Optical glass fabrication technology 2: Relationship between surface roughness and subsurface damage

Ultrasonic vibration-assisted cutting (UVAC) has been regarded as a promising technology to machine difficult-to-machine materials such as tungsten carbide, optical glass, and hardened steel in order to achieve superfinished surfaces. To increase vibration stability to achieve optical surface quality of a workpiece, a high-frequency ultrasonic vibration-assisted cutting system with a vibration frequency of about 104 kHz is used to machine spherical optical steel moulds. A series of experiments are conducted to investigate the effect of machining parameters on the surface roughness of the workpiece including nominal cutting speed, feed rate, tool nose radius, vibration amplitude, and cutting geometry. This research takes into account the effects of the constantly changing contact point on the tool edge with the workpiece induced by the cutting geometry when machining a spherical steel mould. The surface morphology and surface roughness at different regions on the machined mould, with slope degrees (SDs) of 0°, 5°, 10°, and 15°, were measured and analysed. The experimental results show that the arithmetic roughness Sa of the workpiece increases gradually with increasing slope degree. By using optimised cutting parameters, a constant surface roughness Sa of 3 nm to 4 nm at different slope degrees was achieved by the applied high-frequency UVAC technique. This study provides guidance for ultra-precision machining of steel moulds with great variation in slope degree in the pursuit of optical quality on the whole surface.

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Evaluation of grinding-induced subsurface damage in optical glass BK7

Journal of Materials Processing Technology ◽

10.1016/j.jmatprotec.2015.11.003 ◽

2016 ◽

Vol 229 ◽

pp. 785-794 ◽

Cited By ~ 59

Author(s):

Hao Nan Li ◽

Tian Biao Yu ◽

Li Da Zhu ◽

Wan Shan Wang

Keyword(s):

Optical Glass ◽

Subsurface Damage

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Effect of Stress Wave between Adjacent Asperities Interaction on Subsurface Damage of Optical Glass in Precision Grinding

Materials ◽

10.3390/ma12081239 ◽

2019 ◽

Vol 12 (8) ◽

pp. 1239

Author(s):

Chen ◽

Ren ◽

Lin

Keyword(s):

Finite Element ◽

Optical Glass ◽

Diamond Particle ◽

Subsurface Damage ◽

Propagation Mechanism ◽

Analysis Model ◽

Precision Grinding ◽

Element Analysis ◽

Analysis Process ◽

Element Simulation

The interaction between adjacent asperities is a typical characteristic of the grinding process and plays an important role in the material removal mechanism. Therefore, in order to systematically investigate the formation mechanism of the subsurface damage, a precision grinding contact model between the diamond particle and optical glass with adjacent asperities is proposed in our research. The initiation and propagation mechanism of median/lateral cracks under residual stress, the propagation rules of the stress waves on the subsurface, and the interaction between the subsurface damage under stress superposition effect are fully investigated by a theoretical analysis and finite element simulation. The simulation results of the precision grinding model are verified by experiments, which show that the proposed numerical analysis model is reasonable and the finite element analysis process is feasible.

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Effect to the Surface Composition in Ultrasonic Vibration-Assisted Grinding of BK7 Optical Glass

Applied Sciences ◽

10.3390/app10020516 ◽

2020 ◽

Vol 10 (2) ◽

pp. 516 ◽

Cited By ~ 1

Author(s):

Pei Yi Zhao ◽

Ming Zhou ◽

Xian Li Liu ◽

Bin Jiang

Keyword(s):

Surface Roughness ◽

Ultrasonic Vibration ◽

Material Removal ◽

Surface Composition ◽

Rotation Speed ◽

Optical Glass ◽

Machined Surface ◽

Spindle Rotation ◽

Ultrasonic Vibration Assisted Grinding ◽

Ductile Removal

Because of the changes in cutting conditions and ultrasonic vibration status, the proportion of multiple material removal modes are of uncertainty and complexity in ultrasonic vibration-assisted grinding of optical glass. Knowledge of the effect of machined surface composition is the basis for better understanding the influence mechanisms of surface roughness, and also is the key to control the surface composition and surface quality. In the present work, 32 sets of experiments of ultrasonic vibration-assisted grinding of BK7 optical glass were carried out, the machined surface morphologies were observed, and the influence law of machining parameters on the proportion of different material removal was investigated. Based on the above research, the effect of surface composition was briefly summarized. The results indicated that the increasing of spindle rotation speed, the decreasing of feed rate and grinding depth can improve the proportion of ductile removal. The introduction of ultrasonic vibration can highly restrain the powdering removal, and increase the proportion of ductile removal. Grinding depth has a dominant positive effect on the surface roughness, whereas the spindle rotation speed and ultrasonic amplitude both have negative effect, which was caused by the reduction of brittle fracture removal.

