metal or ceramic foam

That makes sense, although it seems like the energy to escape the gravity
well of the Moon might still be worthwhile when compared to the energy
required to escape the Earth's gravity well, A fact which means that when we require raw material in HEO, the moon would be a better source for it than the Earth. But this isn't the same as saying that the moon's gravity is so negligible that we might consider doing some manufacturing on the moon because we need some gravity, and the cost of going into and coming out of the moon's gravity well is inconsequential. But if you wanted to avoid gravity wells entirely, would rotational
artifical gravity suffice? Or is that just the stuff of science fiction? Not at all. There's absolutely no reason to think that centrifugal force wouldn't be useful for making materials settle or separate, and every reason to expect that it will be OK for humans (above a certain scale), and will prevent the health problems we see with prolonged exposure to 0-G. O'Neill warned us about our tendency toward planetary chauvinism. I think our tendency to feel that the moon must be better than free space for some industrial operations is yet another example.