To unfold any non-unfoldable 3D objects to two-dimensional shapes (sheetmetal, paper, etc.) you can use approximations. E.g. unfolding of spherical surfaces (sphere, dome) can be approximated using petals, or "orange peels":
Creating of such unfolded shape for spheres of a given radius can be done in the freeware utility CADstudio SphereUnf - see www.cadstudio.cz/download
After loading, running the SphereUnf command and specifying the sphere radius you can pick the place for the unfolded shape and the number of peels for surface approximation - the minimum, 2 peels, make two circular shapes; it is recommended to use at least 8 peels.
After you cut out the peels and bond (weld) them together, you will get the approximation of the original 3D sphere.
See also a sample of such unfold - the drawing SphereUnf.dwg
The SphereUnf utility contains also the command ConeUnf for unfolding of 3D cones (incl. truncated cones).