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Influence of Abrasive on Planarization Grinding Based on the Cluster Magnetorheological Effect

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.325.542 ◽

2011 ◽

Vol 325 ◽

pp. 542-547

Author(s):

Qiu Sheng Yan ◽

Jie Wen Yan ◽

Jia Bin Lu ◽

Wei Qiang Gao ◽

Min Li

Keyword(s):

Surface Roughness ◽

Grain Size ◽

Optical Glass ◽

Removal Rate ◽

Mr Fluid ◽

Grinding Method ◽

Magnetorheological Effect ◽

The Difference ◽

Mr Effect

A new planarization grinding method based on the cluster magnetorheological (MR) effect is presented to grind optical glass in this paper. Some process experiments were conducted to reveal the influence of the species and granularity and content of the abrasive materials in the MR fluid on the machining effect, furthermore, the machining characteristic of grinded surface was studied. The results indicate that the abrasive influences definitively on machining effect of this planarization grinding method based on the cluster MR-effect. Under the certain experiment condition, with the content of the abrasive 10% and grain size 800# of SiC, best machining effect can be achieved. The difference species of abrasive results in various machining effects. As for the removal rate of K9 optical glass: abrasive CeO2 is the best, the Al2O3 is the second and the SiC is the worst. While the surface roughness: abrasive SiC is the lowest，the Al2O3 is the second and CeO2 is the highest.

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Laser-assisted grinding of reaction-bonded SiC

Journal of Micromanufacturing ◽

10.1177/2516598420965342 ◽

2020 ◽

Vol 3 (2) ◽

pp. 93-98

Author(s):

Xichun Luo ◽

Zhipeng Li ◽

Wenlong Chang ◽

Yukui Cai ◽

Jining Sun ◽

...

Keyword(s):

Surface Roughness ◽

Process Development ◽

Thermal Control ◽

Subsurface Damage ◽

Experimental Comparison ◽

Depth Of Cut ◽

Machined Surface ◽

Control Approach ◽

Damage Layer ◽

Conventional Grinding

The article presents the development of a novel laser-assisted grinding (LAG) process to reduce surface roughness and subsurface damage in grinding reaction-bonded silicon carbide (RB-SiC). A thermal control approach is proposed to facilitate the process development, in which a two-temperature model (TTM) is applied to control the required laser power to thermal softening of RB-SiC prior to the grinding operation without melting the workpiece or leaving undesirable microstructural alteration. Fourier’s law is adopted to obtain the thermal gradient for verification. An experimental comparison of conventional grinding and LAG shows significant reduction of machined surface roughness (37%–40%) and depth of subsurface damage layer (22%–50.6%) using the thermal control approach under the same grinding conditions. It also shows high specific grinding energy 1.5 times that in conventional grinding at the same depth of cut, which accounts for the reduction of subsurface damage as it provides enough energy to promote ductile-regime material removal.

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Experimental Investigation on Surface/Subsurface Damage in Rotary Ultrasonic Machining of Glass BK7

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.325-326.1357 ◽

2013 ◽

Vol 325-326 ◽

pp. 1357-1361 ◽

Cited By ~ 1

Author(s):

Yan Hua Huang ◽

Dong Xi Lv ◽

Yong Jian Tang ◽

Hong Xiang Wang ◽

Hai Jun Zhang

Keyword(s):

Surface Roughness ◽

Ultrasonic Vibration ◽

Process Parameters ◽

Subsurface Damage ◽

Spindle Speed ◽

Feed Speed ◽

Ultrasonic Machining ◽

Rotary Ultrasonic Machining ◽

Cutting Depth ◽

Influence Of Process Parameters

Experiments were carried out to study the effect of ultrasonic vibration on the surface roughness and subsurface damage (SSD) in rotary ultrasonic machining (RUM) of glass BK7. As a comparison, some conventional grinding (CG) experiments were also performed under the same process parameters with there of the RUM ones. The surface roughness of the RUM/CG samples was measured with a surface profilometer. The SSD of these specimens was assessed and characterized by a measuring microscope with the help of the taper polishing method. Also, the influence of process parameters (cutting depth, feed speed, and spindle speed) on the surface/subsurface quality was discussed. As a result, both the surface roughness and the SSD depth of the RUM/CG specimens were reduced with the increased spindle speed, while increased with the increasing of feed speed and cutting depth of the diamond tool. Compared with the CG process, the introduction of ultrasonic vibration resulted in the higher surface roughness and SSD depth, due to the fact that the max cutting depth of the abrasive in the RUM process increased by an amplitude compared with that in the CG process.

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