Study on Surface Integrity of Precision Machined Brittle Materials
| Autor: | Wei-Haw Fan, 范偉華 |
|---|---|
| Rok vydání: | 2011 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 99 Brittle materials such as WC, SiC, Si, Al2O3, Zerodur and various optical glasses are difficult-to-machine materials for their high hardness and extreme brittleness. However, owing to their advanced optical, electronic and/or mechanical properties, demands for precision parts made of these brittle materials are increasing at a very fast rate. Advances in manufacturing processes are therefore important to the economic production of these parts. To ensure the quality of the generated surface and to improve the process efficiency, efforts have been made in this research to correlate the material properties, and machining processes/ conditions to the obtained surface integrity. Indentation and scratching tests were adopted in this study to gain fundamental understanding of the materials behavior, especially ductile to brittle transition, when subjecting to “cutting” operations. Both metal-bonded and resin-bonded diamond wheels were used in experiments of grinding WC and SiC specimens. Grinding parameters such as in-feed/cross-feed, cut depth and spindle speed were also studied. The results showed that, depending on the wheel and machining conditions, amorphous layer, dislocations, micro-cracks and fracture could be observed on the obtained surface. The grain size of WC and cobalt concentration also played important role in the achievable surface integrity. It is found that the critical cut depth of WC-C0%0 is around 2.5μm. The critical cut depth gets bigger as the cobalt concentration gets higher. The diffusion and depletion of cobalt induced by the elevated grinding temperature might result in the fracture mode changed from trans-grains to inter-grains and induce grain pull-out on the machined surface. SiC, having a relatively higher hardness and smaller critical cut depth, is much more difficult to be machined than WC for its surface/subsurface would be covered by scattered deep-penetrating median crack if any of the machining conditions goes beyond the ductile regime. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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