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cwhetten
Posts: 1,051
Registered: ‎09-03-2008
Message 1 of 4 (516 Views)
Accepted Solution

Sheet Metal - Flat Pattern Bug

516 Views, 3 Replies
01-23-2013 02:39 PM

So here's a strange one.  This sheet metal part has two bends, and was created with a lofted flange feature on the XY plane:

 

DO Box 1.PNG

 

It was then cut by two circular profiles on the XZ plane:

 

DO Box 4.png

 

When the flat pattern is created, it seems to work just fine as long as the diameter of the circular cut is below a certain value.  Once the diameter is increased beyond this value, the flat pattern returns a cryptic error and does not compute:

 

DO Box 5.png

 

I know that the bend geometry does NOT pass through the bend axis,  so I am left guessing at what the real problem is.  I have attached the part.  The part currently has the parameter called "Tank_ID" set to 500 in.  To see the error, change the value of this parameter to 600 in.  For me, the flat pattern breaks between the values of 512 and 513 in.

 

Why does the flat pattern work at 512, but not at 513, since there is no significant difference in geometry?

Mentor
alewer
Posts: 188
Registered: ‎08-15-2006
Message 2 of 4 (502 Views)

Re: Sheet Metal - Flat Pattern Bug

01-23-2013 04:28 PM in reply to: cwhetten

Short answer: I don't know why this fails, but see the attached for a method that works.

 

It's generally bad practice to extrude or cut in this fashion: not all of your cut are perpendicular to the face. As a result, the front of your flat pattern doesn't quite match the back. Do you use flat patterns for laser or waterjet cutting? If so, this can be a big problem.

 

There are a few ways to do this. Surfaces & thicken, contour flange & cut across bend, etc. In the first attached file (2013), I've used a split + thicken to trim your contour flange. Not only does it result in square cuts (flat pattern back matches front), but it doesn't fail as your part does. I've also included a 2010 file showing this method in case you have an older version. While this method might seem sloppy (many features require), it works.

 

Give this a shot, and let me know if you have any questions or would like to see a different way to skin this cat.

Valued Mentor
BLHDrafting
Posts: 350
Registered: ‎10-12-2012
Message 3 of 4 (498 Views)

Re: Sheet Metal - Flat Pattern Bug

01-23-2013 04:32 PM in reply to: alewer

Well done alewer.

 

Those were my thoughts also. Non parallel edges and using Split/Thicken to make the cuts. Got half way through modelling it when I saw your reply. :smileyhappy:

Brendan Henderson

Web www.blh.com.au
Twitter @BLHDrafting

Windows 7 x64 -64 GB Ram, Intel Xeon E5-1620 @ 3.6 GHz
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*Expert Elite*
cwhetten
Posts: 1,051
Registered: ‎09-03-2008
Message 4 of 4 (454 Views)

Re: Sheet Metal - Flat Pattern Bug

01-24-2013 12:09 PM in reply to: alewer

Bingo, alewer!  That's exactly what we were looking for.  That is definitely the right way to do it.

 

My team wanted me to make sure to give you a big virtual high-five from all of us.  It stumped 4 of us for an entire day, so we appreciate the help!

 

And thank you, also, Brendan, for lending your vote to alewer's method.

 

Kudos for everyone!

 

-cwhetten

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