Sheet Metal Bending, Stamping Tonnage & Die Clearance Calculator

Calculate CNC air bending force, V-die opening, minimum bend radius, and stamping press tonnage per DIN 6935 and VDI 3389 with 1-click RFQ transfer.

Engineering Estimation Notice: Calculations are based on industrial air bending mechanics (DIN 6935) and stamping shear equations (VDI 3389). Actual press tonnage and springback depend on grain direction, die radius, and batch tensile variance. Consult Filame engineering for tooling design.

1. Process, Alloy & Sheet Parameters

DIN 6935 / VDI 3389

1. Select Manufacturing Calculation Mode

CNC Air Bending (Press Brake) Tonnage, V-die opening, min bend radius & flange Stamping & Punching (Press / Laser) Cutting tonnage, stripping force & die clearance

3. Sheet Dimensions & Geometry

Sheet Thickness (t) 0.1 – 20 mm

Bending Length (L) max 3,000 mm

Bend Angle (α) 30° – 165° (90° standard reference)

4. V-Die Opening Ratio (V / t)

6 × t — Tight radius / Thin sheet 8 × t — Industrial standard 10 × t — Medium / Stainless plate 12 × t — Thick plate / Low tonnage

2. Calculated Engineering Outputs

Rm: 400 MPa

Required Press Force (with 15% safety margin)

—

DIN 6935

Recommended V-Die Opening (V)

—

Natural air-bend ri —

Min crack-free ri —

Min outer leg b_min —

Est. springback Δα —

✓ Filame Machine Park Compatibility

Sheet Metal & Press Engineering Guide

Engineering Principles of Air Bending (DIN 6935) & Stamping (VDI 3389)

Whether designing a precision folded bracket for CNC press brake forming or sizing a progressive strip layout for high-speed automatic stamping, accurately estimating press tonnage, die clearance, and minimum bend radii early in the CAD phase prevents tool overload and part cracking.

CNC Air Bending Mechanics & V-Die Selection

DIN 6935

In three-point air bending, the punch presses the metal sheet into a V-shaped lower die without coining the bottom of the groove. Because leverage increases with a wider V-opening, selecting the right ratio V/t balances required tonnage against minimum flange length (b_min):

Air Bending Force Formula

F = [ (1 + 4t / V) · Rm · t² · L ] / V

Bending force increases quadratically with sheet thickness t and linearly with tensile strength R_m.

Natural Inside Radius & Flange

r_i ≈ 0.16 · V | b_min ≈ 0.72 · V

In free air bending, the inside radius is governed primarily by the V-die width V rather than the punch tip radius.

Stamping Shear Tonnage & Die Clearance

VDI 3389

When blanking or piercing metal strip on mechanical presses or Bihler multislide machines, the punch shears the material along the total cut perimeter P. Proper punch-to-die clearance (c per side, typically 5% to 10% of sheet thickness t) minimizes edge burrs and reduces stripping forces.

Questions & Answers

01 How is CNC air bending tonnage calculated for press brakes ?

In industrial air bending (DIN 6935), the required bending force depends on the material's ultimate tensile strength (Rm), the square of the sheet thickness (t²), the bending length (L), and the V-die opening width (V). Using the standard empirical equation F = [1.42 · Rm · t² · L] / (1000 · V), doubling the sheet thickness quadruples the required press tonnage. Filame's industrial CNC bending department operates multi-axis Trumpf TruBend press brakes up to 230 metric tons and 3,000 mm bed length.

02 How do I choose the right V-die opening and minimum inside bend radius ?

For standard cold-rolled steel and austenitic stainless steels up to 6 mm thick, the industrial rule of thumb is a V-die opening of V = 8 × t. In air bending, the natural inside bend radius (ri) forms at approximately 16% of the V-die opening (ri ≈ 0.16 × V). To prevent outer-fiber micro-cracking on work-hardened alloys like spring steel or 1.4310 stainless steel, the inside radius must never fall below the alloy's minimum crack-free bend radius.

03 How do you calculate stamping and punching press tonnage (VDI 3389) ?

Stamping or blanking shear force is calculated as F = P × t × ks, where P is the total sheared perimeter (mm), t is the strip thickness (mm), and ks is the material's shear strength (typically 0.8 × Rm). Adding a 10% stripping force and a 15% press safety margin ensures reliable tool life across high-speed automatic progressive presses and single-stroke mechanical presses.

04 When should I choose 2D laser cutting over progressive die stamping ?

For prototypes, pre-series, and small-to-medium production batches, 2D fiber laser cutting and CNC punching eliminate dedicated blanking die investments and allow immediate geometry revisions. Once annual volumes reach tens of thousands to millions of units, progressive die stamping on Filame's 10 T to 320 T automatic presses delivers the lowest unit piece price.

05 What is Filame's maximum press tonnage for heavy stamping and deep drawing ?

Filame operates mechanical and high-speed automatic presses from 10 T to 320 T for strip thicknesses from 0.15 mm to 6.0 mm, alongside a specialized heavy hydraulic press department reaching up to 7,000 T and 3,000 mm bed length for large structural sheet metal components.

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