Sheet-metal development
Why bend allowance follows the neutral axis and why approved bend-test data controls production blanks.
ENGINEERING PRINCIPLE
Material on the inside and outside of a bend changes length differently; the neutral-axis length is used for preliminary development.
BA = θ(R + Kt)Variables and units
- θ in radians
- R and t in mm
- K from approved bend data
Worked example
At 90°, R = 3 mm, t = 2 mm and K = 0.33, BA = (π/2)(3 + 0.33 × 2) = 5.75 mm for that bend.
Calculation method
- Record every flange and bend in the intended production sequence.
- Use a K-factor supported by a bend test for the chosen material, radius and tooling.
- Add allowances or deductions consistently and validate the developed blank at the press brake.
Practical applications
- Brackets and enclosures
- Ductwork and panels
- Fabricated machine guards
Review boundary and reference
- Springback, reliefs and tooling affect production geometry.
- A generic K-factor never replaces a controlled shop trial.
Formula and displayed units independently checked for the stated conditions. This is not a code-compliance design method.
Source: J. G. Bralla, Handbook of Manufacturing Processes; verified bend-test data supersedes generic K-factor guidance.