Performance of magnetorheological fluid based tunable frequency boring bar in chatter control

Low stiffness due to high slenderness ratio of the boring bar makes boring operation to be highly prone to machining instability. By providing increased stiffness and damping, the instability due to dynamic nature of the boring bar is successfully addressed in this paper. Maintaining the advantages of conventional viscous fluid damper, a provision to dynamically control the viscosity of the MR fluid is incorporated. Additionally, a rod is mounted as an inverse cantilever inside the primary structure of a specially designed boring bar. The rod vibrates within the MR fluid and the resistance to its movement is influenced by the viscosity of the MR fluid. The primary structure also experiences increased stiffness leading to change in natural frequency. From the dynamic characteristics obtained using impact and shaker excitation tests, stability lobe diagram (SLD) is constructed for a wide range of spindle speeds. For selected machining conditions, amplitude of vibration signals, roughness and roundness error are included in this paper and discussed further. For MR fluid filled condition with an input current of 3.5 A, amplitude of vibration is reduced by 29-44%, while surface roughness and roundness error are reduced by 14-59% and 5-41% respectively, thereby establishing the potential of MR fluid based tunable frequency boring bar for boring operation. (C) 2019 Elsevier Ltd. All rights reserved.