Hydroforming

Hydroforming shapes tubular stock into complex, high-strength hollow geometries using internal high-pressure fluid and matched dies, ideal for lightweight structural parts at volume.

Overview

Hydroforming, or tube hydroforming, forms metal tubes into complex hollow shapes by pressurizing fluid inside a tube constrained in a die. The material expands to match the die cavity, creating smooth transitions, variable cross-sections, and tight corner radii without multiple welds or heavy machining. This process preserves wall thickness better than aggressive mechanical forming and delivers high structural stiffness-to-weight.

Hydroforming shines on medium to high volumes where tooling cost is amortized over many parts. Choose it for parts that must be strong, lightweight, and geometrically complex, such as multi-branch tubes, frames, or manifolds. Typical tradeoffs: higher upfront tooling and development, limited total expansion (often ~20–30%), and reliance on secondary operations for features like holes or precise ends. It is less suited for very low volumes, extremely tight dimensional requirements over long lengths, or very thick-wall material. When the geometry fits, hydroforming can replace multi-piece welded assemblies with a single part, improving consistency and reducing leak paths and assembly time.

Common Materials

  • Mild steel (1010/1020)
  • HSLA steel
  • Stainless steel 304
  • Aluminum 6061
  • Aluminum 6082
  • Copper

Tolerances

±0.010" to ±0.020" on formed tube profiles

Applications

  • Automotive engine cradles and space frames
  • Suspension and subframe crossmembers
  • Exhaust headers and manifolds
  • Bicycle and motorcycle frames
  • HVAC and refrigeration manifolds
  • Aerospace and rail structural tube sections

When to Choose Hydroforming

Use hydroforming for hollow structural parts where you want to replace multi-piece weldments with a single, complex tube shape and improve stiffness-to-weight. It fits best when you have moderate-to-high annual volumes, need smooth load paths, and can tolerate typical forming tolerances with secondary operations for critical features. It is especially effective when tube expansion and corner radii can be kept within standard forming limits.

vs Tube bending and welded assemblies

Choose hydroforming when the design currently requires multiple bent tubes and weldments to achieve complex 3D routing or branch connections. Hydroforming can combine those into a single leak-tight part, improving alignment, reducing weld distortion, and often cutting assembly cost at volume.

vs CNC machining from solid

Choose hydroforming when you need a hollow structural member, not a solid block, and wall thickness can remain close to the starting tube gauge. Hydroforming dramatically reduces material usage and cycle time compared to hogging out internal cavities, especially on longer parts or multi-branch geometries.

vs Metal casting

Choose hydroforming when you want high-strength wrought material properties and relatively thin, uniform walls instead of cast microstructure. Hydroforming is better for long tubular shapes and load-bearing frames where fatigue and crash performance matter, assuming the geometry can be built from tube stock.

vs Stamping and welded shells

Choose hydroforming when a closed section can be formed from a single tube instead of multiple stampings welded into a box or shell. Hydroforming reduces weld length and fixture complexity, and often yields better dimensional consistency and torsional stiffness.

vs Metal 3D printing

Choose hydroforming when the part is fundamentally a tube-based structure and production volumes justify hard tooling. Hydroforming offers far lower piece-part cost and faster throughput than additive, as long as you avoid extreme internal complexity that requires fully freeform shaping.

Design Considerations

  • Limit tube expansion and local thinning; aim for total perimeter growth in the 15–30% range unless your supplier validates higher
  • Use generous corner radii and smooth transitions to avoid splitting and heavy process tuning, especially in high-strength steels
  • Provide sufficient straight length at tube ends for sealing, gripping, and trimming in the hydroforming tools
  • Keep wall thickness as uniform as possible along the length; abrupt gauge changes or heavy end machining add cost and risk wrinkling
  • Call out realistic tolerances on formed sections and reserve tight tolerances for features added in secondary machining or piercing
  • Share forming simulations, crash/FEA load cases, and volume forecasts early so the supplier can optimize tube size, material, and tool concept