k-Factor Calculator

This calculator is based on the following concepts:

Figure 1

The blue line segment in figure 1 is where the inside bend radii

is less than a material thickness or the minimum radius as a
percentage of the material thickness, “sharp”.

The Gold line segment shows as the inside bend radius

increases the k-Factor also keeps increasing until it reaches
.5 the maximum value for “k”.

The Maroon line segment stays constant at .5 (50%) and represents a value for the Inside bend radius (Ir)

1) The physical limitations of the metal make it difficult to accomplish a bend radius less than material thickness without Coining or Bottom Bending the sheet metal.

2) When Air forming with a radius that is technically “Sharp” the bend takes on a parabolic shape as opposed to a true radius.

Making a radius measurement extremely difficult to make and by extension the value for the k-Factor hard to predict with any accuracy

3) In the bend radius, the material goes through a few changes. Those changes being that on the outside of the bend radius
longitudinal and transverse the material is being stretched or “expanding”. On the inside surface, the material is being compressed. Because compression cannot exceed expansion the maximum k-Factor cannot be greater than 50% as the compression cannot exceed the expansion.

The minimum k-Factor described by the following formula:

(4 – Pi) / Pi

Then using reverse calculations, we calculate the minimum k-Factor for an Air Bend, and that value is 0.27324

Minimum k-Factor = (4 – Pi) / Pi = 0.2723

Then taking the minimum k-Factor and subtracting that value from our maximum k-Factor we calculate a value of 0.226

0.5 – 0.27432 = 0.22568

We next take the .22568 value and divide that by 3, the number of sections represented in the gold line section.

0.22568 / 3 = 0.7558666

We then multiply the 0.07558666 by the Inside bend radius divided by the material thickness minus 1. then adding the minimum k-Factor of 0.27324 to that value.

The k-Factor then equals: .07558666 * ((Ir / Mt)-1) + 0.27324

For a Material thickness of 0.062 and an inside radius of 0.093, we would have a k-factor of .349

That is the background for the calculations. Now you can let the calculator do the work for you.

Please leave a comment on the calculator; what you thought about it, along with suggestions on how we might improve it.

Try our Springback Calculator and our Sharp Bend Indicator


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