Can anybody inform me about a prototyping machine that can build a model using metal (I don't know if this technology exists)???? Or could you recommend me a particular forum for this kind of question?
Do a Google search with selective laser sintering metal and find dozens of documents and service suppliers that protoytype metal parts by sintering it layer by layer with a laser out of metal powder. Don't rely on those parts as it were castings or milled parts, but they come pretty close!
Here is a process where parts are cast in a plaster mold made on a z-corp 3D printer. For those not familiar, the Z-corp machine, it is one the fastest and cheapest rapid prototype machines out there. I think you might be able to get better and cheaper metal parts than with SLS.
This is the company who makes the Z-corp machine. Contact them to find a foundary using the zcast process: