Sheetmetal Bend

[barrykingwill]

Sheetmetal Bend

Can someone shed some light on the methodology of a bend in sheetmetal.

If one had to calculate the unbent length manually, so as to agree with Alibre's result, would you

a. Assume the plate bends with zero strain on its neutral axis, ie the outside stretches as much as the inside compresses? In which case one can use the radius of the neutral axis to calculate the unbent length.

b. The outside retains its length and the inside compresses

c. Other

Using a. I get nearly the same answer as Alibre, but it should not be a "nearly" if using the same method.

Anyone know Alibre's method?

Regards


Barry

 

[jemmej]

The actual process is simply not that precise. The type of blank/die tooling used, the ammount of pressure applied, how fast it is applied, how accurate the bend, the uniformity of the metal. Lots of variables.

In reality, most sheet metal places have their own set of tables which they use to determine the bend allowances needed in the flat piece.

That being said, I don't know what Alibre's formula is. I assume it takes into account sheet thickness and the K-factor. There are various general formulas for large material families in the Machinery's Handbook, but these just use sheet thickness and radius with a fixed factor.

Jim

 

[barrykingwill]

Can you explain the influence of the "k factor"

 

[jemmej]

My memory is hazy so If I'm in error, someone correct me

K-factor is a constant that is a ratio of material properties (modulus of elasticity being one of these). This k-factor determines how much the material will deform during the bending process (the exterior does not stretch perfectly and the interior does not compress perfectly). You do not end up with as uniformly thick a material after a bend, as you do before.

How Alibre specifically uses this number, I do not know.

Jim

 

[jwknecht]

Re:

Can you explain the influence of the "k factor"

I will put a good article on bending that I downloaded in the binaries section. It explains k-factor very well. You can reverse engineer it with your CAD program to determine it in your shop.