Displacements analysis of self-excited vibrations in turning

TL;DR

This study analyzes the displacements caused by self-excited vibrations during turning, revealing the displacement plane, elliptical tool tip motion, and phase differences, with implications for understanding stability and stiffness in machining.

Contribution

It introduces an experimental protocol for displacement analysis in turning, linking vibrations to machine tool stiffness and dynamic behavior in a three-dimensional model.

Findings

Displacement plane attached to tool edge is inclined to machine axes.

Tool tip describes an ellipse, larger in unstable vibrations.

Phase difference observed between radial and cutting displacements.

Abstract

The actual research deals with determining by a new protocol the necessary parameters considering a three-dimensional model to simulate in a realistic way the turning process on machine tool. This paper is dedicated to the experimental displacements analysis of the block tool / block workpiece with self-excited vibrations. In connexion with turning process, the self-excited vibrations domain is obtained starting from spectra of two accelerometers. The existence of a displacements plane attached to the tool edge point is revealed. This plane proves to be inclined compared to the machines tool axes. We establish that the tool tip point describes an ellipse. This ellipse is very small and can be considered as a small straight line segment for the stable cutting process (without vibrations). In unstable mode (with vibrations) the ellipse of displacements is really more visible. A difference in phase occurs between the tool tip displacements on the radial direction and on the cutting one. The feed motion direction and the cutting one are almost in phase. The values of the long and small ellipse axes (and their ratio) shows that these sizes are increasing with the feed rate value. The axis that goes through the stiffness center and the tool tip represents the maximum stiffness direction. The maximum (resp. minimum) stiffness axis of the tool is perpendicular to the large (resp. small) ellipse displacements axis. FFT analysis of the accelerometers signals allows to reach several important parameters and establish coherent correlations between tool tip displacements and the static - elastic characteristics of the machine tool components tested.