Vibrations in engineering and technology

Tryshyn Pavlo – Ph. D., Associate Professor of the Department of Mechanical Engineering Technology, National University “Zaporizhzhia Polytechnic”, Zaporizhzhia (69000, 64 Zhukovsky St., Zaporizhia, Ukraine, e-mail: trishin@zp.edu.ua), ORCID 0000-0002-3301-5124 

The paper considers the basic cutting conditions during turning under conditions of regenerative self-oscillations (SO). The physical foundations of the chip formation process under conditions of cutting following a vibration trace during turning are analyzed. The case is considered when the wave shift on the cutting surface on adjacent revolutions of the part is zero. In this case, according to the theory of regenerative SO, there is no fluctuation of the cut thickness and, as a result, there is no fluctuation of the chip formation force, which is a source of vibration support. The conditions of experimental turning of a part with a groove provided the same initial conditions at each revolution of the part when the cutting edge penetrates the surface of the part - the point of the beginning of the oscillations was constant, that is, there was no phase shift between the previous and current vibration trace on the cutting surface. Under these conditions, according to the theory of regenerative SO, vibrations should not be excited. At the same time, the obtained oscillograms clearly show that after the cutting there is a section in which the accompanying free oscillations are damped, then there is the section of the SO adjustment and the section of stable SO. When superimposing the oscillograms of several adjacent revolutions of the part, it is clear that there is no phase shift in the cutting section. The accompanying free oscillations when superimposing adjacent revolutions have almost the same shape. But starting from the SO adjustment section, it is visible that the oscillation period has a non-constant value, which leads to the appearance of a phase shift of a variable value. The results of the experiments showed that in the presence of waves on the cutting surface on adjacent revolutions of the part during turning, the real thickness of the cut is always variable and does not depend on the value of the phase shift. Thus, the erroneous statement that the phase shift between the vibration waves on the cutting surface of adjacent revolutions of the part provides excitation of vibrations has been refuted. Based on the results obtained, a physically correct picture of chip formation under the conditions of cutting along a vibration trace, when the longitudinal cross-section of the layer being cut is a wavy strip, has been formulated.

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