15 June 2018 The study of sub-surface damage of fused silica after ultrasonic assisted grinding process
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We propose 3-step fabrication procedures for aspheric surface with larger departure. First step is to generate a specific aspheric surface with SSD depth under 10μm. Next step is to remove SSD and to keep the aspheric form by using Zeeko polisher with higher MRR pad. Final step is to figure and finish the aspheric surface by using QED MRF machine. In this study, we focus on 1st step to investigate the residual depth of SSD after grinding process on fused silica. The abrasion (Aa) or grindability is one of mechanical properties of glass material. The evaluation method of abrasion or grindability is different between the manufacturers. In this study, we apply the specific grinding parameters with #400 and #800 cylindrical diamond wheel on Tongtai GT-630 5-axes machine center. The ultrasonic assisted module is combined with BBT 40 tool arbor. The specifications of the ultrasonic unit are 15 - 45 kHz in frequency range, 0.2-2.5 μm in amplitude, and 1,000 Watt in power. The cross-grinding configuration is used in this study, due to its advantages of non-sensitive cutting direction in Z-axis, high cutting capability with large tools, and low cutting force for generating large convex aspheric surface. Before inspecting the SSD of the samples, wedge polishing would be applied on the ground surface for each sample. In general, the micro cracks of SSD aren’t observed easily by optical microscope due to the micro cracks were stuffed by abrasives of slurry and removed powders of glass. Thus, the mixture solution with hydrofluoric acid (HF) and hydrochloric acid (HCl) in water is used to etch ground surface. After etching, the micro cracks of SSD can be measured by Keyence VK-9700 confocal microscope. The depth of SSD is calculated by length of SSD and wedge angle of the plane.
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Ching-Hsiang Kuo, Ching-Hsiang Kuo, Chien-Yao Huang, Chien-Yao Huang, Zong-Ru Yu, Zong-Ru Yu, Shyu-Cheng Shu, Shyu-Cheng Shu, Keng-Shou Chang, Keng-Shou Chang, } "The study of sub-surface damage of fused silica after ultrasonic assisted grinding process", Proc. SPIE 10692, Optical Fabrication, Testing, and Metrology VI, 106921D (15 June 2018); doi: 10.1117/12.2311911; https://doi.org/10.1117/12.2311911


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