Hello,I have got some stl files and I need to export them to dwg or ai files. The software needs to be freeware.Thanks for your help :)

If you had access to Inventor Fusion 2013 you could import your STL files then do a "save as" to a DWG file.

What do you get in the DWG then? a polymesh or a wired surface?Would you be able to post an example?

MeshLab is free, will read STL files and export to DXF, which for all intents and purposes is almost equivalent to a DWG because it can imported into AutoCAD and saved as a DWG.Dave.
heinsite2013-08-20 10:05:34

Heinsite thans for your answer. What about the machining then?

CAD/CAM is really out of my area of expertise.  For that I'd suggest you look around for some forums to join where you can really get into the nuts and bolts of it all.  The one thing I'm fairly certain of is that the answers will be very dependent on the equipment you have or will need to work with.  Don't be too surprised however if you find severe limitations with only freeware solutions.
 
Autodesk has CAD/CAM discussions largely in the Inventor forums, but a Google search will find you many more.  Good hunting!
 
Dave.