Ph.D Student | Johny Saffury |
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Subject | Optimization of Non-Uniform Viscoelastic Turning Bars |

Department | Department of Mechanical Engineering |

Supervisor | Professor Emeritus Altus Eli |

Full Thesis text |

Chatter vibration of cutting tools is one of the main problems in machining, causing poor surface quality, short tool life and low productivity. Internal turning is a common cutting operation where the tool holder has large overhang ratio.

Tuned Dynamic Vibration Absorbers (DVA's) are passive devices widely used for chatter suppression.

The research motivation is to design a non-uniform viscoelastic tool holder with optimal chatter-resistance exhibiting higher chip removal rates and larger allowable overhang ratios. The dynamic stability limit of the holder is based on the linear theory of regenerative chatter which is the dominant mechanism in turning operations.

In chapter 2 a uniform Viscoelsatic Beam (VB) is compared to an elastic beam with local DVA. In contrast to the DVA tuning, the VB damping parameter is optimized by three types of criteria yielding the same damping value.

In chapter 3 an analytical solution of the Frequency Response Function (FRF) of general non-uniform elastic beam with attached DVA's is obtained by the Functional Perturbation Method (FPM). Optimized beam morphology for maximum chatter-resistance has been approximated analytically by the FPM solution. Material non-uniformity is constrained by a predetermined root mean square (RMS) value of morphology deviation. The optimized morphology is found to be approximately linear and far from the ‘‘intuitive’’ step-like one of Rivin and Kang (1992), and yields better chatter-resistance as the RMS is higher.

In chapter 4 an analytical solution of the FRF of non-uniform linear VB’s for non-separable classes is obtained by the FPM. Using the FPM solution, optimized beam morphology is obtained numerically. For heterogeneity in damping and mass density, constrained by the deviation RMS, the optimized morphology yields better chatter resistance when compared to the optimal uniform case.

In chapter 5 a new technique for vibration suppression of tool holders by specially designed cavities is developed, in which viscous fluid is forced to flow through narrow channels during service. The beam chatter-resistance is examined and optimized for different designs, and theoretical solutions are compared to experimental results.

In the last chapter the first eigen-frequency of non-uniform elastic beams is optimized numerically under inequality constraints. It was found that for bounded cross-section and modulus, multi-span three-step morphology is optimal.