nxakt wrote:Not sure if it works with rectangles, but no reason I can see why not, impact extrusion.
I was going to say the same thing, except I think the tooling cost would kill it for low volume. 914 is right, unless you're planning to make thousands of these (or at least hundreds), hand fabrication is probably your only option if you need it in aluminum.
Investment casting would work if you can come up with a way to make the wax master without draft. It's too big to 3D print realistically, so that would require some thought.
Also, unless you're planning to contain explosions, 10mm thick aluminum looks like massive overkill. This is about 60-70 pounds of aluminum, your material cost alone could be over $250.