-
ll EaI svaamaI samaqa- ll
aa EaI svaamaI samaqa- aa [email protected]
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Unit.1 AMP
METAL FORMING
Contents :
1.Roll forming
2.High velocity hydro forming,
3.High velocity Mechanical Forming,
4.Electromagnetic forming,
5.High Energy Rate forming (HERF),
6.Spinning,
7.Flow forming,
8.Shear Spinning
1. Roll Forming
Rolling is the most extensively used metal forming process and
its share is roughly
90% process.
The material to be rolled is drawn by means of friction into the
two revolving roll
gap.
The compressive forces applied by the rolls reduce the thickness
of the material or
changes its cross sectional thickness of the material .
The geometry of the product depend on the contour of the roll
gap.
Roll materials are cast iron, cast steel and forged steel
because of high strength and
wear resistance.
Hot rolls are generally rough so that they can bite the work,
and cold rolls are
ground and polished for good finish.
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In rolling the crystals get elongated in the rolling direction.
In cold rolling crystal
more or less retain the elongated shape but in hot rolling they
start reforming after
coming out from the deformation on zone .
The peripheral velocity of rolls at entry exceeds that of the
strip, which is dragged
in if the interface friction is high strip.
In the deformation zone the thickness of the strip gets reduced
and it elongates. This
increases the linear speed of the at the exit.
Thus there exist a neutral point where roll speed and strip
speeds are equal. At this
point the direction of the friction speeds are equal.
When the angle of contact exceeds the friction angle the rolls
cannot draw
fresh strip
Roll torque, power etc. increase with increase in roll work
contact length or roll
radius.
Rolling is a deformation process in which the thickness of the
work is reduced by compressive
forces exerted by two opposing rolls. The rolls rotate as
illustrated in Figure 1. to pull and
simultaneously squeeze the work between them. The basic process
shown in our figure 1. is flat
rolling, used to reduce the thickness of a rectangular cross
section. A closely related process is
shape rolling, in which a square cross section is formed into a
shape such as an I-beam. Most
rolling processes are very capital intensive, requiring massive
pieces of equipment, called rolling
mills, to perform them. The high investment cost requires the
mills to be used for production in
large quantities of standard items such as sheets and plates.
Most rolling is carried out by hot
working, called hot rolling, owing to the large amount of
deformation required. Hot-rolled metal
is generally free of residual stresses, and its properties are
isotropic. Disadvantages of hot rolling
are that the product cannot be held to close tolerances, and the
surface has a characteristic oxide
scale. Steel making provides the most common application of
rolling mill operations. Let us follow
the sequence of steps in a steel rolling mill to illustrate the
variety of products made. Similar steps
occur in other basic metal industries. The work starts out as a
cast steel ingot that has just solidified.
While it is still hot, the ingot is placed in a furnace where it
remains for many hours until it has
reached a uniform temperature throughout, so that the metal will
flow consistently during rolling.
For steel, the desired temperature for rolling is around 1200 C
(2200F). The heating operation is
called soaking, and the furnaces in which it is carried out are
called soaking pits.
From soaking, the ingot is moved to the rolling mill, where it
is rolled into one of three intermediate
shapes called blooms, billets, or slabs. Abloom has a square
cross section 150 mm
150 mm (6 in 6 in) or larger. A slab
is rolled from an ingot or a bloom and has a rectangular cross
section of width 250 mm (10 in) or
more and thickness 40 mm (1.5 in) or more. A billet is rolled
from a bloom and is square with
dimensions 40 mm (1.5 in) on a side or larger. These
intermediate shapes are subsequently rolled
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into final product shapes. Blooms are rolled into structural
shapes and rails for railroad tracks.
Billets are rolled into bars and rods. These shapes are the raw
materials for machining, wire
drawing, forging, and other metalworking processes. Slabs are
rolled into plates, sheets, and strips.
Hot-rolled plates are used in shipbuilding, bridges, boilers,
welded structures for various heavy
machines, tubes and pipes, and many other products. Figure 3.
shows some of these rolled steel
products. Further flattening of hot-rolled plates and sheets is
often accomplished by cold rolling,
in order to prepare them for subsequent sheet metal operations.
Cold rolling strengthens the metal
and permits a tighter tolerance on thickness. In addition, the
surface of the cold-rolled sheet is
absent of scale and generally superior to the corresponding
hot-rolled product. These
characteristics make cold-rolled sheets, strips, and coils ideal
for stampings, exterior panels, and
other parts of products ranging from automobiles to appliances
and office furniture.
