additative manufacturing is the capable of making a gear box, but with all this type of process an amount of machining is required, and non of those systems are quick enough.
A quick CNC is an option for metal parts, but numbers is the decider and unit cost.
check this link as it can laser weld titanium to gold powder in to any shape you can design
http://www.renishaw.com/en/additive-...cturing--15239