Hello everyone, I would like to unfold a sheet metal cylinder with an outer radius of 3000 ep 2
using the K factor for unfolding, the problem is that having fixed the K factor at the minimum, (0.01) I am always too long, (test done on a rolling machine) whatever, does anyone have an idea. Thank you for your answers, I'll put a screenshot
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Marco.
Hello,
I would say better to have to cross-check!
The rolling operations are not as precise in theoretical calculation as for bending ops. Especially when it comes to a developed length of more than 18m.
If you subcontract this achievement, the S/T will apply an overlength to you before welding ends
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Hello, calculating with the neutral fiber we find 18843.3mm, for a thickness of 2mm we find upper surface: 18,849.6 mm and lower surface: 18,837.0 mm
In SOLIDWORKS, the K-factor and bend loss functions are intended for localized bends (press brake bending), not for continuous cylindrical rolling.
To get the value in solidworks:
If your outside radius is to be 3000 mm:
- Inner Radius to Enter: 2998 mm
- Thickness: 2 mm
- K factor: 0.5
Then the neutral radius becomes: 2998+0.5x2=2999
and the theoretical development:
18843.29 mm
Boilermakers will generally work with neutral fiber.
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18836 was already too long 
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At the same time, 3-4 mm more on such a press, it doesn't change much on the final diameter!
And quite few dealers of 18m long sheet metal!
The clearance will likely be filled or deformed by the weld.
For me, what I was taught in boilermaking for neutral fiber, K=0.5mm for sheet metal less than 3mm and K=0.33 for thickness greater than 4mm.
For big Ø the dev doesn't change that much, the difference once ridden is very minor. On a small Ø it remains more pronounced
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If the guy doesn't cut straight, 3mm with an angle of 3° on 1m is a lot 
Hello @marc_malavieille ,
" The sheet metal is too long ", an interesting question.
A little question about the techniques used for these long sheets...
First thought: winding a 2 mm thick sheet metal, initially flat, over a radius of 3000 mm keeps the material in the elastic range, which means that the neutral fiber is in the middle of its thickness.
The advantage of the rolling operation is to force the sheet metal, by plastic deformation, to approach the final cylindrical shape (radius 3000 mm).
With a huge radius-to-thickness ratio.
So, if we refer to the uses of sheet metal: K = 0.5.
And the theoretical length indicated by @Scofield1 would be the correct one: 18843.3 mm.
Second thought: the measure.
How is the length of the sheet measured, probably unwound from a coil? Between the theoretical length and the " suitable " length of 18833.7 mm, there is only about 10 mm difference, or 0.05% of the total length, half a millimeter per meter...
Are we in the precision zone of the measuring equipment?
Still at the level of measurement: how is the " suitable " length of 18833.7 mm validated. I assume that after driving, the diameter of the cylinder obtained was measured.
Here again, with what means, what precision?
Thank you for enlightening me...
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