Cutting Dynamics and Stability of Boring Bars

Abstract Boring bars with a high lengh-diameter ratio (L/D) tend to chatter. The limit of stability depends not only on the boring bar, its fixation and the machine tool, but also on the selected cutting conditions. A one dimensional model of the regenerative cutting is commonly used for simulation. However, this simple model is able to explain the influence of only a few parameters. Attempts to estimate the boundary of cutting stability by simulations with this model often give wrong results. Therefore, at our laboratory an approach to a more accurate cutting model was studied. Besides extension to three dimensions, the model considers the radius of curvature of the cutting tool corner. This allows the very important differentiation between roughing and finishing work. Modelling the thrust force as a infinite summation of infinitesimal forces perpendicular to the cutting edge, its direction can be calculated. Commonly the size of the forces is estimated by an exponential law depending on the thickness of the chip. Our tests showed that this assumption can be used in dynamics also, if the area of cut and the chip thickness are modelled exactly. This paper presents the new cutting model and illustrates its good accuracy in the estimation of the chatter stability when comparing experimental cutting test with simulation.