Stamped heat sinks are literally made from a piece of metal being stamped out in a press. A tool is made to the form of the heat sink, then, metal is moved through a stamping machine and the stamp creates the heat sinks. This too is a highly automated process and, as you might guess, once the heat sink design is complete and the prototypes OK’d, then the actual production is a relatively “simple”.  Stamped heat sinks are generally use for low power applications since they are typically low in performance. They are cheap, even less expensive than extruded heat sinks.