Experimental study on surface integrity and subsurface damage of fused silica in ultra-precision grinding

Yaoyu Zhong,Feng Shi,Hang Xiao,Yifan Dai

doi:10.1007/s00170-021-07439-y

Abstract

The surface quality and subsurface damage (SSD) distribution achieved with a fine-grained grinding wheel under different depth-of-cut and cutting speed is experimentally studied. The ground surface roughness (SR) is investigated via white light interferometry and expressed in terms of four typical roughness values (PV, RMS, Rz, and Ra). The SSD is characterized by the magnetorheological finishing (MRF) spot method and transmission electron microscopy. The results show that brittle-ductile surfaces and ductile-like surfaces are generated during ultra-precision grinding. Largely due to plastic flow removal, fracture defects such as fractured pits and grinding streaks on the ground surface can be mitigated. Instead, a ductile-like surface covered with grinding streaks is found. When the depth-of-cut decreases from 4 to 1 μm, the SR and SSD depth decreases from PV 1.34 μm, Ra 15.23 nm, Rz 0.94 μm, RMS 22.24 nm, and SSD 6.1 μm to PV 0.51 μm, Ra 5.07 nm, Rz 0.24 μm, RMS 6.70 nm, and SSD 1.2 μm. In addition, when the cutting speed increases from 3.9 to 23.4 m/s, the SR and SSD depth decreases from PV 1.03 μm, Ra 15.01 nm, Rz 0.82 μm, RMS 21.43 nm, and SSD 5.6 μm to PV 0.12 μm, Ra 3.17 nm, Rz 0.07 μm, RMS 4.65 nm, and SSD 0.003 μm. Moreover, the material removal mechanism under different grinding parameters is revealed by calculating undeformed chip thickness, and the mechanism of surface morphology and subsurface crack produced in brittle-ductile mode is analyzed. A linear relationship between the SR and SSD depth is in accord with the formula SSD = 0.41Ra−0.68 for brittle-ductile surfaces.

Highlights

Fused silica has been widely utilized in the fabrication of large laser facilities, such as inertial confinement fusion (ICF), due to its unique optical, mechanical and thermal properties [1,2]
When exposed to high fluences in the ultra violet range, some defects on the fused silica will evolve into damage precursor induced laser damage, which make the lifetime of fused silica decreases rapidly [3,4]
To estimate Subsurface damage (SSD) depth influenced by the coexistence of brittle fracture and plastic flow, Ra is the most appropriate choice for prediction based on the principle of minimum root mean square error

Summary

Introduction

Fused silica has been widely utilized in the fabrication of large laser facilities, such as inertial confinement fusion (ICF), due to its unique optical, mechanical and thermal properties [1,2]. Subsurface damage (SSD) including surface microcracks and scratches are typical precursors for laser induced damage [3,4,5,6]. In order to withstand the irradiation of high-power laser, it is necessary to avoid SSD as much as possible in the machining technologies for fused silica. Ultra-precision grinding, as an efficient and economical manufacturing technology for optical elements, is one of the important technologies for processing high-precision and high-quality fused silica [7,8,9,10,11,12]. The surface and subsurface of fused silica after ultra-precision grinding usually contains SSD. The investigation on the surface integrity and SSD of fused silica induced by ultraprecision grinding has great importance

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Discussion

Conclusion