Draft:Flowforming




Flow forming

Cold rotary metal forming process for thin-walled axisymmetric parts

Flow forming (also written flow-forming or flow turning) is a cold, rotary metal forming process used to manufacture thin-walled, high-strength axisymmetric components such as tubes, liners, pressure vessels, and wheel rims. During forming, one or more rollers locally deform a rotating preform over a mandrel, reducing wall thickness and elongating the part while reproducing the mandrel profile. The process is related to metal spinning and shear forming but is distinguished by substantial axial material flow and controlled wall-thickness reduction. [1][2][3]

Process

Flow forming typically starts with a thick-walled tube or cup-shaped preform mounted on a rotating mandrel. Rollers traverse axially while applying radial pressure, forcing plastic flow along the mandrel and producing near‑net‑shape parts with tight dimensional tolerances. Key variables—including reduction per pass, roller geometry, rotational speed, feed rate, and lubrication—govern thickness, elongation, residual stress, and surface finish. [1][3]

Variants

Commonly cited variants include:

  • Forward flow forming: material flows in the direction of roller travel.
  • Reverse (backward) flow forming: material flows opposite to roller travel.
  • Shear forming (closely related): primarily reduces wall thickness while maintaining or only slightly changing the starting diameter.[2][1]

Applications

Flow forming is used in aerospace and defense for cases and liners of rocket motors, pressure vessels, and engine components, where high specific strength and tight tolerances are required; and in the automotive sector for wheel rims and other lightweight structures. [3][4][5]

Advantages and limitations

Reported advantages include:

  • Improved mechanical properties from cold work and favorable grain flow.
  • Reduced weight via controlled thinning.
  • High dimensional accuracy and repeatability.
  • Lower material waste compared with machining or forging.

Limitations include:

  • Best suited to axisymmetric geometries.
  • Requires ductile alloys and precise process control.[6][1][3]

History

Modern flow forming matured in the mid-to-late twentieth century as spinning technologies and dedicated machine tools evolved; adoption accelerated with CNC control and improved process modeling. Industrial applications in aerospace and defense (e.g., rocket motor cases and liners) were established by the latter half of the twentieth century. [2] [7][3]

Relation to metal spinning

Trade literature and technical reviews distinguish flow forming from conventional metal spinning: spinning generally maintains wall thickness while forming sheet over a mandrel, whereas flow forming reduces wall thickness and induces substantial axial flow, often using dedicated equipment. [2][8]

See also

  • Metal spinning
  • Shear forming

References

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References

  1. Ray, G. “Flow Forming.” In ASM Handbook, Volume 14A: Metalworking—Bulk Forming. ASM International, 2005. https://dl.asminternational.org/handbooks/edited-volume/31/chapter-abstract/427357/Flow-Forming
  2. Wong, C. C.; Dean, T. A.; Lin, J. “A review of spinning, shear forming and flow forming processes.” International Journal of Machine Tools and Manufacture 43, no. 14 (2003): 1419–1435. doi:10.1016/S0890-6955(03)00172-X
  3. Podder, B. “Flow forming of thin-walled precision shells.” Sādhanā 43, no. 12 (2018): 208:1–208:14. https://www.ias.ac.in/public/Volumes/sadh/043/12/0208.pdf
  4. Hwang, S.Y.K. “Numerical Investigation of the Effect of Process Parameters on Flow-Formed Aluminium Wheels.” International Journal of Precision Engineering and Manufacturing 16, no. 10 (2015): 2153–2161.
  5. Altmann, P. “Experimental and Numerical Investigation of Rim Designs.” SAE Technical Paper 2022-01-0891 (2022). https://www.sae.org/publications/technical-papers/content/2022-01-0891/
  6. Hosford, W. F.; Caddell, R. M. Metal Forming: Mechanics and Metallurgy. 3rd ed. Cambridge University Press, 2007, pp. 230–233.
  7. Marini, D.; Cunningham, D.; Corney, J. “A review of flow forming processes and mechanisms.” In Key Engineering Materials, 651–653 (2015): 750–758. doi:10.4028/www.scientific.net/KEM.651-653.750
  8. The Fabricator. “Metal spinning 101.” (2009). https://www.thefabricator.com/thefabricator/article/bending/metal-spinning-101
  1. ^ a b c d Ray, G. (2005). "Flow Forming". Metalworking: Bulk Forming. pp. 516–521. doi:10.31399/asm.hb.v14a.a0004014. ISBN 978-1-62708-185-6.
  2. ^ a b c d Wong, C.C. (2003). "A review of spinning, shear forming and flow forming processes". International Journal of Machine Tools and Manufacture 43, No. 14 (2003). 43 (14).
  3. ^ a b c d e Podder, B (2018). "Flow forming of thin-walled precision shells" (PDF).
  4. ^ Hwang, S.Y.K. (2015). "Numerical Investigation of the Effect of Process Parameters on Flow-Formed Aluminium Wheels". International Journal of Precision Engineering and Manufacturing. 16 (10): 2153–2161.
  5. ^ Altmann, Peter; Herrmann, Stefan; Heinle, Konstantin; Ross, Frederick; Maihöfer, Martin; Waeschle, Alexander; Jehle-Graf, Erich; Schwarz, Volker (2022-03-29). Experimental and Numerical Investigation of Rim Aerodynamics (Report). Warrendale, PA: SAE Technical Paper.
  6. ^ Hosford, W.F. (207). "Metal Forming: Mechanics and Metallurgy". Metal Forming: Mechanics and Metallurgy. 3rd ed. Cambridge University Press. pp. 230–233.
  7. ^ Marini, Daniele; Cunningham, David; Corney, Jonathan (2015-07-10). "A Review of Flow Forming Processes and Mechanisms". Key Engineering Materials. 651–653: 750–758. doi:10.4028/www.scientific.net/KEM.651-653.750. ISSN 1662-9795.
  8. ^ "Metal spinning 101". 2009.