Forging
• Oldest metal working process.
• History : Sponge iron was heated and beat
into a useful implement by hammering with a
stone.
• Now : High powered hammers and mechanical
presses have replaced the arm.
• Controlled heating and handling of the metal.
Definition
Forging is the operation where the metal is heated
and then a force is applied to manipulate the metal
in such a way that the required final shape is
obtained.
Note : Forging is generally a hot working operation
though cold forging is used sometimes.
Classification : Pressure Applied
• Forging machines mainly divided into two
categories : on the basis of pressure applied.
a) A forging machine that applies a impact load
is called a forging hammer.
b) Other that applies gradual load/pressure is
called a forging press.
Classification : Constrained Metal Flow
• Open Die Forging
• Impression Die Forging
• Flash less Forging
Contd…
• Open Die Forging : The work is compressed
between flat (or almost flat) dies, thus
allowing the metal to flow without constraint
in a lateral direction relative to the die
surfaces.
Contd…
• Impression Die Forging : The die surfaces
contains a shape or impression that is
imparted to the work during compression,
thus constraining metal flow to a significant
degree.
Note : In impression die forging the flash (extra
metal) flows beyond the die impression.
Contd…
• Flash less Forging : Work is completely
constrained within the die and no excess flash
is produced.
Open Die Forging
• Simplest case of open die forging involves
compression of cylindrical cross-section
between two flat dies.
• This forging operation is known as upsetting
or upset forging, reduces the height of the
work and increases its diameter.
Contd…
Analysis of open die forging
• Assumption/s : Forging is carried out under
ideal conditions of no friction between the
work piece and die surfaces, then
homogenous deformation occurs and radial
flow of metal is uniform throughout the
height.
Contd…
Contd…
Under ideal conditions, the true strain experienced by
the work during the process can be determined by :
where ho , hf are starting & ending compression heights
in mm.
Contd…
The force required to compress the workpart
can be given as :
F = Yf A,
where F = Force in Newton (N),
Yf = Flow stress corresponding to strain in
MPa,
A = X-sectional area of part, mm2
Contd…
• Considering the barreling effect as shown in
the figure :
Contd…
• Applying the shape factor to account for D/h
ratio and friction :
F = Kf Yf A,
Kf = Forging Shape Factor,
Problem no. 1
• A cylindrical work part is subjected to upset
forging operation. The starting piece is 75 mm
in height and 50 mm in diameter. It is reduced
to a height of 36 mm. The work material has a
flow curve defined by K = 350 MPa and n
=0.17. Assume a coefficient of friction of 0.1.
determine the force as the process begins, at
intermediate height of 62 mm, 49 mm and at
the final height of 36 mm. Also, draw the load
stoke curve.