Can someone tell me why this unbend fails?

[bhale]

If there is a sheetmetal expert out there, could you open the attached file and tell me why this sheet metal model will not unbend or flatpatteren.

Not sure what other information you might need, just let me know.

Creo 2.0 M090

Windows 7 64bit

Thanks

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[TomD.inPDX · Accepted solution]

I ran into this the other day. You have an interference in the corner of flange 1 and flange 2.

Change the miter to "-0.1" on both and it will unfold properly.

[bhale]

You really are a sheet metal expert. I have been fighting this thing half the day! Thank you very much.

[TomD.inPDX]

Happy to help, Brian

[bduncan]

Change Relative Accuracy into Absolute Accuracy.see the gif.just click it.

[bhale]

Blue Duncan

Interesting, that worked also.

Ok, now does that mean I had overlaping geometry or not? And what is the purpose of the small touching surfaces, are they supose to be there? Keeep in mind i am not a sheetmetal guy.

[TomD.inPDX]

Normally a shop would put a round punch right there to get a minimal bend relief. However, they do need some clearance because the need to overbend the part to have it relax at 90 degrees.

Blue always comes up with great solutions. Why this fails at the default accuracy settings is something I hope PTC will look at Sheetmetal still has a lot of growing up to do.

[ekoubi]

The reason the unbend fails, is because of the accuracy.

In sheet metal it is recommended to use absolute accuracy (which now is the default for sheet metal parts), and not relative.

In this part, the thickness is small compared to part size, and since the accuracy is relative, at some point the part size is big enough to make the accuracy too big to properly create the reliefs, which contain small edges which their size is proportional to the thickness.

You can see, if you make the part smaller by changing some dimensions, the unbend will work. For example if you change the height of wall BACK_WALL from 10 to 5, the unbend will work.

[bhale]

Great explanation! Thank you for sharing it.

[TomD.inPDX]

Eran, does this mean absolute accuracy is now enabled by default in Creo 3.0?

[ekoubi]

Hello Antonius,

If you create a sheet metal part, the default accuracy will be absolute. For solid parts it is relative.

If you create a solid part, and then convert it to sheet metal, you will stay with the relative accuracy. In this case it is recommended when converting to sheet metal to change the accuracy to absolute too.

[TomD.inPDX]

Interesting... you don't have to enable absolute accuracy on config.pro for a new sheetmetal part.

Even when opening an empty sheetmetal part, it has absolute .0005 accuracy.

If you then open a solid part, it is relative to .0012 and absolute is not available.

Nice tip, Eran! Nice trick, PTC