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Sheet Metal Springback and Overbend Calculator

After the punch lifts, elastic stress releases and the bend opens slightly. This calculator uses the classic pure-bending springback relation to estimate the final radius and the extra angle to program so the part lands on its target.

Your numbers

Inside bend radius under load

Material thickness

Yield strength

MPa

Typical: mild steel 250, stainless 304 about 290 annealed, aluminium 5052-H32 about 195.

Elastic modulus

MPa

Typical: steel about 205000, stainless about 193000, aluminium about 70000.

Target final bend angle (deflection)

deg

Your results

Tool angle to program

90.5307

Deflection angle to form so the part relaxes to the target.

Overbend needed

0.5307

Extra degrees beyond the target angle.

Relaxation parameter (Ri x Y / E t)

0.0024

Dimensionless group that drives springback.

Radius ratio Ri / Rf

0.9927

Pure bending relation. Values below 1 mean the radius grows after release.

Final inside radius

4.0295

Radius after springback, in mm.

The model assumes pure bending with a neutral axis at mid thickness. Real air bending springback also depends on die opening, tooling and material batch. Always confirm with a test bend.

Save results:

Overbend needed vs inside radius

Sweeps Inside bend radius under load from 1 to 20, holding your other inputs fixed.

Compensation history in your ERP

Interested in tracking bend compensation by lot and material? Share your setup flow. Optional.

Optional. The tool and every export work without this. No spam.

How to use it

Enter the bend radius, thickness, yield strength and elastic modulus for your material, then the angle you want after springback. The calculator gives the tool angle to program and the number of degrees of overbend. Higher strength, larger radius relative to thickness and lower modulus all raise springback. That is why aluminium and high strength steel need more compensation than mild steel at the same radius. Use the chart to see how quickly the overbend grows as the radius increases.

The relation used

The model uses Ri / Rf = 4 (Ri Y / E t)^3 - 3 (Ri Y / E t) + 1, where Ri is the radius under load and Rf is the final radius. The bend length on the neutral axis is assumed unchanged, so angle times (R + t/2) is conserved. Solving for the angle that relaxes to the target gives tool angle = target x (Rf + t/2) / (Ri + t/2). It is a textbook estimate for pure bending, a good starting point for programming and a useful sanity check.

Ri / Rf = 4x^3 - 3x + 1 with x = Ri Y / (E t)
Angle x (R + t/2) is held constant
Tool angle = target x (Rf + t/2) / (Ri + t/2)

Common mistakes

Do not use the radius you want after bending as Ri. Use the radius the tool forms under load. Do not rely on handbook yield values for coil you have not tested, since mill variation can shift springback by a degree or more. Press brake controls often include their own angle measurement and correction, so treat this tool as a planning estimate and log the final compensation used in your setup sheet for repeat jobs.

Frequently Asked Questions

Why does stainless spring back more than mild steel?

Stainless 304 has a higher yield strength at a similar modulus, so the elastic recovery is larger. Work hardening during forming adds to the effect.

Is the model valid for air bending?

It is derived for pure bending and is only an approximation for air bending, where the die opening also influences the result. Use it as a starting estimate and verify on a test part.

How many degrees of springback is typical?

Mild steel with a low radius to thickness ratio often shows well under a degree to about two degrees. Aluminium alloys and high strength steels can need several degrees. Always measure.

Can I enter inches and psi?

Yes, if you use consistent units. Radius and thickness must share one unit, and yield strength and modulus must share another pressure unit. The relation is dimensionless.

Setup sheets that record actual compensation by material and lot are valuable. We can help link that history to your ERP routing so programmers start from proven values.

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