University of Western Australia

Milind A. Siddhpura

[Truncated abstract] Chatter vibration has been researched for more than a century and it is still a major obstacle in achieving automation for most of the machining processes including turning, milling and drilling. Regenerative chatter is the most detrimental to any process as it creates excessive vibration between the tool and the workpiece, resulting in a poor surface finish, high-pitch noise and accelerated tool wear which in turn reduces machine tool life, reliability and safety of the machining operation. In this thesis, some of the chatter stability prediction and chatter detection techniques for the facing and turning processes are reviewed to summarize the status of current research in this field. Chatter stability prediction and chatter detection techniques are compared to find out the most suitable technique/s. After this rigorous review, one scope of research has been identified as establishing a theoretical relationship between chatter vibration and tool wear in order to predict tool wear and tool life in the presence of chatter vibration. After the review process, the thesis focuses on the stability of chatter vibrations and tool wear prediction by considering a single degree of freedom model of the orthogonal turning process. Chatter-free (stable) cutting parameters are obtained analytically for a sharp and a worn tool case respectively and stability lobes of an orthogonal turning operation are constructed using simulations. The effects of tool wear on chatter vibrations have been studied widely in the past, but the study of the effects of chatter vibration on tool life is very limited. Tool wear tests are usually mainly conducted under stable cutting conditions, which cannot explain the wear behaviour under vibratory cutting conditions. An attempt is made to predict the wear and life of a turning tool under chatter vibrations. A tool wear equation is derived which investigates the effects of self-excited chatter vibrations on tool wear in order to predict the tool life. This new tool wear equation clearly indicates that the tool wear increases very rapidly in the presence of chatter. The proposed analytical model and the tool wear equation have been validated with orthogonal turning experimental results. The thesis then focuses on the chatter stability prediction for a flexible toolworkpiece system in a turning process by considering a two degree of freedom model. The dynamic model of the turning process presented here considers two end-conditions of the flexible workpiece. Chatter-free (stable) cutting parameters are obtained analytically and stability lobe diagrams (SLDs) of a turning operation are constructed using simulations to distinguish between the stable and unstable regions. The SLDs are constructed for a variety of tool and workpiece parameters affecting the flexibility/compliance of the tool-workpiece system to investigate the effects of these parameters on the stability of the turning process. The proposed analytical model and its simulations have been validated through the turning experimental results. Overall, the proposed single degree of freedom and two degree of freedom analytical models of the facing and turning processes predicted the process stability accurately which are verified with the chatter experiments. A close agreement between analytical model predictions and experiments was observed...

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