Forging presses are widely used to
form car wheels, bushings, gears,forged fittings - Tee , Elbow , unions
and other parts. These presses utilize hydraulic pressure to exert
enough force for pressing the steel or other metal into the desired
shape.
Some of the common forging methods and their applications include the
following :
Hammer Forging : Preferred method for individual forging. The
shaping of a metal, or other material, by an instantaneous application
of pressure to a relatively small area. A hammer or ram, delivering
intermittent blows to the section to be forged, applies this pressure.
The hammer is dropped from its maximum height, usually raised by steam
or air pressure. Hammer forging can produce a wide variety of shapes and
sizes and, if sufficiently reduced, can create a high degree of grain
refinement at the same time. The disadvantage to this process is that
finish machining is often required, as close dimensional tolerances
cannot be obtained.
Press Forging : This process is similar to kneading, where a
slow continuous pressure is applied to the area to be forged. The
pressure will extend deep into the material and can be completed either
cold or hot. A cold press forging is used on a thin, annealed material,
and a hot press forging is done on large work such as armor plating,
locomotives and heavy machinery. Press Forging is more economical than
hammer forging (except when dealing with low production numbers), and
closer tolerances can be obtained. A greater proportion of the work done
is transmitted to the workpiece, differing from that of the hammer
forging operation, where much of the work is absorbed by the machine and
foundation. This method can also be used to produce larger forgings, as
there is no limitation in the size of the machine.
Die Forging : Open and closed die operations can be used in
forging. In open-die forging the dies are either flat or rounded. Large
forgings can be formed by successive applications of force on different
parts of the material. Hydraulic presses and forging machines are both
employed in closed die forging. In closed-die forging the metal is
trapped in recessed impressions, which are machined into the top and
bottom dies. As the dies press together, the material is forced to fill
the impressions. Flash, or excess metal, is squeezed out between the
dies. Closed-die forging can produce parts with more complex shapes than
open-die forging.
Die forging is the best method, as far as tolerances that can be met,
and also results in a finished part that is completely filled out and is
produced with the least amount of flashing. The final shape and the
improvement in metallurgical properties are dependent on the skill of
the operator. Closer dimensional tolerances can be held with closed die
forgings than with open die forgings and the operator requires less
skill.
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