Experimental investigation of process damping nonlinearity in machining chatter

Neglecting the damping generated at the tool/workpiece interface, known as process damping, leads to inaccurate prediction of limit of stability at low cutting speed. Linear and nonlinear models have been reported in the literature that account for process damping. Although linear models are easier to implement in predicting stability limits, yet they could lead to misinterpretation of the actual status of the cut. Nonlinear damping models, on the other hand, are difficult to implement for stability estimation analytically, yet they allow predicting “finite amplitude stability” from time domain simulations. This phenomenon of “finite amplitude stability” has been demonstrated in the literature using numerical simulations. The objective of this paper is to investigate that phenomenon experimentally. The presentation in this work is focused on un-interrupted cutting, in particular plunge turning, to avoid unduly complications associated with transient vibration. The experiments confirm that because of the nonlinearity of the process damping, the transition from fully stable to fully unstable cutting occurs gradually over a range of width of cut.