When you bend sheet metal, the outer fibers stretch and the inner fibers compress. Part of that deformation is permanent (plastic) and part is elastic. Release the punch and the elastic part recovers — the bend opens to a larger angle and a larger radius. That recovery is springback, and it is unavoidable: every bend springs back to some degree.
Springback is the gap between the angle you form to and the angle you get. Controlling it means either forming past the target so it springs back onto nominal, or changing the process so less elastic energy is stored.
Three factors dominate. Higher material strength (higher yield strength) stores more elastic energy, so it springs back more — stainless and high-strength steels spring back noticeably more than mild steel. Larger bend radii spring back more than tight ones. And thinner stock, for a given radius, springs back more than thick.
Because high-strength materials and larger radii both increase it, the same tooling can land on-angle in one material and open up in another. The Springback Estimator helps anticipate the shift before you cut a test part.
In air bending, the simplest control is to overbend: form the part past the target angle by the expected springback amount so it relaxes back to nominal. A part that needs to finish at 90° might be formed to roughly 88° if it springs back about 2°.
Overbend amounts depend on material, thickness, radius, and die opening, so they are tuned, not looked up. This is also why air bending — which sets the angle by ram depth — is sensitive to material variation: a change in incoming material strength shifts the springback and therefore the angle.
Bottoming presses the material against the die at the bottom of the stroke, setting the angle largely by the die geometry and greatly reducing springback compared with air bending. Coining goes further: it applies enough pressure to plastically deform the material through its thickness at the bend, almost eliminating springback — at the cost of much higher tonnage (often several times the air-bend force).
The trade is force and tooling stress for consistency. Coining gives the most repeatable angle and tightest radius but demands a press and tooling that can take the load; bottoming is a middle ground. Air bending is the most flexible and lowest-force, with springback handled by overbend.
Match the method to the requirement: tight angle tolerance across variable material favors bottoming or coining; flexibility and low tonnage favor air bending with tuned overbend. Account for grain direction too — bends across the grain behave differently from bends along it.
No chart replaces a test bend. K-factor, springback, and overbend all calibrate best from your own sample bends in the actual material and tooling. The relationships here are standard; the exact numbers belong to your setup, so verify with tryout before running production.
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