Passive and active strategies using embedded piezoelectric layers to improve the stability limit in turning/boring operations

Strategies for chatter modelling, monitoring and reduction are constantly under research, as chatter is well known for jeopardizing the industry productivity and the quality of machined parts. This research presents two different strategies to reduce chatter by improving the stability limit in turning/boring operations using piezoelectric layers embedded in the tool-holder. Both rely upon the fact that structural damping has a proportional relationship with the stability limit. Being so, the instability phenomenon can be significantly reduced by increasing the system's structural damping either passively or actively. In the proposed passive strategy, the piezoelectric layers are connected to a dissipative inductive-resistive shunt circuit. In the proposed active strategy, the piezoelectric layers are connected to a velocity feedback control scheme. The effectiveness of both strategies is evaluated by the comparison of numerical and experimental driving point Frequency Response Functions (FRFs) of the free end of the tool holder and experimental Stability Lobe Diagrams (SLDs). This numerical evaluation is performed using multiphysical finite element models and dedicated simulation schemes. The viability and robustness of both strategies are also experimentally examined by emulating different tool-holder's fixation conditions, which modify the system's dynamic characteristics. Operational experiments with both control strategies are also performed. It can be concluded that both strategies can be good alternatives for improving the stability limit in turning/boring operations, since they are capable of increasing the structural damping. Nevertheless, the proposed passive strategy lacks robustness since it requires the fine-tuning of the electrical components of the shunt circuit according to the system's dynamic characteristics. Finally, in spite of some technical difficulties, the proposed active strategy presents satisfactory performance and robustness for its practical implementation.