Springback
Springback, and why your bend angles move
You program 90°. The press brake hits 90°. The part comes out at 92°. Nothing is broken — the material is doing what materials do.
What is actually happening
Bending does two things at once. Part of the deformation is plastic — permanent, the bend you wanted. Part is elastic — temporary, stored as stress in the material.
When the punch lifts, the elastic part releases and the bend opens up. That recovery is springback. Every bend springs back. The only question is how much, and whether you compensated for it.
What drives it
Yield strength. Higher yield stores more elastic energy. This is why stainless fights you and annealed copper does not.
R/T ratio. A generous radius relative to thickness leaves more material in the elastic zone. Tight bends spring back less, because more of the section has been pushed properly past yield.
Thickness. Thicker material at the same radius bends harder and springs back less.
Grain direction. Bending along the rolling direction behaves differently from bending across it — same material, same coil.
Indicative springback by material
For a 90° air bend at a moderate R/T ratio.
| Material | Typical springback | Note |
|---|---|---|
| Mild steel (CR) | 1 – 3° | Predictable. The forgiving one. |
| Galvanised steel | 1 – 3° | As mild steel. Watch the coating on tight radii. |
| Stainless 304 / 316 | 3 – 6° | High yield, springs back hard. Expect to overbend. |
| Aluminium 5052 | 2 – 4° | Well behaved for an aluminium. |
| Aluminium 6061-T6 | 5 – 9° | High yield, low ductility. Springs back and cracks. |
| Copper / brass, annealed | 0.5 – 2° | Very little. Soft and obliging. |
How it gets handled
Overbend. Go past the target so it relaxes back to it. Simple, and how most air bending works in practice.
Bottoming or coining. More tonnage, more of the section yields, less recovery. Consistent, but hard on tooling.
Measure and correct. Bend a coupon, measure what you actually got, adjust. This beats any table including this one, because it accounts for your machine, your tooling and this specific coil.
The bit that connects to flat patterns
K-factor tells you how much material the bend consumes — it sets the flat length. Springback tells you what angle you end up at. You can have a perfect flat pattern and a part that is still 3° out.
Our bend allowance calculator handles the first. The second is a tooling and process question, and it is why that calculator tells you to bend a test coupon on anything that matters.
Why we care
Most design problems are handoff problems. A drawing specifying a 90° bend without acknowledging that the material will not give you 90° on its own is a drawing that assumes the shop will figure it out.
Usually they do. Sometimes they do it differently to how you assumed, and the assembly does not fit.