Tube hydroforming
Internal-pressure tube forming, stock and preform selection, pressure/feed coordination, wall distribution and finished-part qualification.
Tags: processes, shaping, tubes, forming
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Expanding a uniform tube from 50 to 60 mm mean diameter with 2.00 mm starting wall, fixed length and conserved metal volume gives 1.667 mm ideal wall, a 16.67% reduction. This simplified model excludes axial feed and local strain. Use measured or validated local thickness, especially at transitions and corners.
Schuler's high-pressure route seals the tube with end punches, forms with liquid pressure and feeds material axially before calibration. The die controls the outer contour. The inner contour depends on wall distribution. Schuler: internal high-pressure forming of tubes
This reference concerns tube forming with liquid pressure. Specify a different route explicitly when requesting sheet hydroforming or hot gas forming. A generic “hydroformed” label does not establish the starting stock, temperature, pressure sequence or delivered properties.
Define the complete route
A hydroforming operation may sit between bending/preforming and trimming, end finishing or other operations. Salzgitter Hydroforming lists bending, heat treatment, mechanical forming, hole operations, 3D laser cutting and washing among its available processes. Its presentation dated 10 May 2016 illustrates different chains for chassis and exhaust components. These are supplier examples, not a mandatory sequence for every part. Salzgitter: process chain, Hydroforming in Large-Scale Production, slides 1 and 8
| Input to the supplier | Why it matters |
|---|---|
| Final model, controlled dimensions and datums | Defines the delivered component rather than only a die cavity |
| Tube alloy, condition, dimensions and manufacturing route | Establishes the stock to be qualified |
| Bends, transitions, branches and end features | Identifies preforming, sealing and material-flow demands |
| Minimum walls and functional regions | Directs thickness evaluation and acceptance |
| Trimming, joining, coating and service requirements | Defines downstream effects and the final inspection state |
Specify the material and delivery condition alongside the process. Salzgitter's examples include carbon and stainless steels, aluminum and special metals, but the list establishes a range of applications rather than proving every grade/condition can form every contour. Select the particular tube with the producer and forming supplier. Salzgitter: material examples
Qualify the tube, not only the original sheet
WorldAutoSteel explains that tube manufacture introduces cold work and changes strength and available ductility. Subsequent bending, flaring and hydroforming must therefore use tube properties rather than simply transferring the incoming flat-sheet data. Its guidance also identifies the weld seam as a source of cross-sectional nonuniformity. WorldAutoSteel: tube forming
Record tube diameter, wall tolerance, ovality, seam characteristics, surface condition and any prior thermal or mechanical processing relevant to the approved route. Include the condition entering hydroforming after bending or annealing. A tube material certificate is necessary evidence where specified, but it does not by itself establish the remaining formability of every preformed region.
A concrete research example shows why preforming deserves separate attention. Mizumura and Kuriyama compared rotary draw and intrusion bending before hydroforming laser-welded interstitial-free steel tubes into an S-shaped part. The two bending routes produced different thickness distributions, forming windows and burst locations. The authors' favorable result for intrusion bending applies to the studied geometry, material and loading paths; it is not a universal replacement recommendation. Mizumura and Kuriyama, Materials Transactions 61 (2020), 515–521
Pressure, feed and friction form one system
WorldAutoSteel distinguishes expansion after die closure from pressure-sequence forming, where pressure supports the tube while the die closes and changes its section with limited circumference increase. End feeding can change the strain path and improve formability, but its influence is limited away from the ends. Thus specifying only peak pressure omits how material reaches the feature. WorldAutoSteel: hydroforming methods and end feeding
Specify the agreed pressure/feed sequence and preform, not a generic numerical recipe. In the Mizumura–Kuriyama study, burst, wrinkle, corner-filling and buckling limits were evaluated together. Raising pressure or increasing axial feed is consequently not a universal cure for an underfilled or thin region. Compare the location and stage of a defect with the approved process and incoming condition. Mizumura and Kuriyama, §2.4
Friction and lubrication also affect material movement. ASM's tube-hydroforming chapter identifies interface pressure, surface expansion/contraction and sliding velocity as important to friction, lubrication and wear, and discusses finite-element development of loading paths. Use representative inputs and verify the proposed process on physical parts; a simulation result alone is not an acceptance test. Ngaile, “Tube Hydroforming,” ASM International, 2012, pp. 179–209
A machine's clamping-force rating and fluid-pressure capability describe different equipment functions. Neither alone proves that a particular wall, radius, branch or seam can survive the complete operation. Request component-specific capability evidence rather than deriving feasibility from the largest advertised press.
Original idealized wall-balance example
Assume a straight circular tube segment with mean diameter 50 mm, uniform wall 2.00 mm, unchanged length and constant metal volume. Ignore axial feeding, local strain concentration, ends, bending, elasticity and material loss. The annular metal area is exactly π × mean diameter × wall thickness.
If its mean diameter becomes 60 mm while the wall remains ideally uniform:
- Initial metal area = π × 50 × 2 = 100π mm².
- Final uniform wall = 100 / 60 = 1.667 mm.
- Mean-circumference increase = 20%; calculated wall reduction = 16.67%.
A hypothetical 1.70 mm minimum would exceed this idealized uniform result by about 0.033 mm. This is not a prediction that a real component fails or passes: end feeding, axial strain and nonuniform geometry invalidate the simplified assumptions. It demonstrates why expanding a section cannot be assumed to preserve its original wall. Use measured or validated local thickness data for acceptance, especially at transitions and corners.
Delivery and acceptance
Define the inspection state after all required trimming, hole operations, end finishing and thermal processing. WorldAutoSteel notes that trimming AHSS requires appropriate support and tooling and that laser trimming can locally alter the edge condition. Do not treat the hydroformed contour as the only feature requiring qualification. WorldAutoSteel: trimming and design considerations
Separate external shape, minimum wall, seam integrity, surface defects, openings, cleanliness and functional performance. If leak or pressure testing is required, specify its method and acceptance basis independently; the pressure used during manufacturing does not automatically establish a service rating. Determine how inaccessible regions will be evaluated before freezing the geometry.
A useful handoff contains the controlled drawing/model, tube specification and traceability, preform and seam orientation requirements, approved forming and lubrication route, downstream operations, local wall requirements, inspection locations/methods and application-specific acceptance. Agree how material, tooling or sequence changes are qualified.
Source versions
Reviewed 2026-11-01. The Salzgitter presentation explicitly dates itself 10 May 2016. The research article's English edition was published 1 March 2020 (advance publication 20 January 2020); it identifies an earlier Japanese publication in 2019. ASM identifies the cited chapter as 2012. No separate technical issue date was verified for the live Schuler, Salzgitter or WorldAutoSteel pages. The volume-balance example and handoff recommendations are original.