DXF Flat Pattern > Curved Sheet Metal Part: Basic issue seems complicated?

[carl_maltbyKXZSU]

I work in sheet metal fabrication and often take in part-baked designs of complex constructions from clients. I hit a strange "simple" issue that I can't see an easy way of resolving without rebuilding hundreds of parts from scratch. Essentially, the solutions should be simple but doesn't appear obvious.

So I have a STEP file of a large assembly with several parts having an single radius rolled over the entire length. Inventor refuses to Flat Pattern from STEP due to discrepancies in the SW > STEP > Inventor transfer, but that's maybe fine. I also have DXFs of the Flat Patterns from SW.

Now this is where it becomes less clear on how best to proceed. The DXF Flat Pattern outlines have no guaranteed edges that are parallel to the centreline of the bend over the entire part. This one part has a flat top edge which is an outlier, most are a gentle "U" shape of some description. In principle it should be simple; this is a flat pattern with a red bend centreline of a known radius. I just don't seem to find a way to make it happen.

[kacper.suchomski]

Hi

Inventor has no problem with flat pattern for step files.

Inventor also has no problem with importing SW models (apart from the latest version, which always requires reaction time).

However, you cannot create flat patterns in the case of:

1. Multi-body models and assembly files - you need to create/open single part files.
2. Damaged geometries - thickness changes, overlapping geometries, etc.
3. Non-linear bending - embossing, stamping, damage, rib.

The problem is probably in the workflow or in a mismatched dxf export template.

[carl_maltbyKXZSU]

Thanks for the swift response. These are single Parts brought out of composite STEP assemblies. Unfortunately it seems that either the original SW files (which I do not have access to) were degenerate in some manner going to STEP, or they ended up so after coming via Inventor's STEP import filter, causing Inventor to error out of producing Flat Patterns. I can validate/edit the STEP parts in say, Rhino, but this is suboptimal for several hundred unique parts. Some are fixable by directly Deleting faces and rethicknessing the geometry, however some are damaged on both faces either side of the bent part Thickness. There are no fundamental features to complicate what should be a simple cylindrical unwrap.

Sidestepping the STEP (no joke intended) route, there should be a way to reconstruct the part from 2D/DXF, however this appears unclear also.

[kacper.suchomski]

It's impossible to evaluate anything without real files. 

[carl_maltbyKXZSU]

As requested.

The STEP part does not seem to resolve the internal 9561mm internal radius which I presume is why a 2mm flat pattern cannot be derived from it. Equally I cannot see a simple method to take the DXF flat pattern and apply that radius around the centreline.

[kacper.suchomski · Accepted solution]

The geometry is faulty. This is clearly visible in the video.

But above all, it doesn't seem like it can be done without stretching/straining.
The geometry suggests that this part cannot be obtained by "linear" machining.

In this case, offset the inner surface by a factor of K to obtain a neutral geometry, then use the Unwrap tool.

[carl_maltbyKXZSU]

Thank you for your dedicated attention Kacper. In your opinion, is there a good way second method to re-develop the geometry using the DXF to apply an overall curve to a flat sheet part?

[kacper.suchomski]

If the element is not linearly bent, automatic flat bending will not be supported.