# Modeling Bent Sheetmetal

Need help with modeling bent/folded sheet metal (manually).

I have been extruding an irregular shape and then wireCutting to section into a bunch of parts that I’m then rotating. However, its not an accurate modeling of the fabricated parts.
Most helpful if someone can provide a verbal description of the process needed to get a “rolled fold” as show in image.

3dm. file is posted here:
[https://www.dropbox.com/sh/8xz8j0thywvzdok/AABVPCW5a_j3SJha8RHvc0SLa?dl=0]

Up front, firstly, if you could draw your object, with the proper radii, and then use a simple extrusion, it would be good to do so.

Without special plugins, I have modeled bends by using a transform/flow along curve.

Generally, I create my shape, create a source and destination bend curve (selected), and have Rhino wrap the part around the bend. The bend radius must be appropriate. The lengths must be the same, but for no plug-in, it works. I usually color these curves magenta so they stand out against my blue curves.

Though, you have some pretty tight box-style bends. From the centers of the petal-like objects, I might radially split the object ( to the center of the triangles and pentagons), make the bends, and then union the result.

The odd thing about doing it this way, to some degreee, where you have distortions, you likely will in real life, though not that it was done with Finite-Element.

Because there are often more than one solution, you could also clip the inner petals, and then create curves which could be extruded to create only the the raidius area, and then join them. The curves would have to be rotated in three dimensions, to do an extrusion. The edge of the clipped edge could be selected for an extrusion Direction (option) to make sure that it is true to the edge, and not Euclidian (xyz) space.

Thanks! Brenda
Regarding initial drawings, gives me a couple ideas to pursue.

Brenda, looking at your two centered yellow lines (one vertical and one bent)… You are flowing the punched plate form along the bent line? If so, was the un-bent plate extruded from a line drawing?

Yes, you can see the unbent lightweight extrusion, which upon bending becomes a polysurface behind the scenes. The blue outlines are what it was extruded from, as well as a few others.

One curve line is the reference/source curve, and the other is the desired shape/destination.

The desired shape curve is really 2 lines and a radius curve made by a fillet curve operation.

I suspect that somewhere I changed this part and didn’t update the source/destination splines. Generally, I like to keep them as long as the part. These splines are yellow because they are selected, but I usually make them magenta, so that they are distinguishable from the others lines/curves.

This technique can be used with successive bends, but in order to do your box-brake overlapping self-shadowing style bends, you likely will need to section a copy of your part, do the bends, and union the pieces.