Fig.3.0 Rolling Process
Roll forming is one of the most common techniques used in the
forming process, to obtain a
product as per the desired shape. The roll forming process is
mainly used due to its ease to be
formed into useful shapes from tubes, rods, and sheets. In this
process, sheet metal, tubes, strips
are fed between successive pairs of rolls, that progressively
bent and formed, until the desired
shape and cross section are attained. The roll forming process
adds strength and rigidity to
lightweight materials, such as aluminum, brass, copper and zinc,
composites, some heavier ferrous
metals, specialized alloys and other exotic metals (Anne Marie
Habrken 2007). Roll forming
processes are successfully used for materials that are difficult
to form by other conventional
methods because of the spring back, as this process achieves
plastic deformation without the
spring back. In addition, the roll forming improves the
mechanical properties of the material,
especially, its hardness, grain size, and also increases the
corrosion rate. The deformation
behavior plays an important role to achieve dimensional accuracy
of the roll formed parts. The
purpose of conducting this roll forming process is to compare
the results with those of
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electromagnetic tube compression forming, through experiments
and simulations using the finite
element analysis.
FLAT ROLLING AND ITS ANALYSIS
Flat rolling is illustrated in Figures 3.0 and .3.1. It involves
the rolling of slabs, strips, sheets, and
platesworkparts of rectangular cross section in which the width
is greater than the thickness. In
flat rolling, the work is squeezed between two rolls so that its
thickness is reduced by an amount
called the draft.
Draft is sometimes expressed as a fraction of the starting stock
thickness, called the reduction.
In addition to thickness reduction, rolling usually increases
work width. This is called spreading
and it tends to be most pronounced with low width-to-thickness
ratios and low coefficients of
friction.
Fig3.1.Some of the steel products made in a rolling mill.
Rolling is the most widely used forming process, which produces
products like bloom, billet, slab,
plate, strip, sheet, etc. In order to increase the owability of
the metal during rolling, the process
is generally performed at high temperature and consequently the
load requirement reduces.
Friction plays an important role in rolling as it always opposes
relative move- ment between two
surfaces sliding against each other. At the point where
workpiece enters the roll gap, the surface
speed of the rolls is higher than that of the workpiece. So, the
direction of friction is in the direction
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of the workpiece movement and this friction force drags it into
the roll gap. During rolling, velocity
of the workpiece increases as material ow rate remains same all
throughout the deformation.
Material velocity is equal to the surface speed of the rolls at
a plane, called the neutral plane. In
order to make the analysis of at rolling process simple,
assumptions like plane strain deformation,
volume constancy principle, constant coefcient of friction,
constant surface velocity of the rolls,
etc., are considered. Out of all varieties of the rolling
processes, the at rolling is the most practical
one which produces around 4060 % of the total rolled
products.
2. High Velocity Hydro Forming
In hydroforming, high viscous uid is used to deform the metal
against the complex shaped die.
Since no punch is used in this method, hence, thinning of the
sheet metal at the punch corner does
not occur. Hydroforming is of two types; sheet forming and tube
forming. Till date, there is no
published research work available on sheet hydroforming of
TFSWBs. However, Yuan et al.
performed hydro- forming of tubes, which were fabricated from
the at sheets by FSW and further
undergone post-weld heat treatment. Nowadays, this method is
used to manufacture aircrafts
tubular components.
In hydroforming, fluid pressure acting over a flexible membrane
is utilized for
controlling the metal flow. Fluid pressure upto 100 MPa is
applied. The fluid pressure on
the membrane forces the sheet metal against the punch more
effectively. Complex shapes
can be formed by this process. In tube hydroforming, tubes are
bent and pressurized by high
pressure fluid. Rubber forming is used in aircraft industry.
1.Tube Hydro forming :
Used when a complex shape is needed
A section of cold-rolled steel tubing is placed in a closed die
set
A pressurized fluid is introduced into the ends of the tube
The tube is reshaped to the confine of the cavity
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2. SHEET HYDROFORMING
1.Sheet steel is forced into a female cavity by water under
pressure from a pump or by press
action.
2.Sheet steel is deformed by a male punch, which acts against
the fluid under pressure.
Fig. Tube hydro forming
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Fig .Sheet hydro forming
APPLICATIONS Automotive industry,
Aerospace-Lighter, stiffer parts
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ADVANTAGES
Weight reduction .
Improved structural strength and stiffness.
Lower tooling cost due to fewer parts.
Fewer secondary operations (no welding of sections required and
holes may be punched
during hydroforming)
Tight dimensional tolerances and low spring back.
Reduced scrap.
Disadvantages
Slow cycle time.
Expensive equipment and lack of extensive knowledge base for
process and tool design .
Requires new welding techniques for assembly.
