Mandrel Bending

Mandrel bending forms tubes around a die with an internal mandrel to control ovality and wrinkling, enabling tight-radius, high-quality bends.

Overview

Mandrel bending (mandrel-assisted bending) is a tube-bending method where a mandrel supports the tube ID during the bend. That internal support reduces cross-section collapse, wrinkling, and wall thinning, so you can hold tighter radii and maintain flow area compared with non-mandrel methods.

Choose mandrel bending for parts with tight centerline radii, cosmetic requirements, or performance-sensitive ID geometry (fluid flow, exhaust backpressure, pressure drop). It’s common for thin-wall tubing, stainless, and aluminum where ovality control matters.

Tradeoffs: higher tooling cost and setup time (bend die, clamp, pressure die, wiper, mandrel), more process tuning, and higher sensitivity to material variability and weld seam orientation. Very short tangents, close bend spacing, or complex multi-plane parts may require custom tooling or CNC controls, and springback compensation is often needed to hit angle targets.

Common Materials

  • Stainless Steel 304
  • Stainless Steel 316L
  • Aluminum 6061
  • Carbon Steel 1018
  • Titanium Grade 2

Tolerances

±0.5° (bend angle), ±0.010–0.030 in (bend location), ovality often controlled per spec

Applications

  • Automotive exhaust tubing
  • Hydraulic tube assemblies
  • Roll cage and chassis tubing
  • Aerospace ducting
  • Handrails and architectural tube frames
  • Medical device frames

When to Choose Mandrel Bending

Mandrel bending fits tight-radius bends where you must control ovality, wrinkles, and ID restriction, especially on thin-wall tube. It’s a good match for production runs where repeatability matters and tooling cost can be amortized. Specify it when bend quality and cross-section consistency drive performance or appearance.

vs Rotary Draw Bending

Choose mandrel bending when you need rotary draw bend quality on tight radii but the tube is thin-wall or ovality limits are strict enough to require internal support. Mandrels and wipers help maintain ID/OD geometry and reduce wrinkling on difficult materials or small CLR-to-OD ratios.

vs Compression Bending

Choose mandrel bending when bend deformation, flattening, or cosmetic wrinkling is unacceptable. Compression bending is faster and cheaper for large radii and forgiving tolerances, but mandrel bending holds shape and flow area much better on tighter radii and thinner walls.

vs Roll Bending

Choose mandrel bending when you need discrete, accurate bends with short radii and defined tangent lengths. Roll bending is better for large-radius sweeps and coils, but it won’t match mandrel bending for tight CLR, bend-to-bend repeatability, or ovality control.

vs CNC Tube Bending

Choose mandrel bending when the key requirement is cross-section control, not just multi-plane positioning. Many CNC benders can run mandrel tooling; specify mandrel-assisted bends when ovality/wrinkling limits and tight CLR are the drivers, and use CNC capability to manage rotation and bend location repeatably.

vs Stretch Forming

Choose mandrel bending when you need tight radii or compact packaging with minimal tangent growth. Stretch forming excels at large, smooth radii with good surface quality but typically can’t achieve the same tight CLR and local bend definition as mandrel bending.

Design Considerations

  • Call out tube OD, wall thickness, material/temper, and seam orientation (ERW seam) to reduce bend variability and quoting risk
  • Specify centerline radius (CLR), bend angle, and tangent lengths; include allowable ovality and wall thinning if they matter
  • Avoid extremely short straight lengths at tube ends unless you confirm grip/clamp requirements with the shop
  • Keep bend-to-bend spacing realistic; close bends may need special tooling or intermediate straight lengths for die clearance
  • Use standard CLR tooling where possible; custom dies and mandrels drive lead time and cost
  • Plan for end finishing after bending (trim, notch, flare, bead) and leave extra length for cutback and distortion