Chatter stability of robotic rotary ultrasonic countersinking

Abstract

In recent years, industrial robots have received extensive attention in manufacturing field due to their high flexibility and great workspace. However, the weak stiffness of industrial robots makes it extremely easy to arouse chatter, which affects machining quality inevitably and generates noise pollution in severe cases. Compared with drilling, the chatter mechanism of robotic countersinking is more complex. The external excitation changes with cutting width and depth in countersinking. This characteristic results in time-varying and nonlinearity of robotic countersinking dynamics. Thus, it is urgent to propose a new method of chatter suppression and provide an accurate stability analysis model. As a new special machining technology, rotary ultrasonic machining has been proved to improve robotic drilling and milling stability effectively. Based on this, robotic rotary ultrasonic countersinking (RRUC) is proposed to improve the robotic countersinking stability in this paper. A three-dimensional stability domain method of RRUC is established. First, the countersinking process was divided into ρ parts. The dynamic model of every unit was constructed based on ultrasonic function angle (γ) and dynamic chip area. Then, the stability region of RRUC is obtained based on the semi-discrete method (SDM). Compared with the robotic conventional countersinking (RCC), RRUC improves the stability by 27%. Finally, the correctness and effectiveness of the stability region model are proved by robotic ultrasonic countersinking experiments.