Milling chatter control based on asymmetric stiffness

Chatter is a kind of instability phenomenon occurred in the machining process. It not only reduces the quality of the workpieces, but also limits the improvement of productivity. In this work, an asymmetric stiffness (AS) control method is proposed for chatter control in the milling process. First of all, a two-degree-of-freedom dynamic model of the AS spindle-milling system is developed. Based on that, the milling stability of the AS spindle system is analyzed. It shows that only increasing the stiffness of the spindle system in the X direction can effectively improve the stability in up milling process. However, in down milling process, the result is opposite, which means the stability will be improved by increasing the stiffness of the spindle system only in the Y direction. The phenomena are then experimentally validated in both down milling and up milling processes by asymmetrically controlling the stiffness of the spindle in the X and Y directions. Finally, an asymmetric stiffness control based chatter control method is proposed and also verified through the milling experiments. The experiment results show that chatter is effectively controlled by the proposed asymmetric stiffness control method and the quality of the finished surface is significantly improved.