How to unbend (flatten) a part for sheet manufacturing

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arcol
Posts: 221
Joined: Sun Nov 10, 2013 9:02 am

How to unbend (flatten) a part for sheet manufacturing

Postby arcol » Tue May 26, 2015 3:09 pm

Hi,

Here is the box I would like to get manufacture:
box_base.png
box_base.png (20.22 KiB) Viewed 1932 times
As you can see, there is basically two part going together.
The base:
box_assembly_howto.png
box_assembly_howto.png (43.54 KiB) Viewed 1932 times
And the top sheet, which is bended, but predrilled (pre lasercutted):
box_cover_drawing.png
box_cover_drawing.png (33.71 KiB) Viewed 1932 times
Here is a drawing how it is supposed to look:
box_cover.png
box_cover.png (19.3 KiB) Viewed 1932 times
The thickness is 8mm, the holes are 3mm diameter, and the bending inner radius is 8mm.

I know it is a bit heavy (8mm thickness), it is an imaginary model, the most basic example I could model.

I'll continue with more pictures and models in my next post.
arcol
Posts: 221
Joined: Sun Nov 10, 2013 9:02 am

Re: How to unbend (flatten) a part for sheet manufacturing

Postby arcol » Tue May 26, 2015 3:12 pm

Here are the dimensions of the top part:
box_cover_side.png
box_cover_side.png (27.48 KiB) Viewed 1927 times
The question is, how can I unfold this model?
What should I lasercut (which is already predrilled), so I can bend it at a different manufacturer.

Here are all the models used in the first post:
box_cover.fcstd
(71.41 KiB) Downloaded 11 times
box_base.fcstd
(43.27 KiB) Downloaded 14 times
assembly_box.fcstd
(23.77 KiB) Downloaded 11 times
Any pointers is much appreciated.
Also I read in the past about some unfolding workbench. What is the state of it?
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ektus
Posts: 141
Joined: Sat Sep 22, 2012 6:23 pm
Location: Germany

Re: How to unbend (flatten) a part for sheet manufacturing

Postby ektus » Tue May 26, 2015 4:34 pm

I would take both the drawing with dimensions and the model (exported as STEP) to the manufacturer. I'm designing bended sheet parts at work all the time (well, using CATIA V5...), and the unfolded view of the part is optional as the bending radius also depends on the bending machine available to the manufacturer. Therefore, the manufacturer inputs the STEP model into his CAM software and that one unfolds it while considering machine parameters and material properties (grade of steel, aluminium or whatever). The STEP file is used to get the overall dimensions and bore positions, the drawing confirms the dimensions and adds information as to whether the bores contain threads as well as material, tolerances and surface treatment.

For 8mm material thickness, the shortest leg should be longer than approx. 55mm, otherwise the bending machine can't handle the part.

The bent radius won't be as smooth as modelled, though, as the material will flatten somewhat, especially at the ends.


Regards
Ektus.
arcol
Posts: 221
Joined: Sun Nov 10, 2013 9:02 am

Re: How to unbend (flatten) a part for sheet manufacturing

Postby arcol » Tue May 26, 2015 5:38 pm

So I shuold not take into account compression and tencion during the blending?

Wikipedia has a nice calculation method:
http://en.wikipedia.org/wiki/Bending_%2 ... lculations

I since have found some relevant infos, like the unfolding macro:
http://www.freecadweb.org/wiki/index.ph ... alUnfolder

Add wall tool:
viewtopic.php?f=24&t=8789
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ektus
Posts: 141
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Location: Germany

Re: How to unbend (flatten) a part for sheet manufacturing

Postby ektus » Tue May 26, 2015 5:55 pm

So I shuold not take into account compression and tencion during the blending?
If you like and want, you can, but normally it's not necessary. I normally leave such to the specialists at the manufacturer. They know their machines and material and employ specialized software that performs those calculations. I do add unfolded views with dimensions, using some generic setting for compression factor and some such, but as stated earlier, mostly that's just for information.


Regards
Ektus.
duk
Posts: 55
Joined: Sun May 17, 2015 1:44 am

Re: How to unbend (flatten) a part for sheet manufacturing

Postby duk » Tue May 26, 2015 11:45 pm

the inside of the bend is under compression and the outside under tension, the neutral line is usually 1/3 of the thickness from the inside
arcol
Posts: 221
Joined: Sun Nov 10, 2013 9:02 am

Re: How to unbend (flatten) a part for sheet manufacturing

Postby arcol » Wed May 27, 2015 7:39 am

ektus wrote:
So I shuold not take into account compression and tencion during the blending?
If you like and want, you can, but normally it's not necessary. I normally leave such to the specialists at the manufacturer.
But I would like to get the sheet lasercut (at one place), THEN bend (at another place), the two manufacturing place are 80km apart from each other...
duk
Posts: 55
Joined: Sun May 17, 2015 1:44 am

Re: How to unbend (flatten) a part for sheet manufacturing

Postby duk » Thu May 28, 2015 5:23 pm

" But I would like to get the sheet lasercut (at one place), THEN bend (at another place), the two manufacturing place are 80km apart from each other...

it should work out ok if they use the same set back and bend allowance tables
duk
Posts: 55
Joined: Sun May 17, 2015 1:44 am

Re: How to unbend (flatten) a part for sheet manufacturing

Postby duk » Thu May 28, 2015 5:26 pm

the surest way is to take a sample of metal you intend to use to the bender and have them bend it to the angle you want and measure it to find the bend deduction