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    Modelling of dynamic cutting force coefficients and chatter stability dependent on shear angle oscillation
    (Springer London Ltd, 2017) Turkes, Erol; Orak, Sezan; Neseli, Suleyman; Sahin, Mumin; Selvi, Selcuk
    Productivity of high-speed turning operations is limited by the onset of self-excited vibrations known as chatter. Unless avoided, chatter vibrations may cause large dynamic loads damaging the machine spindle, cutting tool or workpiece and leave a poor surface finish behind. Cutting force magnitude is proportional to the thickness of the chip removed from the workpiece. This paper presents a new procedure to determine dynamic cutting force coefficients (DCFC) required for process simulation by mechanistic modelling. In this study, a two degree of freedom complex dynamic model of turning with an orthogonal cutting system is considered. The complex dynamic system consists of a dynamic cutting system force model based on shear angle (phi) oscillations and penetration forces caused by the tool flank's contact with the wavy surface. The dynamic cutting force coefficients are identified by operating a series of cutting tests at the desired frequency, while changing phi oscillations and penetration forces. It is shown that the process damping coefficient increases as the tool is worn, which increases the chatter stability limit in cutting. The chatter stability of a dynamic cutting process is solved using the Nyquist law and time domain simulation (TDS) techniques and compared favourably against experimental results at low cutting speeds. Finally, comparisons among the proposed mechanistic model and experimental results show a good agreement with the analytically established SLD and, thus, validate the effectiveness of the proposed model.
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    Process damping model approach in milling operations
    (Springer Heidelberg, 2021) Orak, Sezan; Turkes, Erol; Selvi, Selcuk; Karabeyoglu, Sencer S.
    The subject of this study is a new Process Damping Model approach for milling with flat end milling cutter. Dynamic model of the cutting system was modeled and applied for the milling operation. The machining process is developed mathematically as a complex dynamic cutting model with two degree of freedom. This cutting model is designed according to both friction forces due to contact with wavy surface and shear angle (phi) oscillations. Considering Process Damping Ratios (PDRs), shearing force equations of the system are mathematically modeled. This created process damping model is a complex model, and it enables to obtain process damping values and rates both due to the deflection of the insert and the penetrating of the cutting edge to the wavy surface. It is also explained how the total process damping of the cutting system will change and how the equations will be arranged accordingly. Comparative process damping rates were obtained by making modal analyzes to obtain structural constants of different length cutting tools. The experimental results determined were applied to the developed model, and it was calculated that the rate of process damping varies depending on the factors. The most obvious difference that distinguishes this study from others is the change, and amount of the PDR is estimated by the analytical calculation procedure which runs in reverse to the conventional Stability Lobe Diagrams.