They are called dies ( or molds when you shoot plastic in them)

I repair these bad boys !

Basically you melt down aluminum to a liquid form and shoot it in between the 2 halves - when they are closed up in a hydraulic press.

And it forms a part

Robot grabs the part and cools in a quench tank …

In this case we are making parts for Mercedes Benz and BMW

But Ive also worked on molds that make plastic parts for STIHL and Husqyvarna