Robust Chatter Mitigation Control for Low Radial Immersion Machining Processes

Abstract

Chatter is a typical kind of unstable dynamics often encountered in machining processes, which often results in overcut and rapid tool wear. Hence, chatter phenomenon worsens the surface quality and reduces productivity in milling systems as well. Recent years have witnessed a surging industrial demand of high quality and high efficiency machining. Specifically, for low radial immersion milling situation, large depth of cuts is inevitably needed so as to increase the machining efficiency. To fulfill such a task, this paper develops a robust active control method to mitigate the chatter dynamics of low radial immersion milling processes. The present approach increases the axial depth of cuts, and the improvement is inversely proportional to the radial immersion ratio. Finally, case studies are conducted to show the substantially enlarged stable region in the stability lobe diagram (SLD) spanned by spindle rotational speed and axial depth of cut. Thus, the method can be expected to improve the efficiency of milling processes. Note to Practitioners —This paper seeks to mitigate machining chatters that worsen the workpiece surface quality in high-speed machining processes. To overcome such unexpected effects, traditional passive schemes simply adjust the rotational speed and cutting depth, which do not seek assistance from external power sources. Hence, neither the damping nor stiffness of the system can be changed, and a high maximal material removal rate (MMRR) is arduous to obtain. By contrast, this paper develops a robust active control method to mitigate the chatter dynamics for low radial immersion milling. In the design stage of the milling spindle, two active magnetic bearings (AMBs) are embedded in the tool house as control actuators, which produce extra force to counteract the chatters. In real milling processes, the chatters are detected by the associated inductive displacement sensors around the AMBs, and an uncertainty model is accordingly established with low radial immersion. With the detected vibration displacements, robust active control signals are calculated online, and then fed into the power amplifiers to drive the two AMBs. By this means, a closed-loop active control system is thus established for milling processes, which substantially enlarges the stable region of the SLD spanned by rotational speed and cutting depth. As a result, the proposed active control scheme can be expected to increase the MMRR and, hence, to enhance the productivity of milling processes.