Chip wave phase difference analysis of robotic milling and chatter dominant mode research

Chatter is a key problem that restricts the quality and efficiency of robotic milling, and the modal characterization of the robotic milling system is an important factor that affects the chatter. Doppler vibration measurement experiment shows that the vibration mode of the robotic milling system changes significantly with different modal frequencies under the sweep frequency excitation. The low-frequency mode shape is mainly manifested as the vibration of the robotic structure, while the high-frequency vibration mode shape is mainly manifested as the vibration of the spindle-tool structure. Therefore, the dominant modes of chatter are different under diverse cutting parameters, and the chatter suppression strategies are also significantly different. In order to provide a theoretical basis for the targeted chatter suppression under different cutting parameters, this paper studies the influence law of the robotic structure modes and spindle-tool structure modes on the chatter in the robotic milling system and establishes the analytical method of the dominant mode for the chatter of the robotic milling system. 

Firstly, the vibration mode shape of the robotic milling system is measured by a Doppler laser vibrometer, then the type of chatter is determined. Based on the classification of chatter types, the dynamic model considering the chatter dominated by robot mode and spindle-tool mode is established. Then, based on the variation law of chip wave phase difference (CWPD), a chatter participation degree analysis (CPDA) method is proposed to analyze the dominant mode for the chatter. The accuracy of the CPDA method on judging the dominant mode for the chatter is verified through a robotic milling experiment. The analysis results show that the number of teeth, modal parameters, and spindle speed will affect the change of dominant mode for the chatter. Finally, based on the analysis of the CWPD, a rapid evaluation index called the modal influence factor (MIF) for chatter dominant mode is proposed. The MIF proposed in this paper can effectively realize the judgment of the dominant mode for the chatter and provide theoretical support for chatter-free machining of the robotic milling system.