Mandrel Bending

Mandrel bending forms tight-radius, thin-wall tube bends with minimal ovality and wrinkling using an internal mandrel to support the tube during bending.

Overview

Mandrel bending is a tube and pipe forming process that uses an internal mandrel to support the tube ID during rotary draw bending. The mandrel controls ovality, reduces wall thinning, and prevents wrinkling, enabling tight radii and consistent cross-sections in thin-wall tubing. It’s common in applications where flow, fit-up, and appearance are critical.

Choose mandrel bending when you need tight bend radii (often down to 1–1.5× OD), controlled ovality, and repeatable geometry across many parts. It works well from prototypes through production, though dedicated tooling and setup time favor low-to-high volume runs of the same tube size. Tradeoffs include higher tooling cost than simple bending, limits on very large diameters or extremely thick walls, and the need for straight tangents for clamping and mandrel extraction. For most precision tube assemblies in automotive, aerospace, fluid handling, and structural frames, mandrel bending gives a strong balance of quality, cost, and throughput.

Common Materials

  • Aluminum 6061
  • Stainless steel 304
  • Carbon steel (mild)
  • Stainless steel 316
  • Titanium Grade 2
  • Copper

Tolerances

±0.010" to ±0.030" on bend location and leg lengths; bend angle ±0.25°; ovality typically <5–8% depending on size and wall

Applications

  • Automotive exhaust headers and downpipes
  • Roll cages and chassis tubing
  • Hydraulic and pneumatic hard lines
  • Aircraft fuel and brake lines
  • Furniture and medical equipment frames
  • Stainless process piping elbows and manifolds

When to Choose Mandrel Bending

Use mandrel bending when you need tight-radius, thin-wall, or cosmetic tube bends with low ovality and minimal wrinkling. It’s ideal for flow-critical lines, welded assemblies that must fit jigs or fixtures, and repeatable production of complex multi-plane tube shapes. Volumes from prototype to production are feasible, but the economics improve as repeat runs increase.

vs Rotary Draw Bending

Choose mandrel bending instead of bare rotary draw bending when the tube is thin-wall, the bend radius is tight, or cross-sectional distortion is a concern. The internal mandrel supports the ID, giving better ovality control, surface finish, and dimensional repeatability on demanding bends.

vs Compression Bending

Select mandrel bending over compression bending when you need higher precision, tighter radii, or better control of wrinkling and wall thinning. Compression bending is fine for simple, larger-radius bends, but mandrel assistance becomes critical when the tube must maintain a near-round ID or tight fit.

vs Roll Bending

Use mandrel bending instead of roll bending when you need discrete, tight bends rather than large sweeping curves. Mandrel bending holds geometry, angle, and cross-section much more accurately on compact bends, especially in assemblies where multiple legs must locate precisely.

vs CNC Tube Bending

Mandrel bending is often integrated into CNC tube benders; choose a mandrel-equipped setup when your CNC-bent tubes show unacceptable ovality or wrinkling. The mandrel adds internal support to the CNC-controlled motion, improving quality at the cost of more complex tooling and setup.

vs Stretch Forming

Choose mandrel bending over stretch forming for standard tube and pipe profiles where you need tight, localized bends and higher throughput. Stretch forming suits large, smooth curves in heavier sections or extrusions, whereas mandrel bending is more efficient for typical tubular assemblies and plumbing-style runs.

Design Considerations

  • Keep bend radius at or above the shop’s recommended minimum (often ≥1–1.5× OD for mandrel bending) to reduce tooling cost and scrap risk
  • Provide adequate straight tangents at tube ends and between bends for clamping, mandrel support, and extraction; short tangents drive custom tooling
  • Avoid holes, slots, or weld seams within at least 1–1.5× tube OD of the bend zone, or clearly flag them as critical so the shop can plan support
  • Specify which features are critical: angle, leg length, centerline radius, ovality, and clocking between bends; avoid over-tolerancing non-critical dimensions
  • Use consistent wall thickness and standard tube sizes; odd gauges or nonstandard OD/ID combinations increase mandrel and wiper die cost
  • Supply a 3D model of the full tube with centerline and material callouts so the bender can check feasibility, develop a flat length, and minimize trial parts