Fundamentals of material-specific process damping on rounded and worn cutting edges

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Self-excited vibrations, so-called chatter vibrations, are often a limiting factor when the productivity of machining processes is increased. However, chatter vibrations can be suppressed by increasing the contact of the flank face with the material, since oscillation movements into the material are damped by the springback of the material. This effect is called process damping. A further method of avoiding chatter vibrations is the simulative prediction of suitable process parameters, in which chatter vibrations are avoided. However, taking the process damping effect into account within simulative models is associated with high inaccuracies. This is due to the fact that the existing process damping models do not adequately reflect the highly complex elastic-plastic deformation processes below the flank face. The damping force acting on the flank face is often modelled as the product of a constant process damping coefficient and the volume indented under the flank face. Some preliminary work shows that the process damping coefficient depends on the rounding of the cutting edge and the clearance angle. This can be attributed to thermal effects and the neglect of plastic deformations within the model. However, the exact relationship between tool geometry, the elastic-plastic material behaviour below the clearance and the process damping force is unknown. Therefore, the aim of the project is to obtain a fundamental understanding of the material- and geometry-dependent process damping on the basis of the elastic-plastic material behaviour during the flank-face contact. In order to achieve this goal, the contact conditions at the cutting edge for different cutting edge rounding and wear conditions are analysed in orthogonal cutting test by high-speed images and force measurements. Based on the experimental results a new process damping model will be developed, which will be implemented in a material removal simulation of the milling process to predict the dynamic tool behaviour.