The Directional Factor As A Key Determinant Of Chatter-Free Robotic Milling In Light Alloys

Robotic machining can be a cost-effective alternative to conventional CNC systems, especially for processing large or complex workpieces. However, the inherently low stiffness and posture-dependent dynamics of industrial robots results in them being highly susceptible to chatter, especially at low frequencies. Thus, this thesis focuses on the identification of low-frequency chatter in robotic milling, emphasizing the role of structural dynamics and the mean directional factor (MDF) in chatter formation. This is novel because there are some studies that attribute low-frequency chatter to mode-coupling in literature. To study the effect of MDF in a controlled environment, a custom flexure-based fixture was designed to mimic the dominant low-frequency mode typically observed in robotic arms. This fixture offers a single-mode-dominant system, which provides repeatable testing and clear interpretation of dynamic behaviour. Modal analysis was carried out using finite element modelling (FEM) and validated through experimental modal analysis (EMA). High correlation between simulation and test results confirmed the accuracy of the simplified model. The system was finally tested under machining conditions, validating theoretical predictions related to mean directional factors (MDF) and demonstrating that slotting operations can effectively reduce chatter. The results confirm that positive MDF values are associated with stable cutting, while negative MDF values lead to low-frequency self-excitation. This study offers a practical framework for enhancing stability in robotic milling and contributes to the development of chatter-resistant robotic systems for high-speed machining