What causes spring-back in sheet metal?

During bending, the outer fibres stretch and inner fibres compress. Part of that strain is elastic, so when the punch releases, the elastic portion recovers and the bend opens up. Higher-strength, lower-modulus metals recover more.

Why does aluminum spring back more than steel?

Spring-back scales with yield strength divided by elastic modulus. Aluminum 6061-T6 has a high yield strength but a modulus roughly one-third that of steel, so its elastic recovery is much larger for the same bend.

How does bend radius affect spring-back?

A larger inside-radius-to-thickness ratio means a thicker elastic core relative to the plastic zone, so more of the deformation recovers. Tight bends near the minimum radius spring back the least.

Is this exact enough for production tooling?

It is a sound first estimate from the elastic recovery equation, but friction, tooling wear, grain direction, and material lot variation all shift the result. Always confirm the over-bend on a test coupon before committing.

What units does the calculator use?

Yield strength and modulus are in MPa, radius and thickness in millimetres, and all angles in degrees. The final included angle is the angle of the finished part, such as 90 degrees for a right-angle bend.

Sheet Metal Spring-Back Angle Calculator

Air-bend a sheet to ninety degrees, release the punch, and the part opens several degrees wider — that elastic recovery is spring-back. This calculator estimates how much a bend will open and the die angle you must over-bend to so the finished part holds the angle you actually want.

How it works

The change in bend radius on release is estimated from the elastic recovery of the outer fibre, using a standard relation between the radius before and after springback:

x      = (Ri × Sy) / (E × t)
Ri/Rf  = 4·x³ − 3·x + 1

Here Ri is the inside bend radius, Sy the yield strength, E Young’s modulus, and t the thickness. The factor Ri/Rf (the spring-back factor Ks) is always less than one. Because the bend angle measured from flat scales inversely with radius, the part bent to a given angle relaxes to that angle times Ks. To finish on the target bend the die must over-bend to target / Ks, and the difference is the spring-back you compensate for.

Example and tips

Bending 1.5 mm of 6061-T6 aluminum on a 3 mm inside radius to a 90° final angle, the factor Ks lands near 0.97 and the bend opens roughly 3°, so the die is set a few degrees past 90. The same bend in mild steel springs back far less because steel’s modulus is nearly three times higher. Keep the radius-to-thickness ratio modest, account for grain direction, and always verify on a scrap coupon — the equation gives a starting point, not a guarantee.