The sudden appearance of a material bulge beneath the roller during tube spinning operation (referred to as “plastic instability”) is considered experimentally and examined quantitatively via an upper bound analysis. The phenomenon is explained by a sudden transfer of flow from one admissible mode to its competing mode when an external condition (or few conditions) is changed in a certain way to be discussed (e.g., increasing the roller angle of attack, increasing the initial tube thickness, etc.). As a by-product, the interrelation between the dominant variables of the process emerges. The associated formulation with its inherent idealizations enables one to mark the line between favorable and unfavorable working conditions of the spinning process. Experimental evidence demonstrates the utility of the proposed approach.

This content is only available via PDF.
You do not currently have access to this content.