| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 102 === The demand in device made of brittle material increases dramatically and the piezo-electric material plays an important role in MEMS and Bio device. However, the low efficiency and quality of patterning the PZT material limit its applications in mass production product. Therefore, how to improve the patterning efficiency and quality is the key technology to extend the PZT material in various applications.
In this study, the cutting performance of PZT thin film deposited silicon wafer was analyzed with various feed rate and depth of cut. The effects of tool size and diamond thin film deposited on the micro mill were analyzed as well. Finally, the acoustic emission (AE) signal and cutting force collected during the cutting were analyzed for estimate their potential in monitoring bottom surface quality and cutting mode. In order to collect the data, experiments are conducted on a micro milling machine developed by the Precision Machinery Research & Development Center. The workpiece was made with Sol-gel process developed in the piezoelectric device and system Lab. in NCHU.
The results show that the cutting characteristics of PZT thin film is different from pure silicon. The ductile chip cannot be obtained for PZT thin film machining in this study and the more crack on the bottom of machined slot were observed as well. In machining PZT/Si wafer with depth of cut higher than the thickness of PZT thin film, the machining performance is also worse than the machining of pure silicon wafer. With the increase of the depth of cut, the cutting performance will be more close to the cutting of pure silicon. With the depth of cut lower than 2 um, the crack free bottom surface cannot be obtained and this result is more similar to the cutting of pure PZT thin film.
In considering the feed rate effect on the cutting performance, the brittle and ductile mode cutting can be observed with the reduction of feed rate. Moreover, with the continuous decrease of feed rate from ductile mode range, the ductile chip cannot be observed and instead the small particle can be detected around the cutting slot. For this feed rate range, the surface quality in the machined bottom will be worse than that with feed rate referring to the ductile mode cutting. However, the improvement of the bottom surface quality can be obtained with the feed rate reaching as low as 0.005um/rev. In the analysis of cutting performance for the PZT buck material, no ductile mode can be confirmed. However, for the feed rate set up in the 0.5mm tool test, the surface quality can be improved by decreasing the feed rate from 0.15μm/rev to 0.0003μm/rev, as well as to increase the feed rate from 0.15μm/rev to 1.5μm/rev.
For analyzing the tool size effect and the contribution from the nano-diamond thin film which is deposited on the tool, the diamond thin film can improve the tool life significantly. However, in the limited tool wear level, the bottom surface quality cut with tool without coating will be observed to be better than cut by the tool with diamond thin film deposit on tool. For the tool size effect, the size effect in machining can be observed to contribute more for the tool with the larger diameter.
Finally, for the analysis of AE and cutting force, the energy of AE signal was confirmed to increase as quality of machined bottom surface was deteriorated. By the way, the high frequency ripple on the cutting force can also be observed when the brittle cutting mode dominates the cutting behavior.
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