2. INTRODUCTION
WHAT IS FORGING?
Forging is a manufacturing
process involving the shaping of
a metal through hammering,
pressing, or rolling.
These compressive forces are
delivered with a hammer or die.
Forging is often categorized
according to the temperature at
which it is performed—cold, warm,
or hot forging.
HISTORY OF FORGING
The art of forging dates to at
least 4000 BC and probably earlier.
Metals such as bronze and iron were
forged by early man to produce hand
tools and weapons of war.
The earliest recorded metal
employed by humans appears to be
gold. Small amounts of natural gold
have been found in Spanish caves
used during the late Paleolithic
period which was around 40,000 BC.
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3. CLASSIFICATION OF FORGING
Forging is done by hand
or with the help of power
hammers. Sometimes
hydraulic presses are
also used for forging.
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5. Under the action of the compressive forces due to hammer blows, the
material spreads laterally in a direction at right angles to the direction
of hammer blows. Obviously, brittle material like cast iron cannot be forged
as it will develop cracks from the blows of a hammer. An ordinary blacksmith
uses an open-hearth using coke as fuel for heating the metal and when it has
become red-hot, blacksmith’s assistant uses a hand held hammer to deliver
blows on the metal piece while the blacksmith holds it on an anvil and
manipulates the metal piece with a pair of tongs. This type of forging is
called “HAND FORGING” and is suitable only for small forgings and small
quantity production.
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7. FORGING OPERATIONS
Basic forging operations employed in giving required shape to the work piece
are described in the next following slides.
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8. UPSETTING
It is the process of
increasing the cross-
section at expense of the
length of the work piece.
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DRAWING DOWN
It is the reverse of
upsetting process. In this
process, length is
increased and the cross-
sectional area is reduced
10. BENDING
Bending of bars, flats,
and other such materials
is often done by a
blacksmith. For making a
bend, first the portion at
the bend location is
heated and jumped (upset)
on the outward surface.
This provides extra
material so that after
bending, the cross-section
at the bend does not
reduce due to elongation.
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11. Punching is usually followed
by drifting, forcing a drift
in the punched hole through
and through. This produces at
better hole as regards its
size and finish.
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PUNCHING AND DRIFTING
Punching means an
operation in which a punch
is forced through the work
piece to produce a rough
hole. The job is heated,
kept on the anvil and a
punch of suitable size is
forced to about half the
depth of the job by
hammering. The job is then
turned upside down and
punch is forced in from
the other side, this time
through and through.
12. SETTING DOWN AND FINISHING
Setting down is the
operation by which the
rounding of a corner is
removed to make it a square.
It is done with the help of
a set hammer. Finishing is
the operation where the
uneven surface of the
forging is smoothened out
with the use of a flatter or
set hammer and round stems
are finished to size with
the use of swages after the
jib has been roughly brought
to desired shape and size.
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13. FORGE WELDING
Forge welding is a solid
state-welding that joins
two pieces of metal by
heating them to a high
temperature and then
hammering them together.
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15. When a large forging is required, comparatively light blows
form a hand hammer or a sledge hammer wielded by the striker will not
be sufficient to cause significant plastic flow of the material. It
is therefore necessary to use more powerful hammers.
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16. KINDS OF POWER HAMMERS
Various kinds of pwer hammers powered by electricity, steam, and
compressed air have been used in forging.
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17. 17
A SPRING HAMMER
It is a light hammer
powered by an electric
motor and gives repeated
blows when it is operated
by a foot operated
treadle. This type of
hammer is now obsolete and
was best suited for small
forgings.
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PNEUMATIC POWER HAMMERS
It works by two cylinders, one at
the back and another one at the
front which is the one that
impulses the stem for the stroke.
The motor for the power hammer
moves the rod of the back cylinder
or compressor and the compressed
air goes to the front cylinder
through the valves that control
the stroke displacement. They are
used in many blacksmith workshops
to make all kinds of forging
ornamental pieces which eases the
job of molding hot steel.
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STEAM HAMMERS
A steam hammer, also called a
drop hammer, is an industrial
power hammer driven by steam
that is used for tasks such as
shaping forgings and driving
piles. Typically the hammer is
attached to a piston that
slides within a fixed cylinder,
but in some designs the hammer
is attached to a cylinder that
slides along a fixed piston.
21. Usually, the bottom surface of the tup and the top of the
anvil is flat as in the case of hand forging, but to increase
production and cutdown cost, dies are often used.
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22. TYPES OF DIE FORGING METHODDS
Three types of die forging methods are prevalent.
