πŸ“ Bending & Forming Design

Sheet Metal Forming Calculator

Bend Allowance Β· Bend Deduction Β· Flat Length Β· Outside Setback Β· Material Weight

mm
mm
Soft Al: R β‰₯ T Β· Mild Steel: R β‰₯ 1.5T Β· Hard: R β‰₯ 2T
Β°
Acute < 90Β° Β· Right = 90Β° Β· Obtuse > 90Β°
Air 0.30 Soft 0.33 Med 0.38 Hard 0.42 Full 0.50
Soft Al: 0.30–0.33 Β· Mild Steel: 0.35–0.40 Β· SS: 0.40–0.45
Bend Allowance (BA)
-mm
Arc length along neutral axis
Bend Deduction (BD)
-
mm
Neutral Axis R
-
mm (R + KΓ—T)
OSS (per side)
-
mm
Springback β‰ˆ
-
Β° overbend
Live Formulas
BA - -
BD - -
OSS - -
Bend Summary
Angle-
R / T ratio-
K-Factor-
BD vs BA-
πŸ’‘

Design Tips

Best practices for accurate bend calculations

πŸ“

Bend Radius Rule

Always keep inside radius β‰₯ material thickness to prevent cracking or splitting.

πŸ”‘

K-Factor Selection

Use proper K-factor: 0.30 for air bending, 0.50 for coining. Affects BA accuracy significantly.

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Springback

Over-bend by ~2–3Β° on mild steel. Springback increases with higher R/T ratios.

βš™οΈ

Validate Flat Pattern

Always verify flat pattern on paper template before cutting sheet metal stock.

mm
mm
Β°
Air 0.30 Soft 0.33 Med 0.38 Hard 0.42 Full 0.50
mm
Measured from bend tangent line to part edge
mm
Flat / Developed Length
-mm
L1 + L2 βˆ’ BD
Bend Allowance (BA)
-
mm
Bend Deduction (BD)
-
mm
L1 + L2
-
mm (before bend)
Material Saved
-
mm (vs L1+L2)
Live Formulas
BA - -
BD - -
Flat - -
Flat Pattern Summary
L1 + L2-
Bend Deduction-
Flat Length-
Bend Arc (BA)-
mm
mm
Β°
Outside Setback is the distance from the bend tangent line to the apex (mold line intersection). Essential for locating part features relative to the bend.
Outside Setback (OSS)
-mm
OSS = (R + T) Γ— tan(A/2)
Total OSS (Γ—2)
-
mm (both sides)
R + T
-
mm (outside radius)
tan(A/2)
-
dimensionless
Mold Line Dist
-
mm from apex
Live Formula
OSS - -
Total - -
OSS Reference
90Β° bend at R=TOSS = 2T
Larger A β†’ OSS↑ increases
Use for-
OSS / (R+T)-
Apex / Mold line OSS OSS ← L1 leg β†’ ↑ L2 OSS = (R + T) Γ— tan(A/2) distance from bend tangent to apex used for mold line dimensioning
mm
mm
mm
pcs
-
kg / piece
-
g / piece
-
kg total
-
cmΒ³ volume
Surface Area
-
cmΒ²
Density Used
-
g/cmΒ³
Total Volume
-
cmΒ³ (all pcs)
Weight / mΒ²
-
kg/mΒ²
Formula
Weight (kg) L(mm) Γ— W(mm) Γ— T(mm) Γ— Density(g/cmΒ³) Γ· 1,000,000 -
Weight Summary
Dimensions-
Density-
Per Piece-
Quantity-
Total Weight-

Sheet Metal Forming Calculator: Bend Allowance & Flat Pattern Guide

Accurately calculating the flat pattern (developed length) in sheet metal bending is critical for tooling design and material saving. Bend Allowance, Bend Deduction and K-factor all depend on the bending process and material. This calculator uses SolidWorks, CATIA and AutoCAD standard formulas.

πŸ“‹ How to Use This Calculator

  1. Enter material type and thickness (mm).
  2. Specify bend radius (mm) and bend angle (degrees).
  3. Select bending method, Air bending, Soft/Medium/Hard/Full, K-factor is set automatically.
  4. Note the Bend Allowance (BA), Bend Deduction (BD), Flat Length and Outside Set Back (OSSB) results.

πŸ“ Formula & Working Principle

K-factor = t_neutral/t (neutral axis location). Bend Allowance BA = (Ο€/180) Γ— (R + KΓ—t) Γ— ΞΈ. Bend Deduction BD = 2Γ—(R+t)Γ—tan(ΞΈ/2) βˆ’ BA. Flat Length = Sum of flat portions + Sum of BA.

πŸ’‘ Worked Example

CRCA steel 2 mm, R=4 mm, ΞΈ=90Β°, Air bend K=0.33. BA = (Ο€/180)Γ—(4+0.33Γ—2)Γ—90 = 7.32 mm. Flat portions: 50 mm + 80 mm. Total flat length = 50+80+7.32 = 137.32 mm.

❓ Frequently Asked Questions (FAQ)

Q: What is K-factor and how do I decide its value?

K-factor defines the neutral axis position (0=inner surface, 0.5=centre). Air bend: 0.33–0.38. Bottoming: 0.38–0.42. Coining: 0.45–0.50. It also varies with material softness.

Q: What should the minimum bend radius be?

Minimum bend radius β‰ˆ 0.5t to 2t (depending on material). Aluminium: 0.5–1t, Mild Steel: 0.5–1.5t, Stainless: 1–2t, High Strength Steel: 2–4t. A smaller radius risks cracking.

Q: What is springback and how is it compensated?

Springback is the elastic recovery that opens the bend angle slightly after bending. Compensate by overbending 2–5Β° extra (material-specific). Bottoming/coining minimises springback.

Q: Which radius should be measured: inside or outside?

Always specify the inside bend radius (R) on drawings, it corresponds directly to the punch nose radius. Outside radius = Inside radius + material thickness.

Q: How do I export a flat pattern to DXF/CAD?

SolidWorks Sheet Metal β†’ Flat Pattern β†’ DXF export. CATIA: Generative Sheet Metal Design β†’ Unfolded View. AutoCAD: manually calculate flat length and draw.