Hollowtech cranks

Just a slight correction: "Hollowgram" doesn't refer to Shimano at all. That's a name Cannondale uses for its own cranksets. If anything, FSA make their chainrings.

"Hollowtech II," now that's the Shimano moniker you were looking for.

@cyclesteffer

I believe you've described the process of forging. The heat works with pressure to make the metal grains line up in a single direction. The same process is used in the automotive industry for boutique wheels.

Shimanos more expensive stuff is heat treated - e.g. the metal is "cooked" in an oven, to line the grains in the metal up in the same direction. Thats also how they make thin aircraft engine blades, incredibly strong yet light, and hollow.

Any beam has to resist bending and shear forces.  Shear forces (up and down or cutting forces) are resisted by the cross section of material.  Bending is resisted by the material that is at the edge of the beam, so the material at the centre of beam does very little to resist the bending forces.  As bending forces are generally much larger than the shear forces having the material as far from the middle of the beam is the most efficient way by weight to resist the forces, that's why hollow beams are lighter and stronger.