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23. 23
OPEN-DIE FORGING
In this type of forging, the metal is never completely
enclosed or confined on all sides. Most open dies forging are
produced on flat, V or swaging dies. Swaging dies are usually
round but may also be of other shapes.
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IMPRESSION-DIE FORGING
In impression die forging, the work piece is pressed between
the dies. As the metal spreads to fill up the cavities sunk
in the dies. The requisite shape is formed between the
closing dies. Some material which is forced out of the dies,
are called “flash”. The flash provides cushioning for the
dies, as the tup strikes the anvil.
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CLOSED-DIE FORGING
Closed-die forging is very similar to impression-die forging,
but in true closed-die forging, the amount of material
initially taken is very carefully controlled, so that no
flash is formed. Otherwise, the process is similar to
impression die forging. It is a technique which is suitable
for mass production.
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DROP STAMPING OR DROP FORGING HAMMERS
A machine consisting of an anvil or base aligned with a
hammer that is raised and then dropped on molten metal, used
to forge or stamp the metal resting on the anvil. With a
gravity drop hammer, the upper die is attached to a ram and
is raised by either a board, belt, or air (Figure 11.8). It
is then allowed to fall freely to strike the workpiece. In
power-assisted drop hammers, air or steam is used against a
piston to supplement the force of gravity during the downward
stroke.
28. Hot forging calls for work pieces to be heated to the
correct forging temperature as mentioned before. In case the cross-
section of the material to be forged is thick, we should allow enough
“soaking” time for the heat to travel from the surface to the core of
the material.
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29. What to remember:
Allow a soaking time of 30 mins. for every 12-15 mm of
cross-sectional thickness.
It is important that the cross-section should get heated
to uniform temperature.
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30. Good Forging Practices:
Good forging practice calls for a reduction of cross-
section by roughly 40%.
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One should remember that forging is not only a process
of altering the shape of raw material to that required
but this process can result in improved mechanical
strength of the forged component as well.
To use as few “heats” for completion of forging as
possible.
It is important to finish forging/hammering operations
when the jobs has acquired a sufficient low temperature.
32. Occasionally, high capacity hydraulic presses are used
for forging and the metal is shaped by squeezing action of
the press rather than hammering action of hammer. Close dies
are used with impressions sunk in both dies, the upper die is
fixed on the ram and the lower die is platen of the press.
Presses are usually of a vertical configuration. Presses
produce forgings of a superior structural quality.
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34. For specific jobs like mass manufacture of bolts and
nuts form bar stock, special forging machines have been
developed. These machines work alongside a furnace in which
one end of bar is heated for some length. The heated end of
bar is then fed into the machine. With the help of dies and a
heading tool, the hexagonal head of the bolt is forged by
“upsetting”. These machines are in reality horizontally
mechanical presses which can be operated by a foot pedal. The
die consists of two halves and a heading tool
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35. The sequence of operation:
After the bolt head is
forged, the bolt of
required length can be
had by shearing the bar
at an appropriate place.
The bar is then again
inserted into the
furnace for heating and
the whole process is
repeated.
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37. The common forging defects can be traced to defects in
raw material, improper heating of material, faulty design of
dies and improper forging practice.
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38. Most common defects present in forgings are:
Laps and Cracks
Laps and Cracks at corners
or surfaces lap is caused
due to following over a
layer of material over
another surface. These
defects are caused by
improper forging and
faulty die design.
Incomplete forging
Either due to less
material or inadequate
or improper flow of
material.
Mismatched forging
Is due to improperly
aligned die halves
Scale pits
Due to squeezing of scales
into the metal surface
during hammering action
Burnt/overheated
metal
Due to improper heating.
Internal cracks
Internal cracks in the
forging which are caused
by use of heavy hammer
blows and improperly
heated and soaked
material.
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Fiber flow lines
disruption
Due to very rapid plastic
flow of metal.
40. The forged components may be subjected to severe
stresses in service. To improve service of life, to improve
properties, to remove internal stresses and sometimes to
improve the machinability, forgings may be given a suitable
heat treatment after completing forging operations. Most
common heat treatment given is normalizing.
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42. Limited formability at room temperature restricts the
use of cold forging to low and medium carbon steels and for
products where not much deformations is required to obtain
final form. Usually the stock is in the form of wire or thin
rods at one end of which a head is formed in cold upsetting
operation. Usually a mechanical press is used. Some typical
products include nails, small diameter rivets pins, brass
bolts etc.
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