Metal forming

METAL FORMING THEORY AND
PRACTICE
Sheet Metal Forming Dr.K.BALASUNDARAM
Assistant Professor

Outline of Presentation
Sheet Metal Forming
Conventional processes- Explosive forming, electro-hydraulic
forming, magnetic pulse forming – Principles and process
parameters- Advantages- Limitations and Applications
Manufacturing Engineering 2

Basic of Manufacturing process
 In order to start, let us first understand what are the various basic
manufacturing processes?
 So, the basic manufacturing processes are 5 different types of basic
manufacturing processes.
 These manufacturing processes are Casting, Deformation processes
or Metal forming processes, Machining, Joining(fastening, welding and
adhesive joining), Finishing operation.

Casing Process
Deforming process
or
Metal forming
process

Machining
process

Joining Process Finishing Process
All these processes are used to convert a raw material into a final product,
we have certain raw material the material can be cast iron, it can be steel or
it can be any other form, it can be plastic, it can be any kind of wood. So,
any raw material is converted into the final product using any of these basic
processes.

Selection of Manufacturing Process
So, the job basically is to convert a raw material into the final product,
but the problem arise is that there are a number of a manufacturing
processes out of which we have to choose that, which manufacturing
process we should use to convert the raw material into the final
product.
So, selection of a manufacturing process to produce a product is a
trade off among a number of variables. So, what are these variables?
These variables are:
Materials, Shape ,
Size , Volume ,
complexity and other factors

Basic of Metal forming process
 Metal forming is one of the important manufacturing processes, as we
might have seen when we go to the market or we go to some manufacturing
industry.
 We see that the metal is being formed into different shape, as we do
sometimes if you take a hammer and start hitting a metal piece. We will, we
can see that under the impact of the hammer or the forces that we can apply
with the help of a hammer, the shape of the metal can be changed.
 So, the basic principle of metal forming is that by the application of
force, the metal is plastically deformed.

Metal forming processes
Metal Forming can be defined as the process in which the desired size
and shape of the object are obtained through plastic deformation of
material.
What are basically deformation processes?
Deformation processes exploit a remarkable property of metals, what is
this remarkable property which is their ability to flow plastically in the
solid state without deterioration of their properties?
10Msc- Manufacturing Engineering

Metal forming processes- Deformation processes
With the application of suitable pressure, the material is moved to obtain the
desired shape with almost no wastage, this is an important point to address in
case of deformation processes.
The required pressures are generally high and the tools and equipment
needed are quite expensive, large production quantities are often necessary to
justify the process.
As the metal is deformed into a useful shape, it experiences stresses such as
tension, compression, shear or various combinations.

Metal forming processes-Classification
Metal Forming
Sheet Metal workingBulk Deformation

Bulk Deformation
Bulk forming: It is a severe deformation process resulting in massive shape change. The
surface area-to-volume of the work is relatively small. Mostly done in hot working
conditions.
Bulk Forming
Extrusion processForging ProcessRolling Process
Wire and Bar
Drawing

Rolling: In this process, the workpiece in the form
of slab or plate is compressed between two rotating
rolls in the thickness direction, so that the thickness
is reduced. The rotating rolls draw the slab into the
gap and compresses it. The final product is in the
form of sheet.
Forging: The workpiece is compressed between two
dies containing shaped contours. The die shapes are
imparted into the final part.
Bulk Deformation

Extrusion: In this, the workpiece is compressed or
pushed into the die opening to take the shape of the
die hole as its cross section.
Wire or rod drawing: similar to extrusion, except
that the workpiece is pulled through the die opening
to take the cross-section
Bulk Deformation

 Sheet metal operations basically are very important in
manufacturing technology.
 Products that are made up of sheet metal like, some of the
examples are:
1. Sheet metal products can be metal desks.
2. Car bodies all of us travel in cars, all of us travel in busses,
trains. So, most of the parts or most of the bodies are made up
of sheet metal only.
3. Then the beverage can, all of us drink different cool drinks.
So, the cool drink cans are made up of sheet metal. So, sheet
metal products are all around us.
Sheet Metal Forming

