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Study of Chatter Stability in Boring Using Operating Deflection Shape

Mohammadi, Zohreh | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40394 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Movahhedy, Mohammad Reza
  7. Abstract:
  8. Chatter in machining systems is a limiting factor of workpiece surface, tool and machine life and material removal rate. Because of this, studying and modeling of vibrations is very important in the machining. This study is much importer in the boring operation because boring bar's length to diameter ratio is very high and so it is very sensitive to vibrations. As we know, vibration characteristics of a machine change between its operating condition and its resting mode. Because of this it's better to study machine's vibrations when it's working. This study requires some methods that can find operating parameters of machine. The aim of this work is to find these parameters. For finding these parameters and studying vibrations we use operating deflection shape (ODS) method. For comparing operating and stationary results in this paper we find vibration parameters of boring bar via some theoretical works and modal analysis method extra than operating deflections shape method and plot stability lobes of system using different method's parameters. Comparing the results show that natural frequencies found from theoretical works are very high relative to modal analysis and ODS method. This is because of modeling the boring bar as a cantilever beam in theory. The support of boring bar in real machining conditions is different from cantilever support and this is the reason of differences. For improving the results, some changes were done on the support for better modeling of its real conditions. After applying theses changes, natural frequencies found from theoretical works came nearer to modal analysis' results. Another result is that working natural frequencies found from ODS are upper than modal analysis' natural frequencies because of new boundary conditions. There are some differences between found stability lobes of three methods, especially in low spindle speeds, too. These differences that can be small or large in different machining conditions are because of some phenomena like process damping and ….
  9. Keywords:
  10. Vibration ; Modal Test ; Machine Tools ; Boring ; Operating Deflection Shape Method

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