3.Electromagnetic Forming
It is a type of high velocity cold forming process for
electrically conductive metals most commonly
copper and aluminium
The process is also called magnetic pulse forming, and is mainly
used for swaging type
operations, such as fastening fittings on the ends of tubes and
crimping the terminal ends of cables.
Other applications of the process are blanking, forming,
embossing, and drawing. The work
coils needed for different applications may vary although the
same power source is be used.
The principle of electromagnetic forming of a tubular work piece
is shown in Figure.1.4.
The work piece is placed into or enveloping a coil. 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 (nptel).Either permanent or
expandable coils may be used. Since
the repelling force acts on the coil as well the work, the coil
itself and the insulation on it
must be capable of withstanding the force, or else they will be
destroyed. The expandable coils
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are less costly, and are also preferred when a high energy level
is needed (Daehn Glenn 1999).
Electro Magnetic forming can be accomplished in any of the
following three types of coils
used, depending upon the operation and requirements.
Figure 1.4 Various applications of electromagnetic forming
process (nptel). (i) Compression (ii)
Expansion and (iii) Sheet metal forming.
A coil used for ring compression is shown in Figure 1.4. (i)
This coil is similar in geometry
to an expansion coil. However, during the forming operation, the
coil is placed
surrounding the tube to be compressed.
A coil used for tube expansion is shown in Figure 1.4. (ii); for
an expansion operation, the
coil is placed inside the tube to be expanded.
A flat coil which consists of a metal strip wound spirally in a
plane is shown in Figure 1.4.
(iii); Coils of this type are used for forming of sheet
metal.
Two types of deformations can be obtained generally in
electromagnetic forming system:
(i) compression (shrinking) and (ii) expansion (bulging) of
hollow circular cylindrical
work pieces. When the work piece is placed inside the forming
coil, it is subjected to
compression (shrinking) and its diameter decreases during the
deformation process. When
the work piece is placed outside the forming coil, it is
subjected to expansion (bulging)
and its diameter increases during the deformation process.
Either compression, or
expansion, and even a combination of both to attain final shapes
can be obtained,
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with a typical electromagnetic forming system for shaping hollow
cylindrical objects. In
order to get more insight into the electromagnetic forming
process that can lead to
such shapes, an investigation is required of the electromagnetic
forming of hollow circular
cylindrical objects in detail.
The electromagnetic forming technology has unique advantages in
the forming, joining
and assembly of light weight metals such as aluminum because of
the improved
formability and mechanical properties, strain distribution,
reduction in wrinkling, active
control of spring back, minimization of distortions at local
features, local coining and
simple die (Daehn et al 2003, Kamal 2005 and Seth et al 2005).
The applications of
electromagnetic tube compression include, shape joints between a
metallic tube and an
internal metallic mandrel for axial or torsional loading,
friction joints between a
metallic tube and a wire rope or a non-metallic internal
mandrel, solid state welding
between a tube and an internal mandrel of dissimilar metallic
materials, tow poles,
aircraft torque tubes, chassis components and dynamic compaction
of many kinds of
powders (Chelluri 1994 and Mamlis et al 2004).
Some important features of electromagnetic forming
Some important characteristic process features that make the
electromagnetic forming
different from other forming processes are:
(1) Sheet metal in electromagnetic forming must be conductive
enough to allow the
sufficient induced eddy currents. The efficiency of
electromagnetic forming is directly related to
the conductivity of the metal sheet. Metals with poor
conductivity can only be formed effectively
if an auxiliary driver sheet with high conductivity is used to
push the metal sheet (George
Dieter 1986 and Richard Gedney 2002). Aluminum alloys are good
electrical conductors with
higher conductivity compared to plain carbon steel (Lee and Huh
1997). Aluminum alloys are
generally suitable for electromagnetic forming.
(2) The discharge time of electromagnetic forming is very short,
generally very short in the
order of 10 microseconds (Vincent Vohnout 1998). The
conventional sheet stamping usually takes
a few seconds. The current in coil and sheet metal are damped
sinusoidally, and the most
deformation work is done within the first half cycle. Therefore,
electromagnetic forming is a
transient event compared with conventional sheet stamping.
Benefits of electromagnetic forming
Electromagnetic forming usually is used to accelerate the sheet
metal at velocities up to a
few hundred meters per second, which are 100 to 1000 times
greater than the deformation rates of
conventional quasi-static forming such as the sheet metal
stamping (~0.1m/s to ~100m/s). It is well
known that high deformation velocity (over about 50m/s) can
significantly increase the formability
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of metals by several times, compared with those obtained in
conventional quasi-static forming
(Glenn et al 1999 and Amit et al 1996). The extended formability
is available over a broad range
of deformation velocities, which is kind of material dependent
but generally lies over 50m/s (Glenn
et al1999).
