Cold Forging at Shimano

Primo Powerbites, and now Hollowbites are advertised as being manufactured using cold forging technology. Effectively, they are smashing a blank piece of metal into the shape they want. Cold forging offers the advantage of precise control over dimensions, no need for heat treating, and aligns the grains along the surface of the part, perpendicular for forging direction. Hot forging, on the other hand, works better at aligning all of the grains of the part (up to a certain thickness, based on material characteristics), but cannot control dimensions as well.

Here is an article on Cozy Beehive about the cold forging at shimano. You'll notice the following graph, which may explain why some of the newer forged sprockets (such as Eastern's Medusa Lite, and Stolen's Mood Ring) are forged from 6061. Kudos to Primo for using a stronger, albeit tougher material to work with: