UBC Theses and Dissertations
Parametric design of boring bars with adaptive tuned mass dampers van Zyl, David
Slender single point boring tools are highly sensitive to chatter vibrations and require additional chatter suppression design features to avoid unstable vibrations. Tuned mass dampers (TMDs) in boring tools are vibration absorbers where the natural frequency and damping ratio of the TMD is tuned to maximize the chatter resistance of the tool by increasing its dynamic stiffness. The chatter resistance of the tool is highly sensitive to the correct tuning of the TMD. A fixed TMD, where the TMD parameters are fixed upon installation, has intrinsic limitations in its use cases and effectiveness in suppressing chatter vibrations, namely due to suboptimal tuning, detuning, improper mounting, and the effects mounting the tool to a machine has on the dynamics of the structure. Adaptive TMDs, there the TMD parameters can be modified post-installation, address the limitations of fixed TMDs, however specialized modal analysis equipment and knowledgeable personnel are required in practical applications. This thesis investigates the implementation of a high-fidelity simulation model of the dynamics of a boring bar – TMD system developed to perform the tuning of adaptive TMDs digitally to address the barriers restricting the adoption of adaptive TMDs in industrial settings. The simulation model of the system consists of the frequency response function (FRF) of the boring bar calculated using finite element analysis (FEA) coupled with the analytical determined FRF of the TMD determining the dynamic behaviour of the combined system. A tuning algorithm is developed to determine the optimal damping ratio and natural frequency of the TMD according to the specific geometry of the boring bar and is compared against contemporary tuning methodologies. A boring bar – TMD system with a manual tuning attachment has been designed and fabricated and the tool tip FRF of the system has been measured. The digital model is verified by comparing the simulated subcomponent (TMD, and boring bar) vibrational parameters (effective mass, natural frequency, and damping ratio) against the subcomponent vibrational parameters identified from the measured FRF of the designed system.
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