Flat bar bender

AKA "hard way" forming, being across the width of material. Not really different than common bending or brake work (across thickness). As in the latter, material needs rigid support of the bed and clamp, such as a box & pan brake.
What is important, material runs in a very closely fit slot, to minimize buckling through the thickness, because great disparity of inner and outer radius. Lubrication helps a great deal, especially in unhardened dies. I use gear (transmission, rear axle etc) lube.
I did a post here regarding a die-set for a HF bender, danged if I can find it.

Flat bar bender - GIF