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

Bend Force Calculator

Enter any 5 values to calculate the missing variable










Bend Force Formula

The bend force calculator uses the standard air bending force relationship between bend length, material tensile strength, sheet thickness, die opening, and a tooling constant.

F = (k*L*S*t²) / V
  • F = bend force
  • k = bending constant, unitless. A common value for V-die bending is 1.33.
  • L = length of bend
  • S = tensile strength of the material
  • t = material thickness
  • V = die opening

If one input is missing, the calculator rearranges the same formula to solve for that value:

k = (F*V) / (L*S*t²)
L = (F*V) / (k*S*t²)
S = (F*V) / (k*L*t²)
t = sqrt((F*V) / (k*L*S))
V = (k*L*S*t²) / F

The calculator converts your selected units to a consistent base system before calculating. Length, thickness, and die opening are handled as inch-based dimensions internally. Tensile strength is handled in psi internally. Bend force is handled in pounds internally, then converted back to your selected output unit if needed.

The calculator functions as a missing-variable solver. Enter exactly 5 of the 6 values, leave the unknown value blank, and the calculator solves the blank field using the appropriate rearranged formula.

Typical Inputs for Bend Force Estimates

These values are common starting points for estimating press brake tonnage. Actual values can vary by material grade, tooling, bend method, grain direction, and bend radius.

Material Typical 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

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*24*60000*0.125²) / 1
F = 29925 lb

The required bend force is about 29,925 lb, 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 lb
V = (1.33*36*58000*0.25²) / 100000
V = 1.735 in

The calculated die opening is about 1.74 in.

FAQs

What k constant should you use for bend force?

For a common V-die air bending estimate, use 1.33. The exact constant can change with the tooling style, bend method, friction, and setup. If you are matching a known press brake chart or a shop standard, use the k value from that source.

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.