The photos show the two die halves -- the cover half and the ejector half. 

Note how each die insert is contained in the larger, heavier die frame.  With the proprietary steel alloy, the diecasting tool has a demonstrated life of over 150,000 "shots" before tool refurbishment is necessary. 

This is a 4X improvement in tool life compared to standard tool steels and is a major cost savings over the production life of the heat sink blocks. 

The molten aluminum enters the die cavity at  over 850C/1200F.  During the die casting operation, the temperature of the tool is controlled with active water cooling through channels in the die frame.  This prevents excessive heat-build up and thermal damage to the tool. (The cooling line connections are seen on both sides of the die frames.)