Originally Posted by taras0000

It has to do with the way forging aligns the grain structure of the metal. Think of a part that is made in a closedmold and is foam injected. If you were to cut it in half, you would see that the foam is densest along the outer skin with bigger bubbles in the center. Forging does something similar to the grain structure in metal. Remove some material after forging and you will remove that strong outer "skin", creating weak areas.