I don't think you manage to create a weld bead with the function: "Weld bead" or "Fillet weld bead", in my opinion you should make this bead with an extrusion, or even a sweep depending on the shape of your part.
Don't fuse the volume or you won't be able to unfold.
This is indeed a solution for Arno, but since it is a sheet metal part, he will not be able to unfold it in one go, but your answer could be useful for people who would like to do this on a "non-sheet metal" part
The improvement of being able to put a cord on a piece composed of a single body could be quite good.