A complete understanding of how formability is affected by high
deformation velocity is
still lacking. However, some issues about the improvement of
formability are clear now and will
be briefly discussed. The effect of inertia on a neck is the
most straightforward way to explain the
improved formability in high velocity forming. Several
researchers have shown that failure in a
tensile sample is delayed when inertial forces are relatively
large (X.Hu and Glenn 1996). Hu and
Daehn believed that the velocity gradient in the necking area
leads to non-uniform inertia forces.
Further the inertia forces produce the additional tensile stress
and strain at the areas outside of
necking. The second reason for improved formability is due to
inertial ironing. The sheet
metal with high velocity impacts the stationary hard die, and
produces a very large through-
thickness compressive stress. This is termed as inertial ironing
(Glenn et al 1999). This
compressive stress can be much larger than the flow stress of
the metal, and produced significal
effect on the deformation modes. There are some other issues on
the formability in high velocity
forming, such as boundary conditions, constitutive equation
changes at high velocity.
The EMF process has several advantages over conventional forming
processes. Some of
these advantages are common to all the high rate processes while
some are unique to
electromagnetic forming. The advantages include:
1.Improved formability.
2.Wrinkling can be greatly eliminated.
3.Forming process can be combined with joining and assembling
even with the dissimilar
components including glass, plastic, composites and other
metals.
4.Close dimensional tolerances are possible as spring back can
be significantly reduced.
5.Use of single sided dies reduces the tooling costs.
6.Applications of lubricants are greatly reduced or even
unnecessary; so, forming can be
used in clean room conditions.
7. The process provides better reproducibility, as the current
passing through the forming coils is
the only variable need to be controlled for a given forming
set-up. This is controlled by the amount
of energy discharged.
8.Since there is no physical contact between the work piece and
die as compared to the use of a
punch in conventional forming process, the surface finish can be
improved.
9. High production rates are possible. The attribute that
essentially control the production
rate would be the time taken for the capacitor bank to get
charged.
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10. It is an environmentally clean process as no lubricants are
necessary.
As mentioned before, the distribution of electromagnetic
pressure can be directly
controlled by the spatial configuration of the coil. The
magnitude of electromagnetic pressure can
be controlled by the stored charge in the capacitor bank.
Electromagnetic forming is easy to apply and control, making it
very suitable to be combined
with conventional sheet stamping. The practical coil can be
designed to deal with the different
requirements of each forming operation.
Actual Process
The electrical energy stored in a capacitor bank is used to
produce opposing magnetic fields
around a tubular work piece, surrounded by current carrying
coils. The coil is firmly held
and hence the work piece collapses into the die cavity due to
magnetic repelling force, thus
assuming die shape.
Fig. Electro Magnetic Forming
Process details/ Steps:
i) The electrical energy is stored in the capacitor bank
ii) The tubular work piece is mounted on a mandrel having the
die cavity to produce shape on
the tube.
iii) A primary coil is placed around the tube and mandrel
assembly.
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iv) When the switch is closed, the energy is discharged through
the coil v) The coil produces a
varying magnetic field around it.
vi) In the tube a secondary current is induced, which creates
its own magnetic field in the
opposite direction.
vii) The directions of these two magnetic fields oppose one
another and hence the rigidly held
coil repels the work into the die cavity.
viii) The work tube collapses into the die, assuming its
shape.
Process parameters:
i) Work piece size
ii) Electrical conductivity of the work material.
iii) Size of the capacitor bank
iv) The strength of the current, which decides the strength of
the magnetic field and the force
applied.
v) Insulation on the coil. vi) Rigidity of the coil.
Advantages:
i) Suitable for small tubes
ii) Operations like collapsing, bending and crimping can be
easily done.
iii) Electrical energy applied can be precisely controlled and
hence the process is accurately
controlled.
iv) The process is safer compared to explosive forming.
v) Wide range of applications.
Limitations:
i) Applicable only for electrically conducting materials.
ii) Not suitable for large work pieces.
iii) Rigid clamping of primary coil is critical.
iv) Shorter life of the coil due to large forces acting on
it.
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Applications:
i) Crimping of coils, tubes, wires
ii) Bending of tubes into complex shapes.
iii) Bulging of thin tubes.
4. High Energy Rate Forming (HERF)
Introduction:
All modern manufacturing industries focus on a higher economy,
increased productivity
and enhanced quality in their manufacturing processes. To
enhance the material performance, a
high energy rate forming technique is of great importance to
industry, which relies on a long and
trouble free forming process.
