Ring Rolling

Ring rolling forms seamless forged rings by expanding a pierced preform between rollers, producing high-strength rings with good grain flow and efficient material use.

Overview

Ring rolling (ring forging) produces seamless rings by piercing a heated billet to create a donut-shaped preform, then radially expanding it between a driven roll and an idler roll. The process builds near-net OD/ID with excellent circumferential grain flow, high integrity, and lower scrap than machining a ring from plate or bar.

Choose ring rolling for medium-to-large diameter rings where strength, fatigue resistance, and soundness matter—bearings, flanges, and pressure-containing components. It scales well from prototypes to production when sizes repeat, but it’s not a good fit for non-axisymmetric geometry or fine features.

Tradeoffs: tolerances and surface finish typically require finish machining; lead time can be driven by material, heat treat, and ring-roll mill availability. Very thin walls, extreme height-to-thickness ratios, and tight concentricity/flatness requirements increase process risk and machining stock.

Common Materials

  • 4140
  • 4340
  • 316L
  • 17-4 PH
  • Inconel 718
  • Ti-6Al-4V

Tolerances

±0.030"

Applications

  • Slewing bearing rings
  • Wind turbine bearing rings
  • ASME pressure vessel flanges
  • Pipeline and valve rings
  • Gear blanks and ring gears
  • Aerospace engine cases (ring segments/blanks)

When to Choose Ring Rolling

Pick ring rolling for axisymmetric rings where you need high strength, good fatigue performance, and reliable internal quality at moderate to large diameters. It works best when the part can be supplied as a near-net ring blank with machining allowance for faces, grooves, and precision features. Repeating sizes and families of rings improve cost and lead time.

vs Open Die Forging

Choose ring rolling when the end geometry is a true ring and you want controlled OD/ID growth with continuous circumferential grain flow. It typically delivers better material utilization and more consistent ring geometry than breaking down and machining from an open-die forged block.

vs Closed Die Forging

Choose ring rolling for large diameters and low-to-medium quantities where closed-die tooling cost and press capacity become limiting. Ring rolling makes seamless rings without the high-cost dedicated dies used to net-form complex, non-axisymmetric shapes.

vs Cold Forging

Choose ring rolling when part size is large, material is high-strength, or the required deformation is too great for cold forming forces. Ring rolling at hot-working temperatures handles thicker sections and tougher alloys, accepting that finish machining is usually required.

vs Upset Forging

Choose ring rolling when you need a seamless ring rather than a thickened boss or short axisymmetric preform. Upset forging is effective for localized thickening, while ring rolling is optimized to expand OD/ID and control wall thickness around the circumference.

Design Considerations

  • Define the ring as a near-net blank plus explicit machining stock on OD, ID, and faces (call out stock allowances on the drawing).
  • Set realistic concentricity/flatness requirements for the forged blank; reserve tight GD&T for post-machined datums.
  • Avoid very thin walls and extreme height-to-thickness ratios without supplier review; specify minimum wall and maximum OD/ID ratio targets.
  • Specify grain flow or mechanical property directionality only when needed, and align test coupon requirements with ring orientation.
  • Call out heat treatment condition (e.g., normalized, quenched & tempered, solution aged) and any NDE needs (UT/PT) early for quoting.
  • Provide OD/ID/height range and target weight; ring mills quote faster with a size window and machining plan rather than a single nominal only.