A prototype tool can be produced in any material. The reason for this build is to prove part shape, finished dimensions, tool design, cycle time , prove a new process technique capable, and hundreds of other reasons. The biggest differances is the use of hand loaded inserts (steel, aluminum, of berrylium) versus lifters for the parts. I have seen numerous prototype tools converted to production, since they worked so well. The trick for the aluminum ones is to use ejector sleeves in the mold base for the harder ejector pins to cycle against. Rick.