AC Cobra, in the idea, this is the result I want to obtain but the piercing is distorted by unfolding. As a result, it is not a circle that is detected and the drilling cannot be done on a machine.
Tomorrow I will try the other solutions proposed by Fab camp and sbadenis.
The elliptical shape or egg which is given after unfolding is done by laser cutting or oxy-cutting to precisely achieve a result of the diameter of the hole to be able to insert a tube or a puncture that is positioned on it or in a quarter quarter...
I had started with a transition fold, as I couldn't get the center of the hole, I tried to make a square hole (starting with the idea that the point of intersection of the diagonals would be invariant), Sw didn't want to unfold anymore.
By the way, I couldn't use the unfold function with the transition fold.
For the transition folds you have to tinker! Make a small 1mm chamfer at the end of one of the edges then use it as a fixed face to unfold it and then you will have to recreate it again for the folded.
On the other hand, on a "real" transition fold, it doesn't work: impossible to select the chamfer. I tried by adding a fold on one of the edges, the same.
Funny thing, the shape of the "square" cutout
in close-up
The sketch is on a reference plane, the "normal" cut.
with this cut-out, the part does not accept either of the 2 unfolded or unfolded commands.