enm208 bulk deformation processes ii anadolu u n i v e r s i t y industrial engineering department...
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ENM208
Bulk deformation Processes II
ANADOLU U N I V E R S I T YIndustrial Engineering Department
– Bulk Deformation Processes in Metal Forming – II
2006
Saleh AMAITIK
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Manufacturing Processes
Spring 2005
ExtrusionCompression 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 cross-sections
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Manufacturing Processes
Spring 2005
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
• Cold extrusion.
• Warm extrusion.
• Hot extrusion.
3- Process type
• Continuous process.
• Discrete Processes.
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Manufacturing Processes
Spring 2005
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
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Manufacturing Processes
Spring 2005
Direct Extrusion
(a) Direct extrusion to produce a hollow or semi‑hollow cross‑section; (b) hollow and (c) semi‑hollow cross‑ sections
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.
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Manufacturing Processes
Spring 2005
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
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Manufacturing Processes
Spring 2005
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).
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Manufacturing Processes
Spring 2005
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
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Manufacturing Processes
Spring 2005
Analysis of Extrusion
• Also called the reduction ratio, it is defined as
• 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
Extrusion Ratio
f
ox A
Ar
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Manufacturing Processes
Spring 2005
Analysis of Extrusion
The True Strain in Extrusion
For ideal deformation process:
The actual true strain is given by the following empirical equation:
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
xrln
xx rba ln
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Manufacturing Processes
Spring 2005
Analysis of Extrusion
Extrusion Pressure
For ideal deformation process:
For indirect extrusion
Where
xf rYp ln
xfYp
fY Is the average flow stress during deformation based on
ideal strain
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Manufacturing Processes
Spring 2005
Analysis of Extrusion
Extrusion Force and Power
The ram force in direct and indirect extrusion is simply given as
0pAF
The power required to carry out the extrusion operation is simply
FvP Where P= power in (J/s); F = ram force (N), and v = ram velocity (m/s)
Where F = ram force in extrusion (N), p = extrusion pressure (MPa), and A0 = billet area (mm2)
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Manufacturing Processes
Spring 2005
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)
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Manufacturing Processes
Spring 2005
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
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Manufacturing Processes
Spring 2005
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
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Manufacturing Processes
Spring 2005
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
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Manufacturing Processes
Spring 2005
Wire DrawingContinuous 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
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Manufacturing Processes
Spring 2005
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
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Manufacturing Processes
Spring 2005
Analysis of Drawing
Reduction RatioChange in size of work is usually given by area reduction:
o
fo
AAA
r
where r = area reduction in drawing;
Ao = original area of work (mm2) ; and
Af = final work (mm2)
DraftThe difference between original and final stock diameters
fo DDd Where d = draft (mm), Do = original diameter of work (mm), and
Df = final work diameter (mm).
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Manufacturing Processes
Spring 2005
Analysis of DrawingTrue Strain
If no friction occurred in drawing, true strain could be determined as follows:
rA
A
f
o
1
1lnln
f
off
A
AYY ln
Drawing StressThe stress that results from this ideal deformation is given by
Drawing ForceThe draw force is then the area of the drawing cross section multiplied by draw stress
fAF