Bend Force Calculator - Calculator Academy

Calculate bend force, k constant, bend length, tensile strength, thickness, or die opening from five known press brake bending values.

Bend Force Formula

The bend force calculator estimates the relationship between bend length, tensile strength, thickness, die opening, and a user-supplied bending factor. Confirm the factor with your tooling manufacturer; this model does not verify safe machine or tool capacity.

F = (k \times L \times S \times t²) / V

F = bend force
k = bending factor, unitless. Supply a value appropriate to your tooling and process; no universal default is assumed.
L = length of bend
S = tensile strength of the material
t = material thickness
V = die opening

Choose the quantity to solve for. The calculator rearranges the same formula:

k = (F \times V) / (L \times S \times t²)

L = (F \times V) / (k \times S \times t²)

S = (F \times V) / (k \times L \times t²)

t = sqrt((F \times V) / (k \times L \times S))

V = (k \times L \times S \times t²) / F

The calculator uses consistent millimeter, N/mm² and newton units for the relationship, then converts the answer to the selected result unit. lbf denotes pound-force, not mass.

Select Solve for, enter the five displayed known values and choose a result unit where applicable. Select Calculate to show the answer below the form. All quantities must be greater than zero.

Typical Inputs for Bend Force Estimates

The following are illustrative values from the original examples, not certified material properties or design inputs. Obtain tensile strength for the actual grade, temper, thickness and condition from its material certificate.

Material	Illustrative tensile strength	Equivalent psi
Mild steel	400 MPa	58,000 psi
Stainless steel	515 MPa	75,000 psi
Aluminum 5052-H32	228 MPa	33,000 psi
Aluminum 6061-T6	310 MPa	45,000 psi

Common V-Die Opening Guidelines

These broad air-bending examples are not tool-selection instructions. Follow the manufacturer’s application limits for the actual material and geometry. Bystronic’s tooling reference uses thickness-dependent opening guidance and a geometry-dependent bending factor; a fixed k is an approximation.

Material thickness	Common V-die opening	Effect on force
Thin sheet	6t to 8t	Smaller opening increases required force
General air bending	8t	Common estimating value
Thicker plate	10t to 12t	Larger opening reduces required force

Example Problems

Example 1: Calculate bend force

You have a V-die bend with these values:

k = 1.33
Length of bend = 24 in
Tensile strength = 60,000 psi
Thickness = 0.125 in
Die opening = 1 in

F = (1.33 \times 24 \times 60000 \times 0.125²) / 1

F = 29925 lbf

The required bend force is about 29,925 lbf, or about 133.1 kN.

Example 2: Calculate die opening

You know the available force and want to find the die opening:

k = 1.33
Length of bend = 36 in
Tensile strength = 58,000 psi
Thickness = 0.25 in
Bend force = 100,000 lbf

V = (1.33 \times 36 \times 58000 \times 0.25²) / 100000

V \approx 1.736 in

The calculated die opening is about 1.74 in.

FAQs

What k constant should you use for bend force?

Use a factor supported by your tooling manufacturer or validated process. The examples retain 1.33 as an assumed input, not a universal recommendation. Manufacturer models can account for thickness-to-opening ratio and other conditions. This calculator does not model bottoming or coining.

Why does thickness have such a large effect on bend force?

Thickness is squared in the formula. If the thickness doubles, the force increases by about four times when all other values stay the same. This is why small changes in sheet or plate thickness can make a large difference in required tonnage.

Does a larger die opening reduce bend force?

Yes. Die opening is in the denominator of the bend force formula, so increasing the die opening lowers the required force. A larger die opening can also increase the inside bend radius and may affect the final bend geometry, so it should be selected based on both force capacity and part requirements.