ENM208
Bulk deformation
Processes II
ANADOLU
UNIVERSITY
Industrial Engineering Department
– Bulk Deformation Processes in Metal Forming – II
2006
Saleh AMAITIK
Manufacturing Processes
Extrusion
Compression forming process in which the work metal is forced to
flow through a die opening to produce a desired cross-sectional
shape.
Process is similar to squeezing toothpaste out of a toothpaste tube
In general, extrusion is used to produce long parts of uniform crosssections
Spring 2005
Manufacturing Processes
Types of Extrusion
Extrusion is carried out in various ways.
Extrusion can be classified based on the following
1- Physical Configuration
• Direct extrusion.
• Indirect extrusion.
2- Working temperature
3- Process type
• Cold extrusion.
• Continuous process.
• Warm extrusion.
• Discrete Processes.
• Hot extrusion.
Spring 2005
Manufacturing Processes
Direct Extrusion
Also called Forward Extrusion is illustrated in figure below
A metal billet is loaded
into a container, and a
ram compresses the
material, forcing it to
flow through one or
more openings in a die
at the opposite end of
the container.
Starting billet cross section usually round, but final shape is
determined by die opening
Spring 2005
Manufacturing Processes
Direct Extrusion
Hollow
sections
(for
example, tubes) are possible
in direct extrusion.
The
starting
billet
is
prepared with a hole parallel
to its axis. This allows
passage of a mandrel that is
attached to the block.
As the billet is compressed,
the material is forced to flow
through
the
clearance
between the mandrel and the
die opening.
(a) Direct extrusion to produce a hollow or semi-hollow
cross-section; (b) hollow and (c) semi-hollow cross- sections
Spring 2005
Manufacturing Processes
Indirect Extrusion
Also called Backward Extrusion or Reverse Extrusion is illustrated in
figure below
Indirect extrusion to produce
(a) a solid cross-section and (b) a hollow cross-section
Spring 2005
Manufacturing Processes
Hot versus Cold Extrusion
Extrusion can be performed either hot or cold, depending on the
work metal and amount of strain to which it is subjected during
deformation.
Metal typically extruded hot include aluminum, copper, magnesium,
zinc, tin, and their alloys. These same metals are sometimes extruded
cold.
Steel alloys are usually extruded hot, although more ductile grades
are sometimes cold extruded (for example low-carbon steel).
Aluminum is the probably the most ideal metal for extrusion (hot and
cold), and many commercial products are made by this process (for
example, door and window frames).
Spring 2005
Manufacturing Processes
Continuous versus Discrete Extrusion
Some extrusion operations producing very long sections in one
cycle, but these operations are limited by the size of the billet that
can be loaded into the extrusion container.
These processes are more accurately described as semi-continuous
extrusion.
In a discrete extrusion operation, a single part is produced in each
extrusion cycle.
- Impact extrusion is an example of the discrete processing case
Spring 2005
Manufacturing Processes
Analysis of Extrusion
Extrusion Ratio
• Also called the reduction ratio, it is defined as
Ao
rx 
Af
• where rx = extrusion ratio;
Ao = cross-sectional area of the starting billet; and
Af = final cross-sectional area of the extruded section
• Applies to both direct and indirect extrusion
Spring 2005
Manufacturing Processes
Analysis of Extrusion
The True Strain in Extrusion
For ideal deformation process:
  ln rx
The actual true strain is given by the following empirical equation:
 x  a  b ln rx
Where x = extrusion strain; and a and b are empirical constants for
a given die angle. Typical values of these constants are a = 0.8 and
b = 1.2 to 1.5
Spring 2005
Manufacturing Processes
Analysis of Extrusion
Extrusion Pressure
For ideal deformation process:
p  Y f ln rx
For indirect extrusion
p  Yf  x
Where
Yf
Is the average flow stress during deformation based on
ideal strain 
Spring 2005
Manufacturing Processes
Analysis of Extrusion
Extrusion Force and Power
The ram force in direct and indirect extrusion is simply given as
F  pA0
Where F = ram force in extrusion (N), p = extrusion pressure (MPa), and A0 =
billet area (mm2)
The power required to carry out the extrusion operation is simply
P  Fv
Where P= power in (J/s); F = ram force (N), and v = ram velocity (m/s)
Spring 2005
Manufacturing Processes
Wire and Bar Drawing
Drawing is an operation in which the cross section of a bar, rod,
or wire is reduced by pulling it through a die opening.
Similar to extrusion except work is pulled through die in drawing
(it is pushed through in extrusion)
Spring 2005
Manufacturing Processes
Wire Drawing versus Bar Drawing
The basic difference between bar drawing and wire drawing is the
stock size that is processed.
Bar Drawing is the term used for large-diameter bar and rod stock.
Wire Drawing applies to small-diameter stock.
wire sizes down to 0.03 mm are possible
Although the mechanics are the same, the methods, equipment,
and even terminology are different
Spring 2005
Manufacturing Processes
Drawing Practice and Products
Drawing practice:
– Usually performed as cold working
– Most frequently used for round cross-sections
Products:
– Wire: electrical wire; wire stock for fences, coat
hangers, and shopping carts
– Rod stock for nails, screws, rivets, and springs
– Bar stock: metal bars for machining, forging, and
other processes
Spring 2005
Manufacturing Processes
Bar Drawing
• Accomplished as a single-draft operation - the
stock is pulled through one die opening
• Beginning stock has large diameter and is a
straight cylinder
Hydraulically operated draw bench for drawing metal bars
Spring 2005
Manufacturing Processes
Wire Drawing
Continuous drawing machines consisting of multiple draw dies
(typically 4 to 12) separated by accumulating drums
• Each drum provides proper force to draw wire stock through
upstream die .
• Each die provides a small reduction, so desired total reduction
is achieved by the series
Spring 2005
Manufacturing Processes
Preparation of the Work for Wire and Bar Drawing
• Annealing – to increase ductility of stock
• Cleaning - to prevent damage to work
surface and draw die
• Pointing – to reduce diameter of starting
end to allow insertion through draw die
Spring 2005
Manufacturing Processes
Analysis of Drawing
Reduction Ratio
Change in size of work is usually given by area reduction:
Ao  Af
r
Ao
where r = area reduction in drawing;
Ao = original area of work (mm2) ; and
Af = final work (mm2)
Draft
The difference between original and final stock diameters
d  Do  D f
Where d = draft (mm), Do = original diameter of work (mm), and
Df = final work diameter (mm).
Spring 2005
Manufacturing Processes
Analysis of Drawing
True Strain
If no friction occurred in drawing, true strain could be determined as follows:
Ao
1
  ln
 ln
Af
1 r
Drawing Stress
The stress that results from this ideal deformation is given by
Drawing Force
Ao
  Y f   Y f ln
Af
The draw force is then the area of the drawing cross section multiplied by
draw stress
F  Af 
Spring 2005