Unbending Curve Shapes

I have made an assembly with different sheet metal parts in it. Some of the parts have curve shapes in it. Like I have a circular tube with a flange being formed on the tube end. Now I need to come up with the sheet size required to form that tube & flange.But for some reasons ProE is not allowing me to unbend these parts. I am able to unbend the simple parts like just a cylinderical tube or a conical tube. But if a part has some bend in it, it wont allow me to unbend it.Can anybody help me in this.


Thanks


Raza


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