Statistical investigation of modal parameters of cutting tools in dry turning

It is very important that optimized cutting parameters be selected in controlling the quality required for surface finishes. Unfortunately, surface roughness does not depend solely on the feed rate, the tool nose radius and cutting speed; the surface can also be deteriorated by excessive tool vibrations, the built-up edge, the friction of the cut surface against the tool point, and the embedding of the particles of the materials being machined. Hence, the forces, which can be considered as the sum of steady, harmonic and random forces, act on the cutting tool and contribute to the modification of the dynamic response of the tool, by affecting its stiffness and damping. These stiffness and damping variations are attributable to parameters that cannot be easily predicted in practice (regenerative process, penetration rate, friction, variation in rake angle, cutting speed, etc.). Furthermore, the effects of cutting parameters, which also contribute to the variation in the tool's modal parameters, are more useful for controlling tool vibration. This study focuses on the collection and analysis of cutting-force, tool-vibration and tool-modal-parameter data generated by lathe dry turning of mild carbon steel samples at different speeds, feeds, depths of cut, tool nose radii, tool lengths and workpiece lengths. A full factorial experimental design (288 experiments) that takes into consideration the two-level interactions between the independent variables has been performed. This analysis investigated the effect of each cutting parameter on tool stiffness and damping, and yielded an empirical model for predicting the behavior of the tool stiffness variation. (C) 2003 Elsevier Ltd. All rights reserved.