Steve Graber presents great way to insert metal parts (in his case metal nut-serts) into 3d printed ABS object (it would work with PLA and other probably).
He uses hot end mounted on a drill press which heats the metal part which is then melted in the 3d printed part by pressing it downwards.
The parts looks almost like commercially produced. The fused metal inserts are probably very strongly bonded into plastic around them.
So Steve hacked and merged a hot end and a drill press to create a new tool!
Here is his explanation of the process and his contraption:
Here is the hot end mounted on the drill press: