3d printers ok for protos and one off. If you are talking injection molding, you want more than one part and at a low cost per unit.
You can also machine one offs out of plastic too with a CNC mill.
Q. Is this for commercial use or just personal use? CNC mills for mold making for production are not cheep. However quality CNC mills can still make molds just slower.
My Haas TM1 can do it just fine, but it will be a slow process as I only have 6000 RPM on tap. But it would make a fine mold, however I would probably have to up the memory as a 3D mold program will be large.
Q. What are you going to do for software to program said mill? Good CAM is not cheep. Again personal or commercial makes a difference here.
Mark
2005 Haas TM-1, 4th HRT160 - OneCNC XR4 Pro w/4th - Alibre Design Expert
Metal-tech 4x4 - www.metaltech4x4.com