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Particulate morphology and deformation characteristics in modulation assisted machining
thesisposted on 06.05.2021, 01:48 by Indrani Biswas
Studies of mechanics and deformation in metal cutting operations have been largely limited to steady-state processes assuming constant forces and shear strain of cutting. However, ‘transient’ or varying deformation conditions are frequently encountered in manufacturing processes, when one or more processing parameters vary during the progress of the cut. Such conditions impose a lower overall strain on the resulting chip and affect the cutting forces and energies. In this study, the transient deformation characteristics are studied through the analysis of chip attributes (hardness and shape change) in a periodic cutting technique, Modulation Assisted Machining (MAM). In MAM, a sinusoidal modulation is superimposed on the tool feed, resulting in periodic engagement between the tool and workpiece. Deformation is confined to a specific volume of material and is also transient due to varying local conditions, manifesting an inhomogeneous and lower shear strain compared to steady-state cutting. A wide variety of deformation conditions from near steady-state to completely transient was achieved through the control of modulation frequency, which determines the contact length in each cutting cycle. Particles produced at lower frequencies exhibit increased hardness, consistent with the deformation more approaching steady state. Micro-indentation tests performed on each particle tracked the local variations in hardness along the length of cut, which agreed well with the non-uniform shape change observed on the cross-section of the particles. Microstructural examination of the chips made with and without modulation helped further describe the different deformation modes acting under periodic and continuous cutting conditions. MAM is also a valuable technique for metal powder processing. Individual chip particles are produced during each modulation cycle with controllable shape and size, and composition identical to that of the workpiece. Advantages of the process include a significant reduction in the specific energy of production, zero compositional variance and a tight distribution of particle sizes compared to atomization. Implications of scaling up the process for large-scale production and the possible applications of the metal particles made with MAM are highlighted.