Sheet Metal K-Factor Calculator

Inputs

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Use measured flat sample when you have outside leg lengths and flat blank length, or measured bend allowance when BA is already known.
Starter range used only for comparison. The measured coupon K-factor is the production value when the sample matches the job.
Degrees the flange turns from flat. A 90 degree bend is a right-angle bend.
°
Measured inside bend radius.
mm
Sheet thickness.
mm
Outside mold-line length of the first leg.
mm
Outside mold-line length of the second leg.
mm
Measured blank length for the one-bend coupon.
mm

Results

Default result
Edit inputs
K-factor(K)
0.33
Pass

K is in the common empirical range for many press-brake bends

Also computed

Bend allowance(BA)Pass5.749mm

Bend deduction(BD)4.251mm

Outside setback(OSSB)5mm

Neutral-axis offset(K*t)Pass0.6599mm

distance from inside surface to neutral axis

Neutral-axis radius(R_n)3.66mm

Flat length from outside legs(L_flat)95.75mm

matches measured flat sample if inputs are consistent

Sheet metal K-factor preview: K 0.330, bend allowance 5.75 millimetersK-factor back-solve previewNeutral axis position from measured bend allowance or flat sample.neutral axis arcK-factorK = 0.330offset = 0.66 mmR/t = 1.50BA 5.75 mm, BD 4.25 mm, OSSB 5.00 mm.
Method notes 4 notes
  • K = (BA/theta - R) / t, where theta is bend angle in radians.
  • For a measured flat sample, BD = outside leg A + outside leg B - measured flat length, then BA = 2*OSSB - BD.
  • Selected starter band: ductile copper air bend, K = 0.30-0.40. Use it as a first blank estimate only.
  • K-factor is empirical. Verify it with production material, grain direction, tooling, die opening and bend method before using it for repeat flat patterns.

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