Dynamics identification and stability analysis in turning of slender workpieces with flexible boundary constraints

Abstract

The exact implementation of the turning stability analysis mainly depends on the realistic prediction model and reliable dynamical parameters. However, the workpiece located in the chuck-workpiece-tailstock dynamical system is generally regarded as a combination of a cantilever and a simply-supported beam. The effect of boundary conditions is ignored in the prediction of structural dynamics and stability limits. Hence, in this paper a model for slender workpieces with flexible boundary constraints is first built to improve the prediction accuracy of the turning stability. In this model, a two-dimensional (2D) compliance of the tool and part as well as the effect of the tool nose radius are incorporated in the dynamic force modeling, and the dynamical characteristic of slender workpieces in the chuck-workpiece-tailstock dynamical system is calculated according to the continuum theory. Then a novel strategy is proposed to identify the connection stiffness acting on the joint interface of the turning machine. According to the mathematical relation of workpiece dynamics induced by boundary conditions, a further theoretical derivation for the best selection of characteristic parameters, which is the critical part of the identification strategy, is developed on this basis. The optimal connection stiffness is determined by minimizing the deviation between the experimental and simulated values of characteristic parameters. The measured results of structural dynamics indicate that the connection stiffness identified from partial working conditions is also applicable to other working conditions. Finally, a series of turning experiments are conducted on this basis to verify the position-dependent stability limits considering flexible boundary constraints. The prediction result shows a good agreements with the experimental result. It proves that the proposed method has a unique advantage for the dynamics identification and stability analysis of the slender workpiece.