I made a fluting tool. It works very well. I found that if you bend the flange slightly as you squeeze the flutes in it forms the metal better. The tool has flat end radius on the outside rods. The inside one has a very slight taper and a radius on the end. This keeps the rod ends from putting dimples in the flange radius. To test the tool bend a flange first. It doesn't work correctly on a flat sheet.

Folded backwards to show detail.