High energy rate forming (HERF) is the shaping of materials by
rapidly conveying
energy to them for short time durations. There are a number of
methods of HERF, based mainly
on the source of energy used for obtaining high velocities
(Wilson Frank 1964). Common methods
of HERF are explosive forming, electro hydraulic forming (EHF)
and electromagnetic forming
(EMF). Among these techniques, electromagnetic forming is a
high-speed process, using a pulsed
magnetic field to form the work piece, made of metals such as
copper and aluminum alloys with
high electrical conductivity, which results in increased
deformation, higher hardness, reduced
corrosion rate and good formability. Reduction of weight is one
of the major concerns in
the automotive industry. Aluminium and its alloys have a wide
range of applications, especially in
the fabrication industries, aerospace, automobile and other
structural applications, due to their low
density and high strength to weight ratio, higher ductility and
good corrosive resistance.
High energy rate forming methods are gaining popularity due to
the various advantages
associated with them. They overcome the limitations of
conventional forming and make it possible
to form metals with low formability into complex shapes. This,
in turn, has high economic and
environmental advantages linked due to potential weight savings
in vehicles (Wilson Frank 1964).
In conventional forming conditions, inertia is neglected, as the
velocity of forming is typically less
than 5 m/s, while typical high velocity forming operations are
carried out at work-piece velocities
of about 100 m/s (Daehn Glenn 2003).
In this process the high energy released due to explosion of an
explosive is utilized for
forming of sheets. No punch is required. A hollow die is used.
The sheet metal is clamped
on the top of the die and the cavity beneath the sheet is
evacuated. The assembly is placed
inside a tank filled with water. An explosive material fixed at
a distance from the die is
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then ignited. The explosion causes shock waves to be generated.
The peak pressure
developed in the shock wave is given by:
p = k( /R)a
k is a constant, a is also a constant. R is the stand-off
distance. Compressibility of the
medium and its impedance play an important role on peak
pressure. If the compressibility
of the medium used is lower, then the peak pressure is higher.
If the density of the
medium is higher, the peak pressure of the shock wave is higher.
Detonation speeds as
high as 6500 m/s are common. The metal flow is also happening at
higherspeed, namely,
at 200 m/s. Strain rates are very high. Materials which do not
loose ductility at higher
strain rates can be explosively formed. The stand off distance
also determines the peak
pressure during explosive forming. Steel plates upto 25 mm
thickness are explosive
formed.
Tubes can be bulged using explosive forming.
Fig. : Explosive Forming
The forming processes are affected by the rates of strain used.
Effects of strain rates during
forming:
1. The flow stress increases with strain rates
2. The temperature of work is increases due to adiabatic
heating.
3. Improved lubrication if lubricating film is maintained.
4. Many difficult to form materials like Titanium and Tungsten
alloys, can be deformed under
high strain rates.
Principle / important features of HERF processes:
The energy of deformation is delivered at a much higher rate
than in conventional practice.
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Larger energy is applied for a very short interval of time.
High particle velocities are produced in contrast with
conventional forming process.
The velocity of deformation is also very large and hence these
are also called High Velocity
Forming (HVF) processes.
Many metals tend to deform more readily under extra fast
application of force.
Large parts can be easily formed by this technique.
For many metals, the elongation to fracture increases with
strain rate beyond the usual metal
working range, until a critical strain rate is achieved, where
the ductility drops sharply.
The strain rate dependence of strength increases with increasing
temperature.
The yield stress and flow stress at lower plastic strains are
more dependent on strain rate than
the tensile strength.
High rates of strain cause the yield point to appear in tests on
low carbon steel that do not show
a yield point under ordinary rates of strain.
Advantages of HERF Processes
i) Production rates are higher, as parts are made at a rapid
rate. ii) Die costs are relatively
lower.
iii) Tolerances can be easily maintained.
iv) Versatility of the process it is possible to form most
metals including difficult to form
metals.
v) No or minimum spring back effect on the material after the
process.
vi) Production cost is low as power hammer (or press) is
eliminated in the process. Hence it is
economically justifiable.
vii) Complex shapes / profiles can be made much easily, as
compared to conventional forming.
viii) The required final shape/ dimensions are obtained in one
stroke (or step), thus eliminating
intermediate forming steps and pre forming dies.
ix) Suitable for a range of production volume such as small
numbers, batches or mass
production.
