Sheet Metal Flat Pattern
Flat length of a bent sheet-metal part. The neutral axis position is described by the K-factor; DIN 6935 derives it from the bend radius to thickness ratio.
Flat length76.16mm
- Bend allowance BA (neutral-axis arc)
- 4.16 mm
- Bend deduction BD = 2·OSSB − BA
- 3.84 mm
- Outside setback OSSB
- 4 mm
- K-factor used
- 0.325
- r / t ratio
- 1
- r/t = 1.00 — minimum inside radius for steel ≈ 1·t (material dependent)
METHOD
How it is calculated
BA = (π / 180) · A · (r + K · t) OSSB = (r + t) · tan(A / 2) L = a + b − 2 · OSSB + BA DIN 6935: k = 0.65 + 0.5 · log(r / t), K = k / 2
ASSUMPTIONS & NOTES
- a and b are outside dimensions to the intersection of the outer faces (virtual sharp).
- In air bending on a press brake the inside radius is about 15–16 % of the die V-opening.
- Confirm the K-factor with a test bend on your own machine.
Results are for preliminary design and checking; base the final design on the governing standard and safety factors.
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