Modelling and Simulation of Shear Bands and Tool-tip Vibration in Ultra-precision Diamond Turning

Single point diamond turning (SPDT) is an enabling technology in the category of ultra-precision machining with stringent achievable tolerances for the fabrication of precision components for optical, medical and telecommunication applications, etc., which require extremely high geometrical accuracies, in sub-micrometric form accuracy and nanometric surface finish. The development of single point diamond turning is attributed to the advancement of controls, feedback systems, servo drives, and general machine design and construction, etc. In SPDT, a monocrystal diamond cutting tool is used with a nanometric edge radius, form reproducibility and wear resistance. Different from conventional machining processes, the depth of cut in SPDT is in the order of a few micrometres or less. In this regard, the well-established classic theory of metal cutting for conventional and precision machining should be reviewed critically if it is applied in the study of the microcutting process in ultra-precision machining.;The theoretical and experimental study of this thesis has been divided into three parts. In the first part, serrated chip morphology with elastic strain induced shear band is studied in relation to its application in the generalised model for shear angle prediction. The second part is dedicated to a study of the physics of high frequency tool-tip vibration with its characteristic twin peak and influences on surface finish, with a proposed representative surface measurement method. With a dynamic model of the tool-work system, the third part reveals the connection between chip morphology and tool-tip vibration.;The originality and significance of this thesis can be identified by (i) its theoretical framework established for the analysis of the microcutting process in multiple aspects, taking into consideration chip morphology, machining dynamics and surface characterisation; (ii) instead of a computational method and pure theoretical models, the starting point of this thesis is experimental observation, for which the physical explanations are provided; (iii) apart from the theory for conventional machining, the proposed theory in this thesis originates from and is applicable to the ultra-precision machining process; (iv) the research includes not only the machine tools but also the factors of material properties.