Limitations:
i) Highly skilled personnel are required from design to
execution. ii) Transient stresses of high
magnitude are applied on the work. iii) Not suitable to highly
brittle materials
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iv) Source of energy (chemical explosive or electrical) must be
handled carefully. v)
Governmental regulations/ procedures / safety norms must be
followed.
vi) Dies need to be much bigger to withstand high energy rates
and shocks and to prevent
cracking.
vii) Controlling the application of energy is critical as it may
crack the die or work.
viii) It is very essential to know the behavior or established
performance of the work metal
initially.
Applications:
i) In ship building to form large plates / parts (up to 25 mm
thick). ii) Bending thick tubes/
pipes (up to 25 mm thick).
iii) Crimping of metal strips. iv) Radar dishes
v) Elliptical domes used in space applications.
vi) Cladding of two large plates of dissimilar metals
5. Spinining
Spinning, in conventional terms, is defined as a process whereby
the diameter of the blank is
deliberately reduced either over the whole length or in defined
areas without a change in the wall
thickness.
METAL SPINNING is a term used to describe the forming of metal
into seamless,
axisym- metric shapes by a combination of rotational motion and
force . Metal spinning typically
involves the forming of axisymmetric components over a rotating
mandrel using rigid tools or
rollers. There are three types of metal- spinning techniques
that are practiced: manual
(conventional) spinning , power spin- ning , and tube spinning .
The rst two of these techniques
are described in this article. Tube-spinning technology is de-
scribed in the articles Flow
Forming and Roll Forming of Axially Symmetric Components in
Metalworking: Bulk
Forming,
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Operation.
Fig.Spinning Setup
In manual spinning, a circular blank of a at sheet, or preform,
is pressed against a rotating
mandrel using a rigid tool . The tool is moved either manually
or hydraulically over the mandrel
to form the component, as shown in Fig. 5.1. The forming
operation can be performed using several
passes. Manual metal spinning is typically performed at room
temperature. However, elevated-
temperature metal spinning is performed for components with
thick sections or for alloys
with low ductility. Typical shapes that can be formed using
manual metal spinning are
shown in Fig. 5.2 and 5.3; these shapes are difcult to form
economically using other techniques.
Manual spinning is only economical for low-volume production .It
is extensively used for
prototypes or for production runs of less than ~1000 pieces,
because of the low tooling costs.
Larger volumes can usually be produced at lower cost by power
spinning or press forming.
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Fig. a. Schematic diagram of the manual metal- spinning process,
showing the deformation of a
metal disk over a mandrel to form a cone
Various components produced by metal spinning
_ Bases, baskets, basins, and bowls
_ Bottoms for tanks, hoppers, and kettles
_ Housings for blowers, fans, filters, and flywheels
_ Ladles, nozzles, orifices, and tank outlets
_ pans, and pontoons
_ Cones, covers, and cups
_ Cylinders and drums
_ Funnels
_ Domes, hemispheres, and shells
_ Rings, spun tubing,
_ Vents, venturis, and fan wheels
Fig. b. Typical components that can be produced by manual metal
spinning. Conical, cylindrical,
and dome shapes are shown. Some product examples include bells,
tank ends, funnels, caps,
aluminum kitchen utensils, and light reectors
Manual Spinning of Metallic Components
Manual metal spinning is practiced by pressing a tool against a
circular metal preform
that is rotated using a lathe-type spinning machine. The tool
typically has a work face that is
rounded and hardened. Some of the traditional tools are given
curious names that describe their
shape, such as sheeps nose and ducks bill. The rst manual
spinning machine was
developed in the 1930s. Manual metal spinning involves no
signicant thinning of the work metal;
it is essentially a shaping technique. Metal spinning can be
performed with or without a forming
mandrel. The sheet preform is usually deformed over a mandrel of
a predetermined shape,
but simple shapes can be spun without a mandrel. Various
mechanical devices and/or levers are
typically used to increase the force that can be applied to the
preform. Most ductile metals and
alloys can be formed using metal spinning. Manual metal spinning
is generally performed without
heating the workpiece; the preform can also be preheated to
increase ductility and/or reduce the
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ow stress and thereby allow thicker sections to be formed.
Manual metal spinning is used to form
cups, cones, anges, rolled rims, and double-curved surfaces of
revolution (such as bells).
Typical shapes that can be formed by manual metal spinning are
shown in Fig. 3 and 4; these
shapes include components such as light reectors, tank ends,
covers, housings, shields, and
components for musical instruments.
Fig. 5.3 Photograph of conical components that were produced by
metal spinning. Courtesy of Leifeld USA Metal
Spinning, Inc.
ADVANTAGES
4. The tooling costs and investment in capital equipment are
relatively small (typically,
at least an order of magnitude less than a typical forging press
that can effect the
same operation).
5. The setup time is shorter than for forging.
6. The design changes in the workpiece can be made at relatively
low cost.
