CASTING CHAMBERS
The long ten meter wide LH2 tank of an ARES ET could be used as a casting chamber.  We just have to orbit the ET instead of discard it then send it to the Moon.  More ETs will supply good high quality aluminum alloy.  It will be awhile before we can smelt aluminum on the Moon from lunar minerals.  We might also get carbon nanofiber super materials for inflatable chambers.  We need some pressure to keep castings from volatilizing as they would in the vacuum.  And some shelter for human workers.  Metals vapors might fill the air so air scrubbers would be needed and we'd only have a 3psi nitrogen atmosphere so nothing can burn since magnesium is combustible and so is aluminum to some extent.  Workers will wear spacesuits inside.  Automation will also be used.  Temperature control will be necessary.  Perhaps the nitrogen pressure in the chamber can be kept cool with a system that uses Sun shielded space radiators to get rid of excess heat.

Molds for simple casting and pressure casting will be made of plaster, alumina, silica, alumina-silica from H2SO4 leaching of anorthositic regolith and cast basalt molds might also be used for Mg.
Why not a moon bagle torus habitat and big iron plate boxes for casting chamber? See: Modular Moon Bases. Better yet, why don't we go straight for blister steel, mild about 80,000 to 100,000 psi instead of mere 20,000 to 30,000 psi pure iron, even if we have to wait months to harvest the carbon and free iron fines to make the steel with complete harvesters landed on the Moon?  Say it takes a year to get lots of blister steel, so what? We have a moon bagle to live in and lander modules also, unless we land in really cut rate Artemis Project open landers. 

By using steel, we can make a much much larger volume habitat and larger casting chambers than if we use pure iron. I am certain we will have at least twice the volume using thinner steel plates instead of pure iron. Forget using an Ares ET for casting chamber, just cut 'em all up and make stuff out of them.  Unless we can't wait to start casting. Then we might use an Ares ET, if that rocket ever gets built, of course.

With rectangular steel casting chambers the size of homes we can do a lot of work and there's no problem with accidental splashing of molten alumium or magnesium on the floor or walls.

If we land 1000 tons on the Moon could some of this be the steel rolling mill?  Or do we cast the steel rollers, shafts, frame and motor housings on the Moon for the rolling mill and import the rest like the bearings and electric motor armatures...or make even more on the Moon.  We can cast some steel out-vac. Although some will volatilize we have plenty of it. Perhaps it will form a "scab" on top as it cools and this prevents evaporation; or we could cover the iron and steel slabs with slag that floats on top of it. 

We can make steel plates for the walls of chambers and sheet steel for duct work and tubing with a cold rolling mill.  We will need tubing for cooling systems because it will get hot in casting chambers where we also do machining of metals in a temp controlled radiation shielded environment with some pressure.  We'd wear spacesuits and have air (N2) scrubbers in the 3 psi nitrogen atmosphere, so don't worry about breathing metal vapors in a closed habitation.

We will need molds for casting and plaster can't be used for steel. Same melting point. But silica, alumina or alumina-silica can be used to make molds for casting steel parts.  Plaster should work for magnesium and aluminum. We're gonna need large molds to make Mg and Al frames for vehicles and FROGs and structures. 

We can use the rolling mill to roll aluminum and magnesium to to make fuel tanks. We could boil  highland regolith in solar furnaces to get silica and alumina. The CaO or CaAl2O4 residue could be placed in H2SO4 leaching vats  made of GLAX (glass-glass composite) or iron with a sulfuric acid resistant cast basalt lining to make CaSO4 and H2O for plaster for molds.

A colleague of mine has designed a 10' x 10' x100' iron "mobile home" that would make an excellent casting chamber.  It's walls are half inch thick pure iron and can contain 3psi with a five to one safety margin.  It would make a perfect casting chamber.  Sand casting is done with wet sand. It is wetted to make it hold it's form.  Out vac the moisture would evaporate. Indoors with a 3 psi atmosphere evaporation will be much slower.  We must sieve and size the Moondust and wet it to get it just right.  This formula must be derived by experimentation. 

What do we cast in the 10x10x100 ft. iron chamber or "mobile home?"  Perhaps big steel and iron stators and rotors for generators and big electric motors?  Rollers and frames for rolling mills?  Metal ingots will be brought into chamber, melted in electric induction furnace and poured into wetted and sized sand molds for many different parts.  Evaporation will be slight.  AC units keep the "mobile home" from getting too hot to work in. 
         David A. Dietzler, 2007