Create sheet metal flat patterns

gvisca44

Hoping I can engage assistance ...

My company designs & manufactures a small amount of stuff in sheet metal. In the past, we have engaged designers who generally do the CAD work in Solidworks - which when complete is then shipped off to the metal fabricators for laser cutting and folding - and returned to us for assembly and integration. Each product we produce consists of between 50 to 100 metal parts.

I would prefer to be in a position to perform the CAD work myself (I have been using SU for many years). Designing each product, along with each part is a simple thing in SU.

Where I am struggling is producing the flattened components for metal fab. Doing this manually is easy enough ... just too labourious and consequently error prone!

So I need to take each 3D modelled part and:

Create a flattened "blank" for laser cutting.
Represent that "blank" with fold lines/angles/direction (labelled dimensions) for the press brake operators to program.

The most important point to consider here is that my parts have a thickness, and a fold is a radius, not a perfect intersection of two faces. I have looked at:

Jim Foltz's "unfold" tool - and by my understanding it assumes the face has no thickness - and a fold is an intersection of two faces.
alexschreyer's "unwrap and flatten" faces - and again - I dont think it takes into consideration that a fold is a radiused bend in the metal. Equally, if I was to use this to unwrap each face of an SU surface to a single plane, the resulting blank would be the wrong size (each face is flattened "as is"). The magnitude of the error would also depend on whether I unfolded the inside faces or the outside faces of each bend (whereas the industry sheet metal calculation methods use a nominal neutral line part way through the thickness of the material (the K-factor).

So - I am looking to write an extension that accomplishes this.

It will take an SU component as the part to be unfolded (we create an individual .SKP file for each part, and then we combine them into sub-assemblies - which are further combined into the overall final assembly).
The first face would be selected by the user, and the extension will unfold the selected face and all adjacent faces. It would essentially be creating a 2d drawing of the sheet metal blank, so would only work on a single side of the 3D component.
As a bend radius is encountered, it will undertake the calculations for each fold to apply the necessary bend deduction/allowance onto the 2D drawing (maths is easy based on bend radius, material thickness and K-factor).
It must take into consideration that faces may have holes / slots / and other cuts through them (for rivets, bolts, cable connectors etc. etc.).
It must also take into consideration that surfaces (the fold) may also have holes / slots / cuts that pass across them or along them.
As a surface is encountered, the extension must determine whether the fold is UP or DOWN (for representation on the 2D drawing for the press brake operator).

I have started an extension simply to work out methods to solve problems at the moment).

Takes the selected faces from the user.
Looks at adjacent faces. If perpendicular - ignore as these are assumed to be cuts.
If not perpendicular - assumed is a fold. Look at all faces that make up the surface & ascertain radius (thanks to a code snippet by thom thom).

... but I am currently struggling to determine the fold (surface) direction relative to the selected face.

If surface is concave - fold direction is up.
If surface is convex - fold direction is down.
if vector normal converges with selected face normal - fold is up (I think ... 3d vectors are new to me).
If vector normal diverges with selected face - fold is down.

Attached are a series of test components, each with their flat pattern represented. Note that I have left some internal lines and faces in-situ to represent fold radius boundaries. In reality, these are not required.

Any assistance is appreciated.

Unfold Test Shapes.skp