DISADVANTAGES
Highly skilled operators are required, because the uniformity of
the formed part
depends to a large degree on the skill of the operator.
Manual metal spinning is usually signicantly slower than press
forming.
The deformation loads available are much lower in manual metal
spinning than in
press forming.
6. Flow Forming
Flow forming is a modernized, improved advanced version of metal
spinning, which is
one of the oldest methods of chipless forming. Flow forming has
spread widely since 1950. The
metal spinning method used a pi- voted pointer to manually push
a metal sheet mounted at one end
of a spinning mandrel. This method was used to fabricate
axisymmetric, thinwalled, lightweight
domestic products such as saucepans and cooking pots.
Flow forming is a process whereby a metal blank, a disc or a
hollow tube are mounted on a mandrel
which rotates the material to make flow axially by one or more
rollers along the rotating mandrel.
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The major difference between spinning and flow forming is, in
spinning, the thickness reduction
is very minor and in flow forming the variation in thickness can
be maintained at different places along
axial directions.
Flow forming means shaping a product of sheet metal, tube or
drawpiece in one are more
passes of the forming roll or rolls. The magnitude of wall
thinning depends on the properties of
the input material and the number of passes.
Flow Forming is an incremental metal forming technique in which
a disk or tube of metal
is formed over a mandrel by one or more rollers using tremendous
pressure. The roller deforms
the workpiece, forcing it against the mandrel, both axially
lengthening and radially thinning it.
Since the pressure exerted by the roller is highly localized and
the material is incrementally formed,
often there is a net savings in energy in forming over drawing
processes. Flow forming subjects
the workpiece to a great deal of friction and deformation. These
two factors may heat the
workpiece to several hundred degrees if proper cooling fluid is
not utilized. Flow forming is often
used to manufacture automobile wheels.
During flow forming, the workpiece is cold worked, changing its
mechanical properties,
so its strength becomes similar to that of forged metal.Flow
forming, also known as tube spinning,
is one of the techniques closely allied to shear forming.
The two types of flow forming are shown in Fig. a..
schematically. The difference is according to
the direction of material flow with respect to direction of
motion of tool (roller). If both are in same
direction, then it is forward flow forming and if they are in
opposite direction, then it is backward flow
forming. Forward flow forming is suitable for long, high
precision thin walled components. Backward
flow forming is suitable for blanks without base or internal
flange. In forward spinning the roller
moves away from the fixed end of the work piece, and the work
metal flows in the same direction as the
roller, usually toward the headstock. The main advantage in
forward spinning as compared to backward
spinning is that forward spinning will overcome the problem of
distortion like bell-mouthing at the free end
of the blank and loss of straightness. In forward spinning
closer control of length is possible because as
metal is formed under the rollers it is not required to move
again and any variation caused by the variable
wall thickness of the per- form is continually pushed a head of
rollers, eventually be- coming trim metal
beyond the finished length. The disadvantage of forward flow
forming is that the Production is slower in
forward spinning because the roller must transverse the finished
length of the work piece. In backward
flow forming the mandrel is unsupported. In backward spinning
the work piece is held against a fixture
on the head stock, the roller advances towards the fixed end of
the work piece, work flows in the opposite
direction. The advantage of backward flow forming over forward
flow forming:
1. The preform is simpler for backward spinning because it
slides over the mandrel and does not
require an internal flange for clamping.
2. The roller transverse only 50% of the length of the fi-
nished tube in making a reduction of
50% wall thickness and only 25% of the final, for a 75%
reduction. We can procedure 3 m
length tube by using of mandrel.
3. In both the flow forming processes, there is no difference in
stress and strain rate.
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The major disadvantage of backward tube spin- ning is that
backward flow forming is normally prone
to non uniform dimension across the length of the product
In this Process as shown in Fig. a, the metal is displaced
axially along a mandrel, while the
internal diameter remains constant. It is usually employed to
produce cylindrical components.
Most modern flow forming machines employ two or three rollers
and their design is more
complex compared to that of spinning and shear forming machines.
The starting blank can be in
the form of a sleeve or cup. Blanks can be produced by deep
drawing or forging plus machining
to improve the dimensional accuracy. Advantages such as an
increase in hardness due to an
ability to cold work and better surface finish couples with
simple tool design and tooling cost
make flow forming a particularly attractive technique for the
production of hydraulic cylinders,
and cylindrical hollow parts with different stepped
sections.
Fig.a. Forward & Backward Flow Forming
In flow forming, as shown schematically in Fig. a, the blank is
fitted into the rotating mandrel and
the rollers approach the blank in the axial direction and
plasticise the metal under the contact point.
