Machining vibrations, also called chatter, induced by the relative movements between the cutting tool and the workpiece is an inevitable phenomenon during metal cutting processes. It leads to irregular surface flaws that generally reduces the cutting accuracy, machining stability, and tool life. Whereas no mutual conclusion has been put forward as the main causes of chatter, weak stiffness property and low damping ratio are among the causes pointed out by different researchers, depending on the type of workpieces and tool holders. Therefore, to ensure high work quality as well as tool and workpiece safety, development of efficient cutter suppression techniques is highly desirable.
Among the available suppression strategies, active control, passive control, and cutting parameter tuning are the most used in overhang tool holders. For instance, cutting parameter tuning is based on the dynamic behavior of the machining systems induced by the effects of the process parameters, active chatter control depends on the use of smart actuators while the passive control strategies are mainly depended on improving the dynamic behaviors of the machining system using vibration absorbers. Alternatively, the use of composite damping structure has recently gained popularity in the research field. It enhances effective energy dissipation through the use of free layer damping and constrained layer damping materials. However, the latter is widely preferred for vibration elimination due to the additional shear deformation in the damping layer that increases the rate of vibration energy dissipation. Unfortunately, it has fixed dynamic behavior that affects its machining operations.
Recently, Shandong University researchers: Yang Liu (PhD candidate), Professor Zhanqiang Liu, Professor Qinghua Song and Dr. Bing Wang investigated the dynamic behavior of constrained layer damping tool holder structure taking into consideration the effects of the chatter frequency. In particular, they analyzed the effects of the dynamic behavior of the tool holder on the machining stability and especially during the turning operation process. They purposed to improve machining stability. The work is currently published in Journal of Materials Processing Technology.
Briefly, the authors commenced by investigating the mechanical properties of the viscoelastic materials to confirm that they indeed depend on the frequency and temperature. This was confirmed through testing of the frequency and modal parameters. Considering the viscoelastic properties, the effects of the chatter frequency on the dynamic behavior of the constrained layer damping tool holder was further investigated through analytical methods. To validate the machining stability and damping performance, they manufactured a constrained layer damping tool holder based on dimension simulation and performed various modal tests and cutting experiments.
The research team recorded an impressive damping ratio increase by 99% for the manufactured constrained layer damping tool holder. This was attributed to the decrease in the cutting forces and an increase in the cutter depth. For the turning operations, the chatter suppression ability varied at different spindle speed with respect to the variation in the chatter frequency. Additionally, a significant improvement in the machining stability with better damping performance was achieved. Therefore, the study provides vital information that will further improve the efforts to suppress machining vibration for efficient machining processes.
Liu, Y., Liu, Z., Song, Q., & Wang, B. (2019). Analysis and implementation of chatter frequency dependent constrained layer damping tool holder for stability improvement in turning process. Journal of Materials Processing Technology, 266, 687-695.Go To Journal of Materials Processing Technology