Stretch Forming

Stretch forming bends tubes or extrusions by gripping the ends and stretching over a form die, producing smooth, low-distortion large-radius curves.

Overview

Stretch forming (often called aircraft stretch forming) creates controlled bends by clamping the part’s ends, applying tension, and wrapping it over a solid form die. The tensile load keeps the tube stable through the bend, reducing wrinkling and ovality and producing very smooth, repeatable contours—especially for large radii and long parts.

Choose stretch forming for constant-radius sweeps, fairings, frames, and structural members where surface quality and minimal distortion matter more than tight end-position tolerances. The main tradeoffs are tooling (dedicated form blocks), setup time, and geometric limits: it’s not ideal for tight radii, short parts with little grip length, or designs needing multiple closely spaced bends. Expect good profile repeatability along the arc, but plan for springback and trim/finish allowances at the ends.

Common Materials

  • Aluminum 6061
  • Aluminum 2024
  • Aluminum 7075
  • Stainless Steel 304
  • Titanium Grade 2

Tolerances

±0.030"

Applications

  • Aircraft fuselage and fairing frames
  • Wing and tail ribs/contours from extrusions
  • Seat tracks and cabin structural members
  • Curved stiffeners and longerons
  • Architectural curved rails and trim

When to Choose Stretch Forming

Stretch forming fits long parts that need smooth, large-radius curves with low ovality and good surface finish. It works best when the bend is a simple, continuous contour and you can dedicate tooling for repeat production or recurring programs. Plan on end trim and allow time for die development and springback tuning.

vs Mandrel Bending

Choose stretch forming when the bend radius is large and you want minimal tooling contact on the ID to reduce marking and distortion. It’s a good fit for long, smooth sweeps where mandrel setup is overkill and where slight end-length variation can be managed with trim.

vs Rotary Draw Bending

Choose stretch forming for large-radius, fairing-like contours and long parts where rotary draw would require large, expensive tooling and still risk wrinkling without heavy support tooling. Rotary draw is typically better for tight radii and precise bend location control; stretch forming favors smoothness over tight positional tolerance.

vs Compression Bending

Choose stretch forming when you need lower wrinkling risk and better control of ovality and surface quality on long arcs. Compression bending is faster and cheaper for loose requirements, but it tends to distort thin-wall sections and is less consistent on cosmetic or aerodynamic contours.

vs Roll Bending

Choose stretch forming when you need a controlled, die-defined contour with better repeatability and less trial-and-error tuning. Roll bending is flexible for prototyping and very large radii, but it can struggle to hold a precise profile over the full length without iterative adjustment.

vs CNC Tube Bending

Choose stretch forming when the geometry is essentially a long, constant sweep and the priority is smooth contour and low distortion rather than multiple bends with tight spatial control. CNC tube bending excels at complex multi-bend parts with accurate bend placement; stretch forming excels at fair curves defined by a form block.

Design Considerations

  • Provide sufficient straight grip/trim length on both ends for clamps and post-form trimming
  • Specify the centerline radius and allowable springback window; tight profile tolerances may require iterative die compensation
  • Avoid tight radii relative to tube diameter and wall thickness; large radii form more reliably with less ovality
  • Call out acceptable cross-section distortion (ovality/flattening) and surface marking limits for quoting
  • Keep the bend as a single continuous contour when possible; multiple closely spaced bends drive tooling complexity
  • Define orientation and datum scheme for inspection along the arc (profile template, CMM curve, or chord points)