Weird unfold happenings

[gjohnston]

I have several peices of 1/8 sheet metal bent into differant shapes. I will use one for illustration.  (L) shaped. 5 1/4" on one leg and 3" on the other; (5 1/4 + 3 = 8 1/4 width). When unfolded and dimensioned it shows 5 5/32 & 2 29/32 from the bend line and 8 1/32 overall width.  The unfolded width on all (not just this one) are incorrect. Whats up? I don't think the metal stretches that much.

[JDMather]

Do you have the correct k-factor or bend table set up for the Bend Allowance?

Attach the file here.

Bend allowance is dependant on material, thickness, inside radius of bend and the total bend angle and to some extent the tooling/machine.

[blair]

From Wiki:

The neutral line (also called the neutral axis) is an imaginary line that can be drawn through the cross-section of the workpiece that represents the lack of any internal forces. Its location in the material is a function of the forces used to form the part and the material yield and tensile strengths. In the bend region, the material between the neutral line and the inside radius will be under compression during the bend. The material between the neutral line and the outside radius will be under tension during the bend.

Both bend deduction and bend allowance represent the difference between the neutral line or unbent flat pattern (the required length of the material prior to bending) and the formed bend. Subtracting them from the combined length of both flanges gives the flat pattern length

I have also inlcuded a Bend Allowance and k-factor spread sheet.