In this way, the wall thickness is reduced as material is
encouraged to flow mainly in the axial
direction, increasing the length of the workpiece the final
component length can be calculated as,
L1 = L0 S0(di + S0)
S1(di + S1)
Where, L1 is the workpiece length, L0 is the blank length,
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S0 is the starting wall thickness, S1 is the final wall
thickness
and di is the internal diameter.
Both spinning and flow forming can also be combined to produce
complex components. By
rotating mandrel process only cylindrical components can be
produced. Wong made observations
in his study on flow forming of solid cylindrical billets, with
different types of rollers. A flat faced
roller produces a radial flange and a non orthogonal approach of
nosed roller produces a bulge
ahead of the roller.
Materials Used in Flow forming
Stainless Steel,
Carbon Steel
Maraging Steel
Alloy Steel
Precipitated Hardened Stainless Steel
Titanium
Inconel
Hastelloy
Brass
Copper
Aluminum
Nickel
Niobium
The advantages are:
1. Low production cost.
2. Very little wastage of material.
3. Excellent surface finishes.
4. Accurate components.
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5. Improved strength properties.
6. Easy cold forming of high tensile strength alloys.
7. Production of high precision, thin walled seamless
components.
7.Shear Spinning (Shear Forming)
Before the 1950s, spinning was performed on a simple turning
lathe. When new technologies were
introduced to the field of metal spinning and powered dedicated
spinning machines were available, shear
forming started its development in Sweden.Shear forming was
first used in Sweden and grew out as
spinning.
In shear forming the area of the final component is
approximately equal to that of the blank and
little reduction in the wall thickness occurs. Whereas with
shear forming, a reduction in the wall
thickness is deliberately induced.
The starting workpiece can be thick walled circular or square
blank. Shear forming of thick
walled sheet may require two diametrically opposite roller
instead of one needed for light gauge
materials. The profile shape of the final component can be
concave, convex or combination of
these two geometries. Fig1. shows examples of products that have
been shear formed,
Fig. 1. A shear formed product: a hollow cone with a thin wall
thickness
Shear forming, also referred as shear spinning, is similar to
metal spinning. In shear spinning the
area of the final piece is approximately equal to that of the
flat sheet metal blank. The wall
thickness is maintained by controlling the gap between the
roller and the mandrel. In shear forming
a reduction of the wall thickness occurs.
The configuration of machine used in shear forming is very
similar to the conventional spinning
lathe, except that it is made more robust as higher forces are
generated during shear forming.
Nowadays on modern machines, it is common to use both shear
forming and spinning techniques
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on the same component. In shear forming, the required wall
thickness is achieved by controlling
the gap between the roller and the mandrel so that the material
is displaced axially, parallel to the
axis of rotation. Since the process involves only localised
deformation, much greater deformation
of the material can be achieved with lower forming forces as
compared with other processes. In
many cases, only a single-pass is required to produce the final
component to net shape. Moreover
due to work hardening, significant improvement in mechanical
properties can be achieved.
Operation
The shear forming process is shown in Fig. 1. blank is reduced
from the initial thickness So to a
thickness S1 by a roller moving along a cone-shaped mandrel of
half angle, During shear
forming, the material is displaced along an axis parallel to the
mandrels rotational axis as shown
in fig 2. The inclined angle of the mandrel (sometimes referred
to as half-cone angle) determines
the degree of reduction normal to the surface. The greater the
angle, the lesser will be the reduction
of wall thickness.
The final wall thickness S1 is calculated from the starting wall
thickness S0 and the inclined angle
of the mandrel
(sine law):
S1= So. sin
Fig1. Principles of shear forming
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Fig. 2. Idealised shear forming process
1. The mandrel has the interior shape of the desired final
component.
2. A roller makes the sheet metal wrap the mandrel so that it
takes its shape.
In shear forming, the starting workpiece can have circular or
rectangular cross sections. On the
other hand, the profile shape of the final component can be
concave, convex or a combination of
these two.
A shear forming machine will look very much like a conventional
spinning machine, except for
that it has to be much more robust to withstand the higher
forces necessary to perform the shearing
operation.
The design of the roller must be considered carefully, because
it affects the shape of the
component, the wall thickness, and dimensional accuracy. The
smaller the tool nose radius, the
higher the stresses and poorest thickness uniformity
achieved.
Importance of shear forming operations in manufacturing
Being able to achieve almost net shape, thin sectioned parts,
this process used widely in the
production of lightweight items. Other advantages of shear
spinning include the good mechanical
properties of the final item and a very good surface finish.
Typical components produced by mechanically powered spinning
machines include rocket nose
cones, gas turbine engine etc.
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