Abstract: The reliability method was introduced into the prediction of modal coupling chatter in robotic milling. Firstly， the reliability model was established and the limit state equation was obtained. Secondly， the fourth-order moment method was used to calculate the reliability and sensitivity to analyze the influence of various parameters on the milling stability. Finally， an example was given based on the engineering background of robotic milling bone. The results showed that the two-degree-freedom stiffness， cutting force coefficient and feeding direction of the robot will affect the stability of the milling process. Within a certain range， increasing the stiffness in X divection，reducing the stiffness in Y direction， reducing the cutting force coefticient and choosing the feed divection resonably are helpful to avoiding modal coupling chatter. The system is more sensitive to the change of cutting force coefficients than to the stiffness in X and Y directions， and has more significant benefit influence on stability.

Key words: robotic milling, modal coupling chatter, reliability, sensitivity, fourth-order moment method