Now in SolidWorks 2012,  we can perform a swept flange and flatten it to capture the blank size. (Insert> sheet metal> Swept Flange) 
Just like the normal swept feature, you need to have a profile and a path. Take note that the profile should not be a close profile. It should be open sketch.
Use flat pattern to unfold your swept flange into a blank size and save directly into .DXF for manufacturing purpose. Give a try.
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