producing fused silica optics with high-quality surfaces can reduce the scattering of laser energy and localize thermal focus, greatly enhancing the laser-induced damage threshold (LIDT) of the laser system [2,3]. Though the surface roughness of the fused silica can be improved to the sub-nanometer level via the chemical-mechanical polishing (CMP) [4,5], the frequent iteration of this method induces a low processing efficiency. MRF is widely considered to be a deterministic method to finish optics to an extremely high surface quality [8]. During the MRF process, a shear force dominates material removal; the relationship between the material removal rate (MRR) and force fields have been well investigated over the years [9,10,11,12]

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