Added Stability Lobes in Machining Processes That Exhibit Periodic Time Variation, Part 2: Experimental Validation

Abstract

Physical experimentation using a kinematically simple straight-edged orthogonal tube-end turning process both verifies the existence of added stability lobes as well as shows good agreement with the analytical solution and numerical simulations of Part 1. The experimental results also verify the added-lobe chatter frequency to be one-half the tooth frequency. Given validation of the analysis and simulation, they are then used to show the effects of variables not easily explored through experimental means, such as overlap factor, multi-tooth cutting, general periodicity and damping. The added-lobes are shown to exist with a zero overlap factor (i.e., no regeneration) and to scale in magnitude (limiting width of cut) relative to overlap factor. Furthermore, the added lobes are shown to exist for multi-tooth machining even when there are no periods of full cutter disengagement (i.e., no free vibration) as well as nonintermittent machining where periodic time variation exists for other reasons, such as spatially dependent stiffness. Finally, it is shown that damping primarily affects the bottom of the added lobes with minimal effect on the higher regions of the boundaries, indicating that structural damping becomes less important at ultrahigh speeds in cases for which the added lobes are the limitation.