metal forming pdf by ([email protected])
TRANSCRIPT
UNIT 1.
ADVANCED MANUFACTURING PROCESS
Metal
Forming
Semester VII – Mechanical Engineering
SPPU
Mo.9673714743
ll EaI svaamaI samaqa- ll
aa EaI svaamaI samaqa- aa [email protected]
9673714743
Unit.1 AMP
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
Insem-Aug.2015-6M
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
METAL FORMING
Content
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1.Roll Forming
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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
(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 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. Roll forming
processes are successfully used for materials that are difficult to form by other conventional
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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.
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.In rolling the crystals get elongated in the rolling direction.
Flat rolling is illustrated in Figures 3.0 and .3.1. It involves the rolling of slabs, strips, sheets, and
plates—workparts 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.
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Rolling is the most widely used forming process, which produces products like bloom,
billet, slab, plate, strip, sheet, etc. In order to increase the flowability 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 of the workpiece movement and this friction force drags it into the roll gap. During
rolling, velocity of the workpiece increases as material flow 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.
1. Reduced labor and material handling
2. Faster, continuous production with reduced cost-per-piece
3. Greater accuracy, uniformity and consistency throughout both the individual piece and
production lots
4. The rollforming process can incorporate perforating, notching, punching, etc., thus reducing
secondary operations, parts rejections, and related costs.
5. Precision parts facilitate savings in labor and costs
6. Speedier assembly resulting from part uniformity and tighter tolerances
7. Far longer lengths are achievable
8. More surface-friendly for prepainted, precoated and preplated metals
9.Two separate pieces/materials can be simultaneously formed, in a
single operation, to produce a strong composite part
9 (Insem-Aug.2015. 6M)
Hydroforming was developed in the late 1940's and early 1950's to provide a cost effective
means to produce relatively small quantities of drawn parts or parts with asymmetrical or irregular
contours that do not lend themselves to stamping. Virtually all metals capable of cold forming can
be hydroformed, including aluminum, brass, carbon and stainless steel, copper, and high strength
alloys.
In hydroforming, high viscous fluid 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.
A hydroforming press operates like the upper or female die element. This consists of a
pressurized forming chamber of oil, a rubber diaphragm and a wear pad. The lower or male die
Advantages
.
2. High Velocity Hydro Forming
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element, is replaced by a punch and ring. The punch is attached to a hydraulic piston, and the blank
holder, or ring, which surrounds the punch. The hydroforming process begins by placing a metal
blank on the ring. The press is closed bringing the chamber of oil down on top of the blank. The
forming chamber is pressurized with oil while the punch is raised through the ring and into the the
forming chamber. Since the female portion of this forming method is rubber, the blank is formed
without the scratches associated with stamping. The diaphragm supