Bending Guide
Springback Explained
Why a part that looked perfect at the bottom of the stroke opens up slightly once the punch lifts — and what to do about it.
Springback is the tendency of bent sheet metal to relax back slightly toward its original flat shape after the bending force is removed. It's not a defect or a mistake — it's simply how metal behaves — but it means the angle you set the punch to isn't the angle you get on the finished part unless you plan for it.
Why it happens
When sheet metal bends, the outer surface of the bend stretches and the inner surface compresses. Most of that deformation is plastic — permanent — but a thin band of material near the neutral axis (the layer that neither stretches nor compresses) stays within its elastic range. Once the punch retracts and the bending force disappears, that elastic portion tries to return to its original, unbent state. It can't fully undo the plastic deformation around it, but it pulls the whole bend open by a few degrees in the process. That small recovery is springback.
What makes springback worse
- Higher-strength materials. More elastic energy is stored during bending, so more of it releases afterward. Stainless steel and spring steel spring back noticeably more than mild steel.
- Larger bend radius. A gentler bend (relative to thickness) has proportionally more elastic recovery than a sharp one.
- Thinner material. Relative to a given bend radius, thinner sheet has a higher ratio of elastic to plastic deformation.
- Wider V-die. More room for the material to move before contacting the die means more springback, and it becomes harder to predict consistently.
- Air bending vs bottoming/coining. Air bending shows the most springback of the three methods; bottoming and especially coining suppress it substantially. See air bending vs bottoming vs coining.
Approximate springback compensation by material
These existing rule-of-thumb ranges describe angle opening after a nominal 90° air bend. They are approximate planning estimates, not grade-specific settings. Yield strength, temper, radius-to-thickness ratio and tooling can move results outside them.
| Material | Approximate angle recovery | Compensation approach |
|---|---|---|
| Mild steel (S235/S275) | 1–3° | Trial a small overbend and measure after unloading. |
| Stainless steel (304) | 4–6° | Trial additional overbend; keep batch and grain direction consistent. |
| Aluminium | 0.5–1.5° soft 1xxx/3xxx; 2–4° 5052/6061 | Confirm alloy and temper; avoid a radius below the supplier’s minimum. |
| Spring steel / high-strength alloys | 6° or more; no universal upper value | Establish compensation on a sample in the actual heat-treatment state. |
For example, a measured 3° recovery suggests trialling an 87° loaded angle for a 90° finished bend. Measure the unloaded part before adjusting the production programme.
How to bend spring steel
Spring steel is designed to recover elastically. In its hardened and tempered condition, its high yield strength relative to elastic modulus allows substantial recovery before permanent deformation. It can also crack when forced around a tight radius, so extra force alone is not a solution.
Check annealed versus hardened condition
Confirm the grade and heat-treatment state from the material certificate. Where the specified manufacturing route permits it, form annealed stock and then have it hardened and tempered to the required properties by a heat-treatment specialist. Allow for distortion during heat treatment. Hardened strip needs grade-specific bendability and minimum-radius guidance; some conditions are unsuitable for the required bend. Do not locally heat or soften a finished spring without an approved process, as this changes its properties.
Use a larger radius and controlled over-bending
Choose a larger inside radius in line with the supplier’s guidance to reduce cracking risk. A larger radius can increase springback, so trial controlled over-bending using tooling with sufficient angular clearance. Measure the angle after unloading, then adjust in small steps. Bottoming may reduce springback but raises loads and contact stresses; use it only where the material, machine and tooling supplier permit it. It does not make hardened strip safe to bend around an unsuitable radius.
- Trial a sample from the same batch and in the same condition as the part.
- Deburr cut edges and inspect the outside of each trial bend for cracks.
- Where the design permits, run the bend line across the rolling direction; confirm orientation with the material supplier.
- Record radius, V opening, orientation, loaded angle and unloaded angle for repeat jobs.
How to compensate for it
1. Overbending
The most common fix on a press brake: set the punch to travel slightly past the target angle, so the part relaxes back to the correct angle after release. If a part needs to finish at 90° and the material typically springs back 3°, the punch is programmed to hit around 87°. Modern CNC brakes with angle-measurement systems can adjust this automatically; manual setups rely on test bends and operator experience.
2. Bottoming or coining
Switching from air bending to bottoming or coining physically presses the material into the die shape, which suppresses springback directly rather than compensating for it after the fact — at the cost of significantly more tonnage.
3. Adjusting die selection
A narrower V-die (within reason, following the 8×T guidance) tends to produce more consistent, slightly lower springback than an oversized one, since there's less room for the material to move before the die controls it.
4. Test bends before production
Because springback depends on the specific coil, temper and batch of material as much as the nominal grade, a short test bend before a full run is the most reliable way to dial in the right overbend angle for that particular job.
Check your tonnage before adjusting the die
Changing V-die width to manage springback also changes the tonnage you need — check both together.
Frequently asked questions
What causes springback in sheet metal bending?
Bending stretches material past its elastic limit on the outside of the bend and compresses it on the inside, but a thin layer near the neutral axis stays elastic. When the punch retracts, that elastic layer tries to return to its original shape, pulling the bend angle slightly open.
Which materials spring back the most?
Higher-strength, lower-ductility materials spring back more. Stainless and spring steel typically show noticeably more springback than mild steel, and mild steel more than soft aluminium.
How do you compensate for springback?
The most common method is overbending — setting the punch to a slightly sharper angle than the target so the part relaxes to the correct angle. Bottoming or coining reduce springback directly by pressing the material into the die shape.
Does a bigger V-die make springback worse?
Generally yes — a wider die gives the material more room to move before contacting it, increasing springback and making it less predictable.
Can you bend hardened spring steel?
Only where the grade and temper permit the required bend radius. Confirm bendability with the supplier, use a generous radius and test a sample. Where the process allows, forming annealed stock before controlled hardening and tempering is preferable.