How does Forging Strengthen Metal?

When it comes to manufacturing a metal component, the 3 most common manufacturing processes are: 

Casting: The metal is molten and poured into a 'cast' which takes the rough form of the item to be produced, cooled then usually put onto a cnc machine to be finished e.g Camshafts. No grain flow is present nor does the item have an increased directional strength. This is the most cost efficient method of steel-product manufacturing, but the end-product is not so strong/durable.

Machining: This is what companies are referring to when they say 'Billet'. The plate or billet is simply placed directly onto the cnc machine and is cut until finished. Most companies will preach 'Billet' as being the strongest as it retains the original grain flow, however, this grain flow is uni-directional, therefore on items which are not symmetrical (i.e Gears), the machining exposes the grain ends which makes the item more susceptible to fatigue and stress. This is a very cost-inefficient method of steel-product manufacturing (due to waste material), but is the most versatile of all methods when it comes to custom one-off items and, where a 'cast' item is not strong enough, this method is used for small-quantity production. The end-product is only as strong as the 'cut' it was made from (heat treatment etc aside), which is why the choice of steel is important. 

Forging: With the most commonly used method, the billet is heated and placed into a special kind of tooling called a 'die'. The heated metal is put under extreme pressure and forced into the shape of the 'die'. Unlike the 'cut' that it once came from, the grain flow is directional and has been orientated in a way to increase strength/toughness (i.e increases steel ductility and impact resistance). Also, as no grain ends are exposed, a forged item is less susceptible to fatigue and stress. 

Forging Strengthens Metal

• Forging produces predictable and uniform grain structure and flow characteristics which Increase Directional Strength

• Forging eliminates internal voids/gas pockets that weaken metal parts, providing superior chemical uniformity and Increased Structural Strength

• Forging ensures proper orientation of grain flow, thus maximizing fatigue resistance and Increasing Impact Strength

In short, the forging process adds an approx. 30% increase in strength/toughness over original billet it was made from. Compared to casting (forging vs casting), the initial tooling costs of forging are much more expensive, thus it is required to manufacture in high quantities to 'break-even' on the initial expense. But due to the advantages of forging, this is a very cost-efficient method for large volume production.