Forging is a manufacturing process in which metal is pressed,
pounded, or squeezed under great pressure into high-strength parts. This
is usually done by heating the metal, but some forgings are produced
Generally, forged components are shaped by either a hammer or a press. Forging by hammer is carried out in a succession of die impressions using repeated blows. In a press, the component is usually hit only once in each die impression.
The Forging Process
In open-die forging, the work component is not completely confined as
it is being shaped by the dies. This process is commonly associated with
large parts such as shafts, sleeves, and disks. The part’s weight
can range from 5 to 500,000 lbs.
Most open-die forgings are produced on flat sides. Round swaging dies
and V dies are also used in pairs or with a flat die.
As the forging workpiece is hammered or pressed, it is repeatedly
manipulated between the dies until it reaches final forged dimensions.
Because the process is inexact and requires a skilled forging operator,
substantial workpiece stock allowances are retained to accommodate
forging irregularities. The forged part is rough machined and then
finish machined to final dimensions.
In open-die forging, metals are worked above their recrystallization
temperatures. Since the process requires repeated changes in workpiece
positioning, the workpiece cools below its hot-working or
recrystallization temperature. It then must be reheated before forging
Impression-die forging accounts for the majority of forging
production. In impression-die forging, two dies are brought together and
the workpiece undergoes plastic deformation until its enlarged sides
touch the die side walls.
Some material flows outside the die impression, forming flash. The
flash cools rapidly and presents increased resistance to deformation,
effectively becoming part of the tool. This builds pressure inside the
bulk of the workpiece, aiding material flow into unfilled
Ring rolling has evolved from an art into a strictly controlled
engineering process. In the ring-rolling process, a preform is heated to
forging temperature and placed over the internal roll of the rolling
machine. Pressure is applied to the wall by the main roll as the ring
rotates. The cross-sectional area is reduced as the inner and outer
diameters are expanded.
Rings can be rolled into numerous sizes, ranging from roller-bearing sleeves to rings of 25 feet in diameter with face heights of more than 80 inches.
Forgings are also used in helicopters, piston-engine planes,
commercial jets, and supersonic military aircraft. Many aircraft are
"designed around" forgings and contain more than 450 structural
forgings, including hundreds of forged engine parts.
"Forged" is the mark of quality in hand tools and hardware. Pliers, hammers, sledgers, wrenches, garden implements, and surgical tools are almost always produced through forging.