Towards stable milling: Principle and application of active contact robotic milling

The low rigidity of industrial robots is a significant obstacle to high-performance robotic milling because it often leads to machining vibrations, which are undesirable. Typically studies on improving the stability of robotic milling rely on either maximising the stiffness of the robot in the direction of the milling force by optimising its configuration or reducing the milling force by using conservative milling parameters, which impose significant restrictions on the flexibility and productivity of the system. A new concept, called active contact robotic milling, is presented in this paper. It offers promise for use in robotic milling by ensuring system stability for the first time without sacrificing the flexibility and material removal rate. This is achieved by actively controlling the force between the robot and workpiece, that is, a force, in addition to milling force, is generated between the robot structure and workpiece. Theoretical analyses showed that the stability of robotic milling can be improved without requiring an elaborate robotic configuration or optimisation of the milling parameters. Therefore, flexibility and productivity of robotic milling are ensured. Based on the proposed principle, we develop a novel milling cutter that can control the contact force between the robot and workpiece. The experimental results confirm the validity of the proposed principle. The research findings presented in this study provide a concise and effective framework for a robotic milling system to avoid chatter in robotic milling. The proposed dynamic model is of great significance for understanding the influences of the interactions at the contact interface on system stability. Moreover, the proposed concept can inspire new tool designs for milling with flexible machine tool systems in the future.