You left out a really important bit of information........which way it "curves". There are four simple possibilities, of which two are just "handed", and the extreme difference between bending "in" or "out".
I added a layer of > marks. (You should make your newsreader indicate quotes by adding > markers at left of quoted lines.)
Your answer isn't perfectly clear to me, but I'm assuming the axis of the bend is perpendicular to the long axis of the channel and that the channel has a flat bottom 75mm wide which will bend "the easy way", while the 15mm sides are bending "the hard way" and in compression.
How much crumpling of the sides can you tolerate? Crumpling will be hard to avoid unless you have a tight-fitting steel die outside the channel, and a tight-fitting 100mm-radius steel former inside the channel, to form the bend on your press. If you make the die and former with thick MDF, some crumpling probably would occur but might be tolerable.
If you will be welding along the flanges anyway, you could cross cut them half a dozen times in the bend region and then hand bend the base of the channel to the right radius.
On Fri, 30 Jul 2010 05:29:12 +1000, "Why is everyone so cruel" wrote the following:
So, endwise, the channel is ___ ___ , not a plain U or J channel? |__|
I was going to suggest a metal stretcher, but it would only stretch the flanges and your radius might be too tight for that. I wonder if you could rig a ring/band roller to do those. You'd probably need something fit inside the U to keep it from collapsing, and to hold up the flanges.
-- It is pretty hard to tell what does bring happiness; poverty and wealth have both failed. -- Kin Hubbard