I’m trying to model a part we currently have fabricated outside: a spiral-welded pipe made out of perforated strip. If the seam were straight I’d create the tube from a sketch with a sheet metal base flange feature, unfold it and add the perf pattern to the flat, then fold it again. This approach won’t work here because the seam is helical along the tube length.

If I thin-extrude a tube and then sweep-cut a helical groove along its length, I can’t convert it to sheet metal because there’s no linear fixed edge or face.

If I create the tube with a lofted bend between two 3D sketches based on offset helixes, it will create the sheet metal feature and I can get a flat pattern (it seems very fussy about where I trim the ends of the tube—for certain values I get “Warning: This part contains features that cannot be unbent.”) but I still can’t add an unfold feature because, again, there’s no fixed face or edge.

Has anyone solved this, or is it just not possible in SolidWorks?