To fill a mold? yep all the time. Aluminum doped epoxy is used ALLLL the time for making vacuum formed plastic parts. Basically a CNC machine creates a mold from a CAD file, then the epoxy is poured. Also, a blank can be poured and then milled from there. Vacuum formable sheets of ABS, polyurethane, polypropelene, TPO, PVC and other plastics are heated to a specific temperature then placed over the aluminum doped epoxy tool and vacuum is applied to suck the soft plastic down onto the tool. It is then released and a part is made
3d printers don't really work that way. 3d printers bond powdered polymer layer by layer to form a solid 3d object. Epoxies can't be used that way. Unless you had a 3d printer that mixed the epoxy right before "drawing" a layer then instantly curing it with a UV laser or something, but the end product would look very rough due to how liquid most epoxies are when they are first mixed. There are giant prototype 3d printers that use concrete... which is a similar process to epoxy, it's a chemical reaction to create a rigid structure... from the tests that I've seen the end result merely looks okay.
Old rapid prototypers (3d printers) used a bath of liquid polymer and a laser would draw each layer on the surface of the bath, as the level incrementally increased, but intense external heat from the laser was required to harden the polymer. Epoxies use a chemical reaction cure the mix.