Curved Folding

foldable=makable

Sheet metal folding

I am working on a bridge project based on a pleated and curved hypar (I attached some pictures). I was thinking to fold it using a sheet of mild steel 1.5 mm thick perforated along crease lines. The person who has to do the perforations is concerned about the design, he thinks that it is not suitable to be folded using metal. I am new to sheet metal folding and I am not sure about how metal will behave.

The model is 1200x400 mm and the distance between folds is 20 mm. Perforation is going to be made with water jet, slots are 2.5x7 mm and the distance between slots is 5 mm.

It might break or probably I will not able to fold it by hand.

 

I would be grateful if somebody could advice on it.

 

Thanks

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Permalink Reply by Gregory Epps on July 12, 2010 at 11:41
Hi Irene - this looks really nice, I hope you get to build it! For the model, at that size, 0.8mm steel or less is probably fine (1.5mm will be impossible with only 20mm of surface to hold!) and slots could be 7mm, with no width (just a cut) - but I would reduce the metal between slots to 2mm otherwise it will be hard to fold. Overall this shape will be difficult to fold in metal, as you have to slowly work up the whole model - it may be useful to tighten some string/straps around the model as you go, to avoid repeated folding and unfolding (and therefore weakening). It might be worth making some test sections, or at least have the expectation that you will make a few prototypes until you get the mix right...

Good luck - Greg
Permalink Reply by Irene Scudellari on July 12, 2010 at 16:11
Thanks Gregory,

The width of the waterjet cut is 1mm. I will make some test sections and will see how it behaves.
Do you know any company specialized in the manufacturing of sheet metal folding in London?

Irene
Permalink Reply by Gregory Epps on July 12, 2010 at 16:29
Hi Irene - I run a company called RoboFold that specialises in fabricating using curved folds. Send me an email through my profile page and we can talk. Greg
Permalink Reply by Shawn Fernandez on July 13, 2010 at 20:28
I don't know if it defeats the purpose of your project, Irene, but have you considered making each section or panel a separate piece, bending the general loft shape into each individually and then welding them together to finish the structure? If you did this you could eliminate the tabs and have a uniform and stronger seam.

Alternately you could get very accurate bend information if you treated each bent segment between the slots separately as a straight line rather than as an entire curved fold and analyze each section locally as a standard bend. Regardless, bending this by standard mechanical means (press brake) would take a very long time and many steps, but it isn't impossible out of 1.5mm thick material.

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