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Sheet Metal & Forming
Interactive Calculator
Press Brake Tonnage & Bend Allowance Calculator
Calculate required air bending forming tonnage, recommended V-die openings, minimum flange dimensions, bend deductions, and flat pattern blank lengths for sheet metal press brakes.
Bending Geometry & Material Presets
Select an industrial forming profile or customize sheet parameters.
Material & Sheet Specifications
Standard cold-rolled or structural carbon steel with predictable springback and forming characteristics.
Die ratio: 8.0x thickness
Deflection: 90°
Flange Lengths (For Developed Flat Blank)
Applied K-Factor: 0.420
Required Press TonnageHeavy 250+ Ton Tandem Press
5497.9 t
53915.6 kN total force•12217.5 t/meter (4103.7 US tons/ft)
Min Flange Height (b_min):
8.4 mm
Est. Inside Radius (Ri):
2 mm
Flat Pattern Blank Calculations
Bend Allowance (BA):4.13 mm
Outside Setback (OSSB):3.5 mm
Bend Deduction (BD):2.87 mm
Developed Flat Blank:107.1 mm
Free Companion Template
Need to schedule your brake press jobs?
Download our free Sheet Metal Press Brake Scheduling Template (.xlsx) to group jobs by V-die opening and reduce tooling changeover downtime.
Download Press Brake Template (.xlsx)→Air Bending Tonnage Formula
Force (Tons) = (650 × T² × L) / V × Material Factor
In standard sheet metal fabrication, air bending relies on the opening width of the bottom V-die (V) and sheet thickness (T). Doubling the thickness quadruples the required bending force, while doubling the V-die opening cuts the tonnage in half.
- Mild Steel (CR4 / S275): Factor = 1.0 (Baseline 450 MPa UTS)
- Stainless Steel (304 / 316): Factor = 1.55 (Higher work-hardening)
- Aluminium (5052 / 6061): Factor = 0.50 (Ductile, lower tonnage)
K-Factor & Bend Deduction (BD)
Flat Blank = Flange 1 + Flange 2 - Bend Deduction
When sheet metal bends, the outer fibers stretch in tension while the inner fibers compress. The neutral axis (K-Factor) shifts inward, typically between 0.33 and 0.44 of sheet thickness.
Subtracting the calculated Bend Deduction (BD) from the sum of the external drawing dimensions gives the exact developed laser cutting or turret punch flat blank dimension.
Frequently Asked Questions
How is press brake bending tonnage calculated?
For standard air bending of mild carbon steel, tonnage is calculated using the formula: Force (Tons) = (650 * Thickness^2 * Length) / V-Die Opening. For stainless steel, multiply the resulting tonnage by 1.5 to 1.6 due to higher tensile strength (700 MPa). For aluminium, multiply by approximately 0.5.
What size V-die opening should I choose for sheet metal?
The standard rule of thumb for air bending mild steel (0.8mm to 6mm) is V = 8 * Sheet Thickness. For thin aluminium, a smaller opening of V = 6 * Thickness can be used for sharper inside radii. For heavy plate or high-strength steel (Strenx / Hardox), use V = 10 * to 12 * Thickness to reduce tonnage load and prevent cracking.
What is the difference between Bend Allowance and Bend Deduction?
Bend Allowance (BA) is the arc length along the neutral axis of the bend material. Bend Deduction (BD) is the amount subtracted from the sum of the two outside flange lengths to determine the flat blank pattern: Flat Length = Flange 1 + Flange 2 - BD. Bend deduction accounts for the material stretching and outside setback during bending.
What is the minimum flange length that can be bent safely?
The minimum flange height (b_min) required to span across the V-die shoulders without dropping into the die opening is approximately 0.7 * V-Die Width. Attempting to bend a flange shorter than 0.7V will cause the edge to slip into the V-groove, resulting in crooked bends and damaged tooling.