Investigation on chatter stability of robotic rotary ultrasonic milling

In recent years, industrial robots with higher flexibility and lower cost have become a hot topic in the manufacturing field. In terms of practical machining applications, they are mainly employed in the situations with low cutting forces such as deburring, chamfering and polishing. However, the weak stiffness of robot induces milling chatter easily. Severe chatter not only damages the dimensional accuracy of parts, but also decreases machining efficiency and tool life. Thus, it is urgent to seek a new method to suppress robotic milling chatter. In this paper, robotic rotary ultrasonic milling (RRUM) technology is used to restrict machining vibration. Meantime, an analytical model of stability is developed. Robotic milling system is considered as a three degrees of freedom (3-DOF) model. After that, based on analysis of dynamic chip thickness, a linear force model is developed through defining an angle γ affected by ultrasonic vibration. Then, the semi-discretization method (SDM) is applied to obtain stability lobe diagrams. The analysis result indicates that stability region of RRUM is improved by 133% compared with robotic conventional milling (RCM). Finally, verification experiments are carried out to prove the rationality and effectiveness of these stability lobe diagrams.