Bending Sheetmetal in My Brake

[rgsparber]

A few years ago, I built my own brake. As I’m sure you know, building a machine does not mean you know how to operate it. It was only when I watched an excellent video on this subject did the light come on. This turned out to be the jumping-off point, and I wandered into new territory. This article presents a procedure for calibrating your brake, making bends, the theory behind these bends, which is essential for design, followed by a variational analysis that is tested on the bench. I conclude by comparing my calculated results with the video.

If you are interested, please see

https://rick.sparber.org/SheetMetalBending.pdf


Your comments are welcome. All of us are smarter than any one of us.


Thanks,

Rick

[Frank S]

Thanks for the refresher course Rick

[Carnel]

Thanx, Rick, for this excellent explanation!

[KustomsbyKent]

Nice work Rick! That was a nice write-up explaining everything.

I work for a company that bends literally tons of aluminum sheet stock every year. That k-factor is also used in 3D CAD programs, and so the manufacturing engineers work to establish and maintain that k-factor and work with the IT folks to update it in the CAD program.
Bending thousands of parts and trying to keep a tight tolerance... I think we're around 0.005 to 0.010" tolerance for bends.
For aluminum, that k-factor can vary with the grain structure as well, which runs lengthwise on the sheet.

I used to design many parts in the past when I was in a design role, now I'm more distant to it in my current role, so this was a nice refresher on this.

Folding tables are a bit more difficult to get a consistent larger radius, but a press brake can better handle the larger radius and be consistent.

Particularly for aluminum, the hardness of the material matters quite significantly. For example, we use 5052 aluminum for sheet metal....and that designation is followed by an H-number, which indicates the hardness. Higher H number means higher hardness. This matters when you are bending it, and the radius that can be bent without cracking. If your bend cracks at the edges during the bend, it will continue to crack over its lifetime and may eventually break completely.
Countermeasures would be to increase the bend radius or go to a softer grade of aluminum.
We've found a good balance using 5052-H32.

Thanks
Kent

[piloon]

From my aviation past, teh rule of thumb was 60% stretch vs 40% shrink.
One test students were made to do was fabricate a small box with a proper fitting lid.
Now that's a lot of bend calculations and precise bending.

[rgsparber]

Piloon,

Bending a box is the subject of my next article. I agree, it is challenging.

Rick