Analysis of Vibration Damping in Machine Tools

AbstractThe dynamic behavior of a machine tool structure directly influences key metal cutting performance like being able to quickly remove hard workpiece material during roughing or minimize unwanted oscillations during high speed movements in finishing. While structure conception is still funded on designer experience and inventiveness, Finite Element models are very effective in analyzing the conceived structure, allowing its optimization, in term of stiffness increase and/or mass reduction.While today FE models provide a satisfying description of structure distributed stiffness and inertia, machine damping is usually not represented or is approximated as a uniform viscous damping, with no precise reference to the actual dissipation phenomena occurring in the structure. The corresponding incertitude in the estimation of the overall dynamic behavior often strongly limits the possibility of delivering accurate absolute estimations of machine performance. In order to overcome this limitation, this work aims at adding key energy dissipation mechanisms into numerical structural models: the velocity loop of the axis position controller, the frictional forces acting on the axis kinematic chain and guide ways and a distributed modal damping. Experimental tests have been performed on a machine tool axis equipped with tunable roller plus plain friction guide ways. The proposed model shows how different components and phenomena contribute into increasing machine performance, in term of material removal capacity. Given that the resulting models are essentially non-linear, appropriate methodologies are also suggested to integrate the proposed analysis into the usual machine development design cycle