Press Brake Tonnage Chart: V-Die Opening, Material and Force

A press brake may be rated at 100 tons, 200 tons, or 500 tons—but the machine's rated tonnage alone does not tell you whether it can bend a particular sheet. If you have a drawing in front of you, the real question is usually much simpler: Can my press brake bend this material, at this thickness and bend length, with the tooling I have?

For air bending, the required force depends mainly on the material strength, sheet thickness, bend length, and V-die opening. Changing any of these parameters can significantly change the tonnage required.

For example, bending a 6 mm mild steel plate over 2 meters does not require the same force as bending 6 mm stainless steel over the same length. Similarly, changing the V-die opening affects both the required bending force and the resulting inside bend radius.

This guide explains how those factors work together. You will find a practical press brake tonnage chart, typical V-die opening recommendations, bend radius references, and a worked example showing how to estimate the required force before selecting or operating a press brake.

Where Does the Force in Air Bending Come From?

Air bending is the most common bending method used on a press brake. The punch pushes the sheet into the V-die, but the sheet does not fully contact the bottom of the die.

Air bending and bottom bending use different contact conditions and require different force estimates.

In air bending, the force comes from the press brake ram, which drives the punch downward against the sheet metal. The important point is that the force is not simply “pushing the sheet down.” The punch and V-die create a bending moment in the sheet.

Air-Bending Force Calculation

For a quick estimate of the force required for air bending, a commonly used calculation is:

P (kN) ≈ 650 × t² × L / V

Where:

P = required bending force, in kN

t = sheet thickness, in mm

L = bending length, in meters (not millimeters)

V = V-die opening, in mm

The coefficient 650 is a rounded estimate for mild steel with an ultimate tensile strength of about 450 MPa. In this version, t and V are in millimeters and L is in meters. If L is entered in millimeters, use 0.650 instead of 650. Do not mix the two unit conventions.

If the calculated force is given in kilonewtons, a quick conversion to metric tons is:

Required metric ton-force = P (kN) ÷ 9.80665

For example, 500 kN is about 51.0 metric ton-force. Dividing by 10 gives only a quick rounded estimate. Metric ton-force and US short ton-force are not interchangeable.

This formula is useful for preliminary press brake selection and job planning. However, the actual force can vary with the material grade, tensile strength, tooling geometry, bending method, and machine setup. For applications outside typical air bending conditions, the calculated value should therefore be checked against the machine manufacturer's specifications.

How to Read a Press Brake Tonnage Chart

Reference image supplied with the manuscript. Its force unit is not printed on the image; do not read its entries as metric tons. Use the explicitly labeled formula and calculated table below.

Calculated air-bending reference: 450 MPa mild steel, V = 8 × thickness, 1 m bend length. These are estimates in metric ton-force, not rated machine capacities.

Material Strength: Use the Actual Grade

How to Determine the Die Opening

The V-die opening is one of the most important tooling parameters in air bending. It affects the required bending force, inside bend radius, and the overall bending result.

For many ordinary mild-steel air-bending jobs, a V-opening around 6–8 times the sheet thickness is a starting point, not a universal setting. Thicker plate may need a larger opening. Check the tooling maker’s chart, minimum flange and the material’s minimum bend radius.

V ≈ 6–8 × t

Where:

V = V-die opening, mm

t = sheet thickness, mm

Example: 6 mm Mild Steel

An initial V-opening of 48 mm (8 × thickness) may be considered for a conventional air bend. Verify the required radius, flange length and tool load before using it.

Practical Suggestions

A narrower V-opening raises force and contact pressure and usually produces a smaller natural inside radius. It can increase marking or cracking risk. Springback depends on material and geometry and does not simply rise whenever the V-opening becomes smaller.

Do not choose a smaller V-opening just because the part requires high precision. Choose it to meet the bend geometry, then verify force, minimum flange and the tooling limits.

In air bending, the inside radius depends strongly on the V-opening and material, not only the punch nose radius. Around 0.16 × V is a common mild-steel estimate, not a universal rule. High-strength and wear-resistant grades need their manufacturer’s bending recommendations.

Worked Example: 4 mm Mild Steel over 3 m

Assume air bending, tensile strength 450 MPa, thickness t = 4 mm, bend length L = 3 m and V-opening V = 32 mm.

P = 650 × 4² × 3 / 32 = 975 kN

Required force ≈ 975 / 9.80665 = 99.4 metric ton-force.

A 100-ton machine would be close to this nominal estimate. That calculation alone is not approval to use it: check material variation, the manufacturer’s operating allowance, available force over the bend length and punch, die and holder load limits.

The shortcut P ≈ 8.3 × t × L (metric ton-force) follows only when V = 8 × t and the same 450 MPa mild-steel assumption applies. It is not valid for every V-opening or material.

For another material, an initial strength adjustment is P₂ ≈ P₁ × Rm₂ / 450, where Rm₂ is its actual tensile strength in MPa. For an illustrative 650 MPa material with the same geometry, the estimate is about 143.6 metric ton-force—not an automatic twofold multiplier or a machine recommendation.

Final Check: Is Your Press Brake Powerful Enough?

Selecting the right press brake is not simply a matter of choosing a machine with a higher tonnage rating. The required bending force depends on how the material, thickness, bend length, V-die opening and bending method work together.

For a typical air-bending application, the selection process can be summarized as:

Material → Thickness → V-die opening → Bend length → Required tonnage → Machine capacity

Start by identifying the material and its strength, then select an appropriate V-die opening based on the sheet thickness and required inside radius. From there, calculate the bending force and compare it with the actual capacity of the press brake.

Keep in mind that a tonnage chart provides an estimate. Tooling, load distribution, bend geometry, material variation and the bending method can all affect the actual force required. Applications involving bottoming or coining may require substantially more force than the values shown for air bending.

If you already know your material, thickness, bend length and V-die opening, use our Press Brake Tonnage Calculator for a quick estimate. If you are still deciding which machine fits your application, explore our press brake range or send us your material specifications and drawing. We can help you check the required tonnage and select a suitable machine and tooling configuration.

Use the press brake tonnage calculator to compare changes in thickness, bend length and V-opening. Treat the result as an estimate, not operating authorization.

For interface and load checks, review BEIGEMA’s press brake tooling options before specifying a machine and tool set.

Common Questions

Does a tonnage chart apply to bottoming or coining?

No. This chart and formula are for air bending. Bottoming and coining use different contact conditions and may require much more force; use the machine and tooling manufacturer’s approved data.

Can I apply full machine force to a short tool segment?

Not automatically. Check load per unit length, concentrated-load limits and all punch, die, holder and machine ratings.