Forming mechanism and characteristics of a process for equal-thickness in-plane ring roll-bending of a metal strip by twin conical rolls

• Published in: Journal of materials processing technology 2016-01, Vol.227, p.288-307
• Main Authors: Li, Hong-wei, Ren, Guang-yi, Li, Zhi-jun, Feng, Lu, Yang, He
• Format: Article
• Language: English
• Subjects: Conical roll; Deformation; Equal thickness; Forming; Forming mechanism; Friction; Metal strip; Metal strips; Roll gap; Roll-bending; Rolls; Strain; Strip
• ISSN: 0924-0136
• DOI: 10.1016/j.jmatprotec.2015.09.002

[Display omitted] •A process for equal-thickness in-plane ring roll-bending of a metal strip is presented.•Tangential velocity of the conical roll affects greatly ring formation.•The coupled influence of tangential velocity and deformation zone was found.•Positive and negative spread appears at the inner and outer half, respectively.•Adjustable parameters and small spread contribute to precise process control. A flexible and precise forming technology for low-cost, high-efficient and high-quality manufacture of equal-thickness rings is urgently required. To this end, a novel technique for equal-thickness in-plane ring roll-bending of a metal strip (ET-IRS) by twin conical rolls is presented. In this process, the twin conical rolls are placed to form an equal-thickness roll gap. The rolls rotate in opposite directions with identical angular velocity. The strip is bitten into the roll gap by frictional force and compressed equally across its width. Under the varying boundary conditions supported by the varying tangential velocity (VTV) of the rolls and varying deformation zone (VDZ) across the strip width, monotonically varying elongation of the strip is obtained, the coordination of which creates an equal-thickness ring. The results show that the VTV of the rolls plays a major part in ring formation, whereas the VDZ has little influence. However, remarkable coupling effects of VDZ with VTV exist. In comparison with the tangential velocity of the roll, the outlet velocity at the inner half of the strip is larger, but the velocity at the outer half is smaller. As a result, the inner half and the outer half experience frictional drag and traction, respectively, which produces a bending moment acting on the strip. The deformation characteristics of ET-IRS studied by simulation and experiment demonstrate that gradients exist in the radial and hoop strain components and outlet velocity of the strip across its width. Positive radial strain at the inner rim of the strip and negative strain at the outer rim result in positive and negative spread, respectively, leading to minimal resultant spread of the formed ring. The independently adjustable parameters, such as initial position of the strip z0, the roll gap t, the friction coefficient μ, the strip width b0 and the cone-apex angle α, affect the deformation. The gradient of radial strain increases with decreasing z0 and t and increasing μ and α, and the spread increases with increasing z0 and α and decreasing t and