KEVOS® MAKEOS · Fabrication
Tube Bending Wall Thinning
How much will the tube wall thin on the outside of this bend, and thicken on the inside?
Approximate outer wall thinning and inner wall thickening of a tube bent to a centreline radius, with the bend ratio and wall factor used to judge bendability.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Tube outside diameter | mm | Outside diameter of the tube. |
| Wall thickness | mm | Nominal wall thickness. |
| Centreline bend radius | mm | Centreline radius of the bend die. |
| Minimum wall required (0 = not set) | mm | Minimum wall thickness allowed after bending (from the pressure or strength calculation). |
Method and formulas
- Outer wall ≈ t × R ÷ (R + D/2); inner wall ≈ t × R ÷ (R − D/2) (constant volume along the arc).
- Thinning % = (t − outer) ÷ t.
- Bend ratio = R ÷ D; wall factor = D ÷ t.
- Example: a 50 × 2 mm tube on a 100 mm radius thins to about 1.6 mm (20%).
Limitations
- Simple geometric estimate; actual thinning depends on the process (rotary draw, mandrel, pressure die boost).
- Ovality and wrinkling are not predicted.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check tube wall after bending against a minimum thickness
- Choose a centreline radius
- Decide whether a mandrel is needed
Who it is for
- Fabrication supervisors
- Manufacturing engineers
- Estimators
What you get
- Outer wall thickness and thinning
- Inner wall thickness
- Bend ratio R/D and wall factor D/t
Interpreting the result
- Small bend ratios with large D/t usually need a mandrel and wiper die.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1382–1386. Topic reference; no source tables or recommended settings are reproduced.
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