In drills with helical chip flutes the coupling between axial and rotational degrees-of-freedom can cause chatter vibrations. These torsional-axial chatter vibrations can lead to a high frequency and unpleasant noise. It is desirable to design tools which are less prone to chatter vibrations and thus also makes less noise during operation. Dynamics of chatter vibrations in drilling is due to changes in chip-thickness that causes dynamic loads on the structure. These loads in return contribute and sustain vibrations. In this paper a simulation routine is proposed that can be used to model these chatter vibrations in drilling when damping of the drill-body is low. In case of low damping, the drill rotates backward in some instants. The importance of modeling of this phenomenon is emphasized in this paper and a method is proposed to model loads in case of backward rotations. The generated chip is calculated in each time-step and obtained chip-thickness is used to calculate dynamic loads. The structural responses are calculated in form of displacements by loading the drill with predicted dynamic loads based on the calculated chip thickness. Obtained displacements are used to calculate chip-thickness in the next time-step. Spectrum of simulated vibrations is compared with spectrum of measured noise and a good agreement between measurements and simulations is observed.
The work was done in Sandvik Coromant in cooperation with University West in Sweden. Funding of the project provided by Sandvik Coromant and KK foundation is gratefully acknowledged. Moreover, all supports from The Research School of Simulation and Control of Material affecting Processes (SiCoMaP) are highly appreciated.