Stability of lateral vibration in robotic rotary ultrasonic drilling

Industrial robot is widely used to accomplish the drilling work in aviation industry due to its flexibility and relatively low cost. However, the low stiffness property of robot makes it easy to induce lateral vibration in the drilling process and restricts further improvement of drilling quality and efficiency. It is urgent to propose a new method for robotic drilling which is able to reduce the cutting force and suppress the lateral chatter effectively. In this study, robotic rotary ultrasonic drilling (RRUD) technology is proposed firstly. And the dynamic model to compute the stability lobe for RRUD is developed. The stability problem is simplified as a two degrees of freedom model. After that, the axial chip thickness is achieved on base of kinematic characteristics analysis. Furthermore, exponential method is applied to develop the dynamic cutting force model. Then, the stability lobe diagrams are obtained by frequency domain analysis. It is found that the stability region of RRUD gets a larger extension compared with robotic conventional drilling (RCD). Finally, pilot experiments are conducted and the results indicate that these stability lobe diagrams agree well with the experimental results.