While I have been away from it since 1999,I have worked extensively with this technology.Search "Rapid Prototyping
In my time,we used 3D Systems stereolithography,which is about a liquid polymer that hardens with exposure to UV laser.It looks like plexiglas,but not strong.It would not make a working firearm.
We had a 3D Systems Actua machine,It worked like an ink jet printer,with a 90 jet print head.It shot an engineering wax.
The idea,in the 3d Solid Modeling software(I used Pro-Engineer),is sent to a processing software that slices the virtual model into 2d cross sections.Like a contour topo map slices mountains and valleys.Suppose you slice it every .003 for a contour interval.
I our Actua machine,a 2d print of one contour would be deposited.Then the workpiece platen would lower .003.A planer head would pass over and mill the deposited material to a flat,true,.003 thick layer,Then a new layer would be deposited.
The wax part has limitations.We figured out to actually print a mold pattern,so a silicone mold could be poured off the wax master.Then 2 part resins were cast in the silicone mold.We usually used urethane.
These same wax parts are usefull for lost wax castings.A ceramic shell can be formed around them,and the wax burned out.
There is a DTM process where a laser fuses a 2d layer of about anything fusable,including powdered steel.Then the platen lowers,another layer is fused.These fused powdered metal parts have little strength,but they may be filled with copper alloy,similar to molded powdered metal,sintered parts.We tried this with plastic injection mold core and cavity parts.We had problems with warp and shrink ...not real successful.
Early 90's a rapid prototype story,boyfriend shoots girfriend in face with shotgun.
Between MRI and Catscan technology,a database of her orthopaedic injury was created.So,now there is a digital model of bone frags and trauma.
3D systems stereolithography creates a 3D plastic model surgeons can look at and discuss,evaluate,and create a strategy.With Cad designer,database for a titanium armeture for the surgeons to implant and reconstruct the woman's face around is made.Using rapid prototype technology,this titanium piece was created and delivered to the surgeons.
In one surgery,they were able to open her up,debride,implant,reconstruct her face,and close.
Contrast this with initial exploratory surgeries just to see what goes on.
While rapid prototype tech has great potential,it is expensive.
A cnc machine is cheaper.You nan be just as good at making lowers with a 3 axis mill and Solid Works.Really.
You can but an AR lower for $125.A good one.