Studies of Stability of Rotating Circular Cylindrical-Shaped Parts in Turning
| Autor: | Meng-Shu Tsai, 蔡孟書 |
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| Rok vydání: | 2016 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 104 The main goal of this thesis is to investigate the stability lobes of the circular cylindrical workpieces in turning. The workpiece is assumed to be made of isotropic material and is modeled as a rotating Timoshenko beam. The finite element equation of motion of a rotating shaft developed in Jan’s thesis [16] is adopted here to simulate the vibration of the rotating workpiece subjected to a spatial fixed regenerative cutting force. To predict the stability lobes of the turning of the circular cylindrical workpiece, in addition to using the finite element model solved with the direct integration Newmark-ß method, two simplified analytical models derived from modal equations are also considered. The difference between these two analytical models is that one includes the effect of gyroscopic matrix, while the other does not. Because the frequencies of the first two modes of rotating circular cylindrical workpieces are very close, to study the stability of turning of such a workpiece both modes have to be included in the aforementioned analytical models. The simplified analytical models are used to explore the influence on the stability lobes caused by considering or not the effect of the gyroscopic matrix and by using multiple modes in contrast to a single mode in the analytical model. Their results are also compared with those obtained from the finite element model using the direct integration method. Both rotating fixed-free and fixed-simply supported workpieces are being analyzed. It is shown that if the lowest two frequency modes of workpiece are considered, the stability lobes, for turning of workpieces having either type of boundary conditions, predicted by the analytical model which neglects the effect of the gyroscopic matrix look similar to those found by direct integration of the finite element model. The values of the lowest points of stability lobes obtained by these two approaches are very close, though phase differences exist between these two sets of stability lobes. When the second analytical model (which has included the gyroscopic effect) is used, it is found that in general the differences in phase stability lobes between the second analytical model and the finite element model decrease. However, the values of stability lobes predicted by the second analytical model and finite element model are found to have a great discrepancy. The cause of such results is still not clear and required further studying. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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