Sheet Metal Forming
sheet metal forming is nothing new, it dates back to 5000 B.C when
house hold utensils and jewelry were made by hammering and
stamping gold, silver and copper.
Sheet Metal Working
Bending operation Stretching Deep Drawing Shearing Process

Bending: In this, the sheet material is strained by
punch to give a bend shape (angle shape) usually in a
straight axis.
Deep (or cup) drawing: In this operation, forming of
a flat metal sheet into a hollow or concave shape like
a cup, is performed by stretching the metal in some
regions. A blank-holder is used to clamp the blank on
the die, while the punch pushes into the sheet metal.
The sheet is drawn into the die hole taking the shape
of the cavity.
Sheet Metal Forming

Shearing: This is nothing but cutting
of sheets by shearing action.
Sheet Metal Forming

UNCONVENTIONAL
METAL FORMING
PROCESSES

UNCONVENTIONAL METAL FORMING PROCESSES
High Energy Rate Forming Processes
In these forming processes large
amount of energy is applied for a very
short interval of time.
The parts are formed at a rapid rate,
and thus these processes are also called
high – velocity forming processes.

There are several advantages of using these forming processes, are:
Die costs are low,
Easy maintenance of tolerances,
Possibility of forming most metals, and
Material does not show spring-back effect.
The production cost of components by such processes is low .
The limitation of these processes is the need for skilled personnel.

CLASSIFICATION
Metal Forming Processes
Electro Hydraulic Forming Magnetic FormingExplosive Forming

Explosive Forming
Explosive forming has evolved as one of the most dramatic of the new
metalworking techniques.
Explosive forming is the forming of sheet metal using explosive materials using
large amount of energy over a very short time.
Explosive forming, is distinguished from conventional forming in that the punch
or diaphragm is replaced by an explosive charge.

The explosives used are generally high – explosive chemicals, gaseous
mixtures, or propellants.
Explosive forming is employed in aerospace and aircraft industries and has
been successfully employed in the production of automotive-related components.
Explosive Forming
History of Explosive Forming
Explosive forming was applied in the 1960’s in the USA and for aeroplane
and space applications
Several factors contributed to the re-introduction of explosive forming in the
1990’s for forming products with more complicated shapes were required in
smaller

It is high velocity forming process
Explosion Shock Wave in
water
Kinetic
energy
Plastic
work
What is Explosive Forming ?

In this process the punch is replaced by an explosive charge
In Explosive Forming chemical energy from the explosives is used to generate shock
waves through a medium (mostly water), which are directed to deform the workpiece at
very high velocities.
The process has been successfully used to form steel plates 25 mm thick x 4 m diameter
and to bulge steel tubes as thick as 25 mm.
Explosives can be
Solid (TNT-trinitro toluene),
Liquid (Nitroglycerine),
Gaseous (oxygen and acetylene mixtures).
Explosive Forming

Explosive Forming – Process Description
 A die is manufactured according to the desired shape of the product. Dies can be made
from a number of materials including concrete, ductile iron, fibre glass and kirk site or
epoxy and concrete.
 Forming takes place inside a water tank or “explosion tank” where the die is placed.
The workpiece is situated directly above the die and explosive material placed above
that. The explosive material is typically Trinitro toluene (TNT), a mixture of acetylene
and oxygen or Nitroglycerine.
 Quite simply, when the explosive material is detonated, the resulting shock wave
through the transfer medium (the water) forces the workpiece material into the die, thus
assuming its shape

Explosive process
Figure Explosive forming 31

Explosive process-Sequence of operations
Figure Explosive forming: (1) setup, (2) explosive is detonated, and (3) shock wave forms part and plume
escapes water surface.

