Document Sample
cold_forging Powered By Docstoc
					Brad Deeter                                ME 368                                       Exam

         Cold forging is a cold working process where the material is forced into a die and
the finished parts will assume the shape and dimensions of the die usually using a
compressive force. This process is completed at a low temperature ranging from room
temperature to a couple hundred degrees, but always below recrystalization
temperature, that is, no no microstructural changes occur. Cold forging allows the raw
material (usually a billet, wire, or bar stock) to be made into complex geometry parts.
The advantages of cold forging are high manufacturing productivity, excellent
dimensional tolerances and surface finishes, improved material properties (higher
tensile strength due to strain hardening, and strength due to grain flow produced), and
low cost. The most important considerations are die material, workpiece material, die
life, lubrication, heat treatment after forging, and hardness. The cold forging process is
most used by the automotive industry. Disadvantages include high forging pressures,
low formability, and annealing processes necessary post forging.

       Cold heading processes use a bar stock or wire stock that are fed (manually or
automatically) into a die and a punch closes the die. The punch compresses the
material and, when finished, produces a solid part of the exact size of the dies. This
process can be completed either horizontally or vertically, but is usually completed
horizontally because of the increased speed when moving from station to station.
Common parts produced are nails, bolts, and screws. This process occurs in a matter of
milliseconds, can be highly automated, and is very economical. A drawback is the size
of the press needed to provide the required force to form the part.

        Impact extrusion is a process that is used for larger parts. This process will start
with a billet (slug) instead of a bar or wire stock. Forward, backward, or side extrusion
can be used to form the part. Forward extrusion is a process where the material is
pushed through the die, and backward extrusion allows the material to be ejected in the
opposite direction of the punch. Side extrusion allows the part to exit lateral to the
direction of the punch.

       One die, two-blow is a process where an open die is used. During this process,
the rough shape is achieved in the first blow, and the completed shape occurs in the
second blow. Two die, three-blow is a similar process where, like the name states, two
dies are utilized to form a part in three blows. This process provides an increased
variety of shapes than processes that utilize just one die.

       Multiple die forming is an extension of the two die, three blow process where
multiple dies are used to produce an even higher variety of intricate, unusual shapes.
The use of more blows reduces the amount of energy needed per blow to form the final
part. Multiple-die progression uses multiple dies and allows the final shape to be
completed in less than one second.
Brad Deeter                                 ME 368                                        Exam

       Open-die forging is a process which utilizes a hammer and an anvil (die). In this
process, the material is placed on the anvil and the hammer strikes the workpiece. In
this process, the material is permitted to flow in the path of the least resistance, until
meeting the inside edge of the die. This allows for control of the grain direction, which
can increase strength. This process is used to produce parts which are round, concave,
or convex in shape. This process is ideal for art smithing and custom work.

        Ironing is a secondary process that reduces the outside diameter of a hollow part
by thinning the outside walls. This process allows the material moved to be added to the
overall length of the part. Flaring is a similar process where one end of the part is flared.
This process increases the outside and inside diameter of a hollow part. Flaring will thin
the thickness of the part, but up to two times the starting diameter can be achieved.
Differing from most cold forging processes, ironing utilizes a tensile force.

       Orbital forming is a specialty forming process that uses upper and lower dies set
at an angle. The angle, along with an orbital motion, allows the part to be formed at a
much lower force because of mechanical advantage. Orbital forming is commonly used
to produce high dimension retention with no change in the microstructure of the

        Press forging and drop-hammer forging are processes which use a press to form
the part in a die. Press forging is a slow process where the piece is put under a
continuous pressure. Drop-hammer forging happens very quickly, where the piece is
formed by a quick blow. Press forging is favorable to drop forging because press forging
allows completion of the part in one step and facilitates tighter tolerances. Drop forging
only allows for surface deformation. The disadvantages of press forging are that it is
time consuming and the part is in contact with the dies for a prolonged period of time
(reducing die life).

       Upset forging is a process where the diameter of the part is increased by
compressing its length. Upset forging is a high speed process that is usually done
horizontally to increase the speed between stations, and usually utilizes bar or wire
stock. The machines utilize split dies which contain multiple cavities. The dies open just
far enough to pass the part to the next cavity, this makes this process ideal for mass
production. Common parts that are manufactured by this process are engine valves,
couplings, bolts, screws, and other fasteners.

       Roll forging is a process where round or flat bar stock is increased in length by
decreasing the thickness to produce a symmetrical part. This process utilizes several
sets of two cylindrical or semi-cylindrical rollers, which contain multiples shapes. As the
part moves from station to station it will be formed little by little until the final shape is
Brad Deeter                             ME 368                                   Exam

formed. The advantage of this process is increased strength by favorable grain
structure. Typical products include axles, levers, and leaf springs.


Shared By: