In fact I found, instead of doing an extrusion to have my outline, I make a leave at the 4 corners of my folded sheet metal to have my patch. The holidays must not join each other otherwise there will be an error in unfolding
Thank you for your help @gt22, I did what you told me, it works in a way, I have the flattening of my surface but I can't extract it in DXF to create my cutting program behind. I discovered the surface tab at least. Thank you.