What is springback in press brake bending?

Springback is the elastic recovery that occurs after the press brake load is released. The bend usually opens and its inside radius may increase, so the programmed forming angle must compensate for the measured recovery of the actual material and tooling setup.

What is the neutral axis in sheet metal bending?

The neutral axis is the layer through the bent thickness where longitudinal strain is approximately zero. Material outside it is in tension, material inside it is in compression, and its position is used to calculate bend allowance and flat length.

What does the K-factor represent?

The K-factor is the distance from the inside bend surface to the neutral axis divided by sheet thickness. It is a process-dependent input for bend allowance, not a universal material constant.

Does a larger V-die opening change springback and flat length?

Yes. A different V-opening changes the naturally formed inside radius, the contact geometry, required depth and often the released angle. That also changes the bend allowance or deduction used for the flat pattern.

Which bending method gives the least springback?

Coining generally suppresses springback more than bottom bending or air bending, but it requires far more force and purpose-matched tooling. Air bending is the most flexible method, so its springback is normally controlled through depth correction and measured setup data.

How should a shop establish a reliable bend allowance?

Start with a calculated value, then bend a representative coupon using the production material, punch, die opening and method. Measure the released part and store the approved allowance, deduction or correction with that exact setup.

COVO KNOWLEDGE

Press Brake Springback, K-Factor and Flat Length: A Practical Guide

Published: 2026-08-05

Learn how springback, neutral-axis position, K-factor, bend allowance and tooling choices work together to control press brake angles and flat length.

Press Brake Springback, K-Factor and Flat Length: A Practical Guide

Springback is the elastic recovery that opens a sheet-metal bend after the press brake load is removed. The neutral axis and K-factor describe how strain is distributed through the bend, while bend allowance converts that behavior into a usable flat length. These three ideas must be handled together if a shop wants repeatable angles and dimensions. This COVO engineering guide turns the core subjects of Chapter 4 in Sheet Metal Bending into a production workflow. It explains why a bend recovers, how air bending, bottom bending and coining change that recovery, where the neutral axis sits, how K-factor enters flat-pattern calculations and why a small error can multiply across a multi-bend profile. Springback reference: after the load is released, the bend angle opens and the inside radius increases. The source illustration has been enlarged and sharpened without changing its technical content. What causes springback? A bent sheet contains both permanent and recoverable strain. Fibres near the outside radius are stretched; fibres near the inside radius are compressed. Some of the deformation remains after unloading, but the portion that stayed within the material's elastic range tries to return toward its original shape. That elastic recovery produces the released angle and radius that the operator measures after the ram rises. Springback is therefore not one fixed number for a material name. It changes with yield strength, tensile strength, thickness, rolling direction, material condition, inside-radius-to-thickness ratio, V-die opening, punch radius, bending method and the consistency of the sheet lot. Higher-strength steels and many stainless grades normally require more compensation than mild steel. Aluminium behavior depends strongly on alloy and temper. The only dependable production value is the one verified with the actual material and tool combination. Direct answer: compensate springback by forming beyond the target angle, then measure the released part. Treat the calculated correction as a starting point and store the approved correction with the material grade, thickness, punch, V-opening and working length. Overbending: the normal air-bending correction Overbending means driving the workpiece to a slightly more acute angle than the target so elastic recovery brings it back to specification. For a nominal 90-degree part, the bottom-of-stroke angle m

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