Open die forging involves the shaping
of heated metal parts between a top die attached to a ram
and a bottom die attached to a hammer anvil or press bed.
Metal parts are worked above their recrystallization temperatures-ranging
from 1900°F to 2400°F for steel-and gradually shaped
into the desired configuration through the skillful hammering
or pressing of the work piece.
While impression or closed die forging
confines the metal in dies, open die forging is distinguished
by the fact that the metal is never completely confined
or restrained in the dies. Most open die forgings are produced
on flat dies. However, round swaging dies, V-dies, mandrels,
pins and loose tools are also used depending on the desired
part configuration and its size.
Although the open die forging process
is often associated with larger, simpler-shaped parts such
as bars, blanks, rings, hollows or spindles, in fact it
can be considered the ultimate option in "custom-designed"
metal components. High-strength, long-life parts optimized
in terms of both mechanical properties and structural integrity
are today produced in sizes that range from a few pounds
to hundreds of tons in weight. In addition, advanced forge
shops now offer shapes that were never before thought capable
of being produced by the open die forging process.
The Open Die Forging Process
Steps to produce a typical spindle-shaped part:
Rough forging a heated
billet between flat dies to the maximum diameter
tool marks the starting "step" locations
on the fully rounded workpiece.
Forging or "drawing"
down the first step to size.
The second step is drawn
down to size. Note how the part elongates with
each process step as the material is being displaced.
the rough forging for a smoother surface finish
and to keep stock allowance to a minimum.