Change of Plastic Hinge Position in Radial Ring Rolling Without Guide-Roll

Radial ring rolling is an unsteady plastic deformation process. Internal stress of the ring is foundation of formation of the plastic hinge. The radial wall thickness of ring changes gradually along ring circumferential direction. Theoretical analysis and FE simulation show that: the plastic hinge is not always exactly opposite to the rolling deformation zone in ring rolling process without guide-roll. The plastic hinge position angle beta(0) is affected by ratio of rolling entrance wall thickness H-0 and rate of wall thickness change eta. Curve of beta(0)-H-0/eta is shaped as double pi staggered relative to each other. With the H-0/eta increasing, beta(0) reduces gradually and approaches to it in the range of H-0/eta>6.28. H-0/eta>14.6H(0)/R-2. Only when the rolling process is steady, and H-0 approximate to R-2, beta(0) is greater than pi, and approximates to pi. The beta(0) fluctuates dramatically when H-0/eta approximate to 5.71. In some cases, H-0/eta may fluctuate in 0 to 6.28, leading to the instability of plastic hinge position.