Evolution of Strain State of a Rolled Aluminum Sheet in Multi-Pass Conventional Spinning

Abstract

This study clarified the strain state evolution of a cylindrical cup spun from a rolled aluminum sheet in 13 passes. Measurements of radial (ɛr), circumferential (ɛθ), and thickness (ɛt) directional strains as well as forming forces revealed that the strain state evolved as follows: the cup-wall exhibits ɛr < 0 and small |ɛθ| and |ɛt| in early passes and ɛr > 0, ɛθ < 0, and ɛt < 0 in later passes; meanwhile, the cup-edge exhibits ɛr > 0 and small |ɛθ| and |ɛt| in early passes and ɛr > 0, ɛθ < 0, and ɛt > 0 in later passes. The relationship between the strain states and the forming force is interpreted as follows. The normal direction forming force, which pushes into the workpiece in the thickness direction, primarily deforms the workpieces. The radial direction forming force, toward the edge along the workpiece configuration, facilitates elongation in the radial direction of the cup-wall and results in ɛr > 0 during spinning. By contrast, a small radial direction forming force or a forming force whose direction is inverse against the roller movement direction restrains to elongate the material in the radial direction and facilitates shrinkage, thereby resulting in ɛr < 0 in the cup-edge in early passes. Furthermore, the small or inverse directional force facilitates the accumulation of the material to the edge and results in ɛt > 0 in latter passes.