Dynamic modelling and performance enhancement for robotic milling of conventionally manufactured and 3D printed metals

Abstract

Stability characteristics of robotic machining, especially robotic milling, have been widely discussed to enhance milling performances. As compared to Computerized Numerical Control machines which are usually used for machining, robotic milling has advantages in high dexterity and low cost. This project aims to investigate the stability and performance enhancement for robotic milling of both conventionally manufactured metals and 3D printed metals. Unlike conventionally manufactured metals, 3D printed metals have an inherent limitation of poor surface quality which makes post-processing techniques such as milling essential. Therefore, a research interest is to deliver stable robotic milling processes for 3D printed metals. In this work, a regenerative chatter theory is adopted to predict stability performance during robotic milling processes. Instability, i.e., occurrence of regenerative chatter, is captured to verify the accuracy of theoretical predictions. The first part of the work investigated the robotic milling stability of conventionally manufactured metals where 6061 Aluminium alloy was selected as the workpiece material. Milling stability predictions were generated for 6061 Aluminium at three selected robot configurations. Modal analysis was applied to the robot-spindle- tool assembly at all three robot configurations to obtain the structural dynamics of the investigated robotic milling system. Validating milling experiments were conducted at each robot configuration. It was verified that regenerative chatter theory could produce an accurate indicator of milling stability and enhance robotic milling performance. The second part of the work investigated the robotic milling stability of 3D printed metals where Inconel 625 was selected to be the workpiece material. Due to the unique layering technique of 3D printing process, modifications were proposed to the conventional regenerative chatter theory to obtain more accurate stability prediction. Furthermore, impact of milling directions of 3D printed metals was studied to suggest an ideal milling direction that results in better milling performances.