ENM208 Bulk deformation Processes II ANADOLU U N I V E R S I T Y Industrial Engineering Department – Bulk Deformation Processes in Metal Forming – II 2006.

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

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

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.

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

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.

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

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).

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

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

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

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

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)

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)

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

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

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

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

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

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).

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