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Shaping an aluminium sheet; from circle to rectangle

Shaping an aluminium sheet; from circle to rectangle

(OP)
Hi everyone,

We need to use an aluminium (1 or 2 mm thick) sheet to connect a circle (85 mm diameter) to a rectangle (80x20 mm2) which are 300 mm away.

How could we shape the sheet?

The first idea that came to my mind is to divide it in 4 to make it coincident with the rectangle faces.

The problem is what happens in the corners

Also how to force the sheet to get this form. We could make a setup in the workshop with a cylinder and the rectangle. Then we know the unfold dimensions of the sheet (because we can do it with Catia) but I'm afraid the elasticity of the aluminium won't allow this.

What do you think?

Thank you
regards,

RE: Shaping an aluminium sheet; from circle to rectangle

Google search square to round.
Your sheet will require more material in the round part than you have in the square part.
You have 2 choices ,you can add a square to round segment between the two tubes, or you can saw cut along the flat portions of your square tube ( The triangles) and weld in curved portions. You do not say what the alloy is, but if it is not a weldable alloy then you are going to have to stretch the round end of your transformer to get the diameter, if you do it in one piece.
As far as the actual shaping goes this would be standard sheet metal shop practice.
B.E.

You are judged not by what you know, but by what you can do.

RE: Shaping an aluminium sheet; from circle to rectangle

Of course the elasticity of the aluminum won't allow the bends you need.
Sheet metal forming involves plastic deformation, going way beyond the yield point/ elastic limit.

The parameter you need to look at for the sheet material is 'elongation at break'. If the calculated maximum strain in the formed part exceeds that, then the sheet will tear, crack, or otherwise fracture in forming. I'd guess Catia can report the maximum strain, or you can estimate it by mapping the formed and blank surfaces.



Mike Halloran
Pembroke Pines, FL, USA

RE: Shaping an aluminium sheet; from circle to rectangle

(OP)
Thanks for the answers; it seems this is not so easy.

I'm taking into account your opinion for the design.

The deformation is not so big so the material will stay in elasticity; I'll check with the workshop

I have upload some pictures;

http://www.subirimagenes.com/imagen-02-8604690.htm...
http://www.subirimagenes.com/imagen-03-8604691.htm...
http://www.subirimagenes.com/imagen-04-8604692.htm...
http://www.subirimagenes.com/imagen-05-8604693.htm...

RE: Shaping an aluminium sheet; from circle to rectangle

You can't get the sharp corners you've drawn on the rectangle end using any ordinary sheet metal tooling. You could weld the shape from four pieces and get close.

Find the oldest, crankiest sheet metal guy in the shop and ask what's possible.

Mike Halloran
Pembroke Pines, FL, USA

RE: Shaping an aluminium sheet; from circle to rectangle

Ok Drodrig,
You have shown in your attachments a square to round adaptor possibly welded on 4 sides. This is a no brainer for any competent sheet metal shop.
Is this what you really want? It would be easier for the shop to make this in two halves.

The most common method of fabricating this type of part is to divide the round part into short straight segments and draw lines tapering to the square corners. The part is then bent on these lines in one or two degree increments , depending on the number of lines.
If you do not want those lines, then the sheet metal shop has to use a tool called a funnel stake to bend the part around. With the thickness of metal you are calling out , this will not be an easy task, although I have done it in the past on jet engine parts. As far as the elasticity of the part, I think what you are referring to is called spring back, the fabricator will have to slightly over bend the part to get the desired form.
B.E.

You are judged not by what you know, but by what you can do.

RE: Shaping an aluminium sheet; from circle to rectangle

drodrig,
You have not told us what alloy you are using for this project, It may be that you would have to anneal the aluminum alloy to get your sharp corners, then re heat treat to get your properties back.
B.E.

You are judged not by what you know, but by what you can do.

RE: Shaping an aluminium sheet; from circle to rectangle

(OP)
Hi,

The material in principle is not important; this won't support much weight; what's important is changing the shape properly (this is to bring the light from a quartz to a phototube.

We will first try with this 0.4 mm sheet, 320 G
http://alanod.com/opencms/opencms/en/technical_dat...

Now I understand making many triangles works very well like
http://youtu.be/NnrqMkb--jU?t=1m40s

thanks

RE: Shaping an aluminium sheet; from circle to rectangle

That material is very thin for a mirror and will distort easily. However with this type of material you may be able to hand form your part, without the bend lines.
B.E.

You are judged not by what you know, but by what you can do.

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