Richard Ferguson wrote:

Thanks to all for their thoughts.

A couple of comments: The material worked would be copper, aluminum,
and perhaps other metals, and is not likely to include steel.

I will think some more about the suggestion that I do not need a perfect
fit with the female die, that a slot is enough. On at least part of the
die, I need a good fit, since I am trying to form the sheet metal in two
directions, so I need to shrink/stretch the material rather than simply
form/bend it. But perhaps I don't need a good fit the whole length of
the die.

Since your targets are softer metals, you might look into using a
non-conforming die. With this approach, the female "die" is simply a
flat urethane pad (in the 80 to 90 durometer range) at least twice as
thick as the desired deformation, backed by a flat steel plate. When
pressure is applied, the urethane flows around the male die, shaping
the work material as it goes. For all its simplicity, this approach
can produce amazing results in the right application. You can get
urethane pads at MSC or McMaster-Carr; they can be reused many times.
(Other types of rubber will work but not as well.)

Bert