depending on what u got and what u want
first is the medium
what do u want to get out as the prototype?
Choices are:
woodlike
plasterlike
plastic
metal
Woodlike one operates using butcher paper (plastic lined paper)
the machine continually pulls out a sheet over the object being formed, and then uses a laser to heat the areas that are to be bonded; increase the power and it becomes a cutter for negative hole removal. Object comes out like a piece of wood, with similar machining characteristics.
#2 is plasterlike - this uses a fine dust of plaster or whatever, and a nozzle dispensing micro amounts of glue - think of it like an inkjet on steroids; there is a z axis for raising/lowering the object, and a tub for the material being bonded - the arm sweeps across and brushes the loose powder across the top of the object and then the head comes in and sprays it with the glue. then the excess (loose powder) is brushed/blown off and the object is lowered and the next clean layer of loose powder is swept on
#3 is laser based; there is a polymer that reacts to laser light (UV); the object is supported in a liquid bath of the stuff, and lowered; each layer is drawn on by the laser forcing the liquid polymer to become solid
#4 is metal sintering - same idea as #2 but you use a metal powder and a much higher power laser - gives u a metallic object which is very porous
thats the # of the systems I know about