Machining accuracy improvement and mode coupling chatter avoidance in robotic milling

Abstract

Robotic milling offers an attractive and cost-effective alternative to multi-axis CNC machining of large aerospace structures. Multiple degree-of-freedom (dof) articulated robotic arm-based machining has several potential advantages over traditional CNC machine tools including greater flexibility (reconfigurability) and lower cost. However, its industrial application is currently limited by its much lower stiffness and part feature dimensional accuracy compared to a CNC machine tool. Therefore, to achieve higher accuracy in robotic milling, the elastic deformation error due to its low stiffness must be adequately compensated. In addition, the low stiffness of articulated-arm robots gives rise to severe low frequency mode coupling chatter during machining. Previous studies have shown that such chatter can be suppressed by varying the tool feed direction to coincide with the direction of maximum stiffness of the robot. However, this approach limits the range of permissible robot motion and therefore its flexibility of use. This Thesis aims to advance current scientific understanding of the chatter phenomenon in robotic milling and to research a novel approach to address the limitations of the process for both elastic deformation compensation and chatter avoidance/suppression. It is expected that the proposed research will advance the underlying scientific understanding of the static and dynamic aspects of robotic milling. It is expected that the approaches for elastic deformation compensation and mode coupling chatter avoidance/suppression developed in this research will accelerate the application of robotic milling and thereby provide a highly flexible, low cost alternative for multi-axis milling of large aerospace structures.