Types of explosive forming
Explosive Forming Operations can be divided into two groups, depending
on the position of the explosive charge relative to the workpiece.
Explosive Forming
Stand off Method Contact Method

Stand – off Method
An explosive is placed between the die
cavity and the work, a certain distance
from the work. This distance is called
the standoff distance.
Stand-off distance depends on the size
of the work, for larger parts it is usually
about half the diameter of the blank.
This high energy rate forming process
can be used to form big thick plates.

The Contact Method
The explosive can be placed directly on the work piece. Upon
detonation, explosive forces hit the work piece directly. This is called
the contact method.
The contact method uses an explosive charge directly in contact
with the workspace while detonation occurs.
The detonation can produce extremely high pressure on the surface
up to several million Psi (35000 Mpa)

The explosive charge in the form of cartridge is
held in direct contact with the work piece while the
detonation is initiated.
The detonation builds up extremely high
pressures (upto 30,000MPa) on the surface of he
work piece resulting in metal deformation, and
possible fracture.
The process is used often for bulging tubes, as
shown in fig .
The Contact Method

Stand – off Method Vs Contact Method

 Both ferrous and nonferrous metals including steel, aluminum, magnesium, and
their alloys.
 Some metal matrix composites like aluminum matrix, copper matrix and lead
matrix composites.
Materials for explosive forming
Quality Considerations
 Explosives contaminate the transfer media, which need to be cleaned each time
for better quality and process control.
 It is difficult to control the mechanical properties and dimensions of the part.

Cost saving since only of forming processes in one process
Used to form larger parts which can’t be easily pressed
Stimulates other kinds of forming processes in one process
The explosives used can be of any mass and shape, so the size of the product is not a
concern of matter
It can simulate a variety of other conventional metal forming techniques such as
stamp- or press-forming and spin-forming in a single operation
It is particularly suitable for short production runs of a large parts such as occurs in
aerospace applications.
It Maintains precise tolerances and Eliminates costly welds.
Explosive Forming - ADVANTAGES

High labor cost.
Suitable for low-quantity production.
Due to shock waves and spillage of water it is not suitable to carry out indoor.
It should be done in open air.
Applications
Some of the applications of explosive forming include:
•Sheet metal panels
•Tubing
•Housings
•Jet engine parts
•Missile nose cones
Ducts
Explosive Forming - DISADVANTAGES

APPLICATIONS BOILER PRODUCTS MISSILE PARTS
AIRCRAFT RADAR SHIELDS

History - Electro hydraulic Forming
The potential forming capabilities of submerged arc discharge processes were
recognized as early as the mid-1940s (Yutkin L.A.).
During the 1950s and early 1960s, the basic process was developed into production
systems. This work principally was by and for the aerospace industries.
By 1970, forming machines based on submerged arc discharge, were available from
machine tool builders. A few of the larger aerospace fabricators built machines of their
own design to meet specific part fabrication requirements.

ELECTROHYDRAULIC FORMING
Electro Hydraulic Forming is type of high energy rate forming processes
Electro hydraulic forming (EHF), also known as electro spark forming, is a
process in which electrical energy is converted into mechanical energy for the
forming of metallic parts.
The characteristics of this process are similar to those of explosive forming. The
major difference, is that a chemical explosive is replaced by a capacitor bank,
which stores the electrical energy.

A bank of capacitors is first charged to a high voltage and then discharged
across a gap between two electrodes, causing explosions inside the hollow
work piece, which is filled with some suitable medium, generally water
The deformation can be controlled by applying external restraints in the
form of die or by varying the amount of energy released.
ELECTROHYDRAULIC FORMING

Principle - ELECTROHYDRAULIC FORMING
A sudden electrical discharge in the form of sparks is produced between
electrodes and this discharge produces a shock wave in the water medium. This
shock wave deforms the work plate and collapses it into the die.
 The capacitor is charged through a charging circuit. When the switch is closed,
a spark is produced between electrodes and a shock wave or pressure pulse is
created. The energy released is much lesser than that released in explosive
forming.

Constructional Details and Working
A typical configuration of EHF includes a
 Discharge chamber
Electrodes
Forming die
Pulse generator which consists of a high-
voltage low-inductive bank of capacitors
C,
High-voltage/high current discharge
switch D, and
Charging/amplifying/rectifying circuit is
illustrated in Fig .

The capacitor bank is capable of producing discharges of 5–25 kV and
can store energies up to 100 kJ.
A sheet metal blank is placed on top of the discharge chamber.
A one-sided die is positioned above the blank.
After the air is evacuated from both sides of the blank, the chamber is filled with
water, fully immersing the electrodes.
After the voltage is applied to the electrodes, an electrical breakdown occurs
between the exposed tips of the electrodes which leads to the formation of a stable
plasma channel.
Constructional Details and Working

Process Parameters
Stand off distance : It must be optimum.
Capacitor used : The energy of the pressure pulse depends on the
size of capacitor.
Transfer medium : Usually water is used.
Materials formed and accuracy :All materials that can be formed by
conventional forming processes can be formed by EHF also. These materials are
aluminum alloys, nickel alloys.
External dimensions on tubular parts are possible to achieve within ± 0.05 mm
with the current state of technology

Safer in handling than the explosive materials.
More suitable if the work size is small to medium.
Thin plates can be formed with smaller amounts of energy.
The process does not depend on the electrical properties of the work material.
Only a single one-sided die is required
Extremely fast
Enables extremely deep forming (much more than is possible with conventional
stamping)
EHF can form hollow shapes with much ease and at less cost compared to other
forming techniques.
Advantages-Electro hydraulic Forming

Electro hydraulic Forming-Disadvantages
Suitable only for smaller works.
Need for vacuum makes the equipment more complicated.
Each discharge of the electrodes to create the high voltage discharge in the fluid
results in the formation of impurities in the water that results in vaporization of the
electrodes and may create surface defects in the surface of the part formed in the
process.
The fluid in the vessel generally must be drained and replaced for each tool cycle.
The volume of fluid in the vessel for a larger part tends to be fairly substantial and
a considerable portion of the cycle time of the tool is dedicated to draining and
refilling the vessel. 52Msc- Manufacturing Engineering

Electro hydraulic Forming-Applications
It include smaller radar dish, cone and other shapes in thinner and small works,
Reduction of capital investment for low volume aerospace applications,
In Automobile sector such as inside components of a passenger car door,
Miniature and fancy equipments having complicated profile for electronic
industry, etc.

Electro hydraulic Forming-Applications

ELECTROMAGNETIC FORMING
Electromagnetic forming is a high strain rate forming process used for shaping
metals
Electromagnetic forming (EMF) is a high-speed forming method also called
impulse forming process.
The electromagnetic forming (EMF) process is one of the most common
high rate techniques. The source of energy used to deform the metal is an
electrical discharge.
This process is primarily used for three forming operations, namely, sheet
metal forming, tube expansion, and tube compression.

The EMF technology is based on the utilization of current driven electromagnetic forces
acting on the workpiece.
 The force application is contact free and no working media or lubrication is required, so
that any disturbance of the surface due to wear is avoided and the cleaning effort during
production is minimized.
Initially the charged capacitors discharge pulses of oscillating current through the coil.
Due to this, the magnetic field produced by the coil varies proportionately.
According to Faraday’s law of electromagnetic induction, this charging magnetic field
induces an electromotive force in the work piece.

The EMF process uses a capacitor bank, a forming coil, a field shaper, and an
electrically conductive workpiece to create intense magnetic fields that are used to
do the useful work.
The resulting eddy currents that are induced in a conductive workpiece that
is placed close to the coil then interact with the magnetic field to cause mutual
repulsion between the workpiece and the forming coil.
The force of this repulsion is sufficient to stress the work metal beyond its
yield strength, resulting in a permanent deformation

Principle of Electromagnetic Forming
To illustrate the principle of electromagnetic forming, consider a tubular work
piece.
This work piece is placed in or near a coil, as shown in Fig.
A high charging voltage is supplied for a short time to a bank of capacitors
connected in parallel. (The amount of electrical energy stored in the bank can be
increased either by adding capacitors to the bank or by increasing the voltage).
When the charging is complete, which takes very little time, a high voltage switch
triggers the stored electrical energy through the coil.

A high - intensity magnetic field is established which induces eddy currents into
the conductive work piece, resulting in the establishment of another magnetic field.
The forces produced by the two magnetic fields oppose each other with the
consequence that there is a repelling force between the coil and the tubular work
piece that causes permanent deformation of the work piece.
In electromagnetic forming, the initial gap between the work piece and the die
surface, called the fly distance, must be sufficient to permit the material to deform
plastically.
Principle of Electromagnetic Forming

Formation methods
Electromagnetic formation can usually be applied to three forming methods . They are :
1. Compression, 2. Expansion, and 3. Counter forming
In principle the three major process variants
Electromagnetic compression of tubes or hollow profiles by a typically cylindrical coil
surrounding the workpiece,
Electromagnetic expansion of tubes or hollow profiles by a typically cylindrical coil
positioned inside the workpiece, and
Electromagnetic forming of flat of three-dimensionally preformed sheets by an
accordingly shaped coil are differentiated.

The three method as shown in figure
(a) A tubular workpiece is compressed by an
external coil, usually against a grooved
contoured insert, plug, tube or fitting inside
the workpiece.
(b) A tubular workpiece is expanded by an
internal coil as shown in figure(b) usually
against a collar or other component
surrounding the workpiece .
(c)Flat stock is almost always contour-formed
against a die as seen in figure (c).
Formation methods
(a) Compression, (b) Expansion. (c) Contour forming

Electromagnetic Forming Process Parameters
 Workpiece thickness
A higher thickness means that the magnetic field diffuses slower through the
workpiece wall.
 Electrical conductivity
The higher the electrical conductivity of the workpiece, the better the
shielding of the magnetic field, the pressure difference in higher.
 Frequency
A higher frequency of the discharged current can balance a low conductivity
or a small wall thickness.

 Gap between workpiece and tool coil
The smaller the air gap, higher is magnetic field and pressure.
 Winding of the tool coil
For each pulse generator and each forming task exists an optimum of
number of turns.
Electromagnetic Forming Process Parameters

Electromagnetic Forming -Die materials
 The die used in electromagnetic process should be made of low electrical
conductivity to minimize the magnetic cushion effect.
 Dies are generally made of the following materials: Steel or epoxy resin. Steel
dies have longer life but the disadvantage of steel dies is that magnetic cushion
effect is not entirely prevented.
 Air is often evacuated from the die to ensure good reproduction of detail, and
prevent distortion caused by entrapped air, which is particularly likely to occur
with thin gauge material.

Electromagnetic Forming -Advantages
 Suitable for small tubes
 Operations like collapsing, bending and crimping can be easily done.
 Electrical energy applied can be precisely controlled and hence the
process is accurately controlled.
 The process is safer compared to explosive forming.
 Wide range of applications.

Electromagnetic Forming - Disadvantages
 Applicable only for electrically conducting materials.
 Not suitable for large work pieces.
 Rigid clamping of primary coil is critical.
 Shorter life of the coil due to large forces acting on it

Electromagnetic Forming -Applications
• Electromagnetic forming process is capable of a wide variety of forming
and assembly operations.
• Crimping of coils, tubes, wires
• Bending of tubes into complex shapes
• Bulging of thin tubes.
• It has found extensive applications in the fabrication of hollow, non –
circular, or asymmetrical shapes from tubular stock.

•Flat coils have been used on flat sheets to produce stretch
(internal) and shrink (external) flanges on ring and disc – shaped
work pieces.
•Electromagnetic forming has also been used to perform shearing,
piercing, and reverting.
Electromagnetic Forming -Applications

Metal forming

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