精密磨削加工Zerodur之次表面微裂縫分析與研究

Subsurface Damage in Precision Grinding of Zerodur

陸怡妏(Yi-Wun Lu)

指導教授 ： 廖運炫

國立臺灣大學/工學院/機械工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.00286

摘要

Zerodur是一種是擁有極低的熱膨脹係數的玻璃陶瓷材料，常使用在光學零件及人造衛星之主反射鏡上。本研究目的為探討鑽石砂輪精密磨削Zerodur的特性，由磨削參數、砂輪條件進行討論，了解磨削所造成的次表面微裂縫之機制及影響，並由實驗結果印證理論推導中磨削參數及砂輪條件所造成的次表面破壞，預測加工後的最大次表面微裂縫深度。
研究結果顯示，降低切深或工件速度可有效減少次表面微裂縫，而增加砂輪切線速度亦可減少次表面微裂縫，但到一定速度以上時，因溫度升高，反而使得次表面微裂縫增大；砂輪的條件方面，金屬結合砂輪產生的次表面微裂縫略大於同條件下的樹脂結合砂輪，而砂輪磨粒粒度對次表面微裂縫有決定性的影響，當磨粒粒度越大，造成次表層微裂縫越深，其影響程度遠大於磨削參數中的切深、工件速度及砂輪切線速度。
本研究中當磨削條件為切深5μm、工件速度30mm/min、砂輪切線速度10m/s時，使用金屬砂輪#600的加工結果，最大次表面微裂縫為2.91μm，而若其他條件不變、工件速度改變為10mm/min時，可得更小的次表面微裂縫。本研究的結果與理論公式相符，可在一定磨削條件內使用裂縫長度模型來預測磨削後的最大次表面微裂縫深度，最大誤差為24 %。

關鍵字

磨削 ； Zerodur ； 次表面破壞 ； 裂縫 ； 模型

並列摘要

Zerodur is a glass-ceramic made by Schott AG. With its very low coefficient of expansion, it can be used to produce mirrors which retain acceptable figures in extremely cold environments such as satellite. The primary subject of this study is to reach the characteristics of subsurface damage (SSD) in diamond wheels precision grinding of Zerodur, and establish the model of SSD in Zerodur using different grinding parameters, e.g. depth of cut, speed, feed rate, and different grinding wheel conditions, e.g. grain size and wheel bond.
The research results about the grinding parameters show that to reduce the depth of cut or work speed would be effective in reducing SSD, and increase the wheel velocity can reduce SSD. However, above a certain wheel velocity, the SSD increases due to high temperature. The results about the wheel conditions show that the metal bond wheel induces slightly larger SSD than the resin bond wheel. Using wheel with larger abrasive size will cause deeper SSD. The abrasive sizes have a decisive impact on the SSD, which is much larger than the grinding parameters. Experiments on #600 metal wheel with the depth of cut 5μm, work speed of 30mm/min and wheel speed of 10 m/s, the subsurface micro-crack is 2.91μm. If all variables remain the same but with work speed of 10mm/min, it will achieve subsurface micro-crack less than 2.91μm.
The results of this study match the theoretical formula, and the empirical formula from curve fitting could predict the subsurface micro-crack depth after grinding within a certain grinding conditions in which the error is less than 24 %.

並列關鍵字

Grinding ； Zerodur ； Subsurface damage ； Crack ； Model

參考文獻

[1] T. Döhring, P. Hartmann, R. Jedamzik, A. Thomas and F. Lentes, "Properties of Zerodur® Mirror Blanks for Extremely Large Telescopes," Proceedings of SPIE, vol. 6148, pp. 61480G.1-61480G.8, 2006.

[2] H. F. Morian and R. Mackh, "Zerodur® for Lightweight Secondary/Tertiary Mirrors," Proceedings of SPIE, vol. 3352, pp. 140-150, 1998.

[3] Schott AG, “ZERODUR® – Zero Expansion Glass Ceramic,” 2012.

[4] M. J. Viens, "Fracture Toughness and Crack Growth of Zerodur," NASA Technical Memorandum - 4185, National Aeronautics and Space Administration, 1990.

[5] Carl Zeiss AG, "Fabrication Technologies for Large Optical Components at Carl Zeiss Jena GmbH," 2010.