They also talk about forging. Forging can produce higher quality parts because metal has a grain structure. Just like wood, it's easier to break between grains than across the grain. Forging is deforming the metal without melting it. If the temperature isn't too high, it will deform the grain structure along with it. The grain can be aligned to make the metal stronger along the axis where it needs to resist the most force.

Wikipedia has a image of an connecting rod that has been etched to show the grain:

https://upload.wikimedia.org/wikipedia/commons/5/5c/ForgedCo...

You can see the grain has been stretched along the length of the narrow parts. Wrenches are another example of something that's commonly forged for this reason.