A methodology to mitigate chatter through optimal viscoelastic absorber

Chatter is an undesirable dynamic instability phenomenon, mainly due to the low dynamic stiffness, that, in turning processes, results in poor surface quality and in a reduction in the cutting tool life. To overcome this problem, viscoelastic dynamic absorbers can be employed. Those absorbers are able to introduce reaction forces and dissipate vibration energy. In previous works, the main difficulty in the use of viscoelastic dynamic absorbers was in tool modelling uncertainties and in inaccurate viscoelastic material models. To overcome those difficulties, this article presents a new methodology to identify the machine tool structure dynamic properties by using 1-degree-of-freedom equivalent model combined with a fractional derivative model to describe the behaviour of the viscoelastic material. As a result, it was possible to design an optimal viscoelastic dynamic absorber for chatter mitigation in internal turning using non-linear optimization techniques. The use of generalized equivalent parameters for the absorber allows obtaining a simple equation of motion for the compound system (primary system plus absorber). The numerical and experimental tests were performed, showing the efficacy of the proposed controlling method design.