Reduction in Barreling of Hollow Cylinder by Combination of Axial Compression and Circumferential Torsion in Upsetting with Conical Dies

To reduce barreling of hollow cylinder in upsetting, circumferential one-way torsion with twist/compression speed of 0–12°/mm was combined with axial compression in upsetting. Due to combination of compression and torsion, the plastic flow of the workpiece was enhanced in the outer radial direction on the die–workpiece interface. Barreling was reduced by combining compression and torsion with lower than 5°/mm, whereas hourglass deformation occurred by combining compression and torsion with higher than 6°/mm. The workpiece was successfully deformed without barreling and hourglass deformation (0.97 < fraction of diameters of height center/end face < 1.01) by interrupting the die rotation in upsetting with reduction in height of lower than 50%.