Study on Regenerative Chatter Vibration in Ball End Milling of Flexible Workpieces

This paper presents an analytical model to predict critical cutting conditions for regenerative chatter vibration in the ball end milling process with tool inclination. The ball end milling is an important precision machining process, which is used in production of impellers, screw propellers and turbine blades with free-form surfaces. As these thin structures are flexible, the regenerative chatter vibration often occurs and causes severe problems such as short tool life and deterioration of surface quality. When the flexible workpieces are machined, the chatter vibration may occur in the through-thickness direction of workpiece. The vibration changes removal cross-section of workpiece in the present cut and furthermore in the next cut. This change in the cross-section produces dynamic cutting force. When this dynamic cutting force excites the mechanical structure and grows up the previous vibration, this closed-loop instability leads to the regenerative chatter vibration. In the present research, an analytical model of the ball end milling process with the regenerative chatter vibration is developed with consideration of tool inclination, and it is applied to predict the stability limits at a tool inclination angle and varied spindle speeds. The developed analytical model is verified by cutting experiments, and it is expected that the present analytical model is useful to optimize the tool path and the cutting conditions for highly-efficient cutting.