A Theoretical Basis for the Active Control of a Boring Bar Operation

Abstract

The properties of low stiffness and low structural damping in boring bars are widely known to be factors resulting in chatter and inaccurate machining. The application of active control offers a new alternative to improving the performance of a boring bar. This paper presents the theoretical basis for such an active control system. The analysis includes the practical consideration of principal modes in the boring bar model and discusses this influence on controller design. Simulation results using data from an experimental system illustrate some important factors of system design.

Exploring Once-Per-Revolution Audio Signal Variance as a Chatter Indicator

“…At a 2.79 mm axial depth for the same spindle speed, the chatter peak is just visible above the FFT noise floor, but the variance value does not suggest instability. 2 Aside from this data point, the once-perrevolution variance and FFT spectrum results demonstrate good agreement.…”

“…Chatter avoidance techniques are therefore an important area of machining research. Previous studies may generally be grouped into one of three categories: 1) mechanical changes to the machine tool structure and/or tool, e.g., tuned dynamic absorbers; [1][2][3][4][5] tools, holders, and spindles with increased dynamic stiffness; [6][7][8] draw bar force variation; [9] variable pitch cutters; [10][11][12][13][14] and tool overhang length adjustment to tune the tool point frequency response; [15][16][17][18][19][20] 2) intelligent selection of machining parameters, e.g., reduced regenerative chatter by appropriate spindle speed selection using stability lobe diagrams; [21,22] and 3) active control algorithms. [23][24][25] An equally important consideration, especially for situations of unmanned machining, [26] is the detection of chatter during milling (i.e., in-process detection).…”

Chatter control and stability analysis of a cantilever boring bar under regenerative cutting conditions

“…Active vibration control for boring bars was pioneered by Klein & Nachtigal (1975a;. They controlled the motions of the tool normal to the machined surface using feedforward control of the cutting force sensed from the torsional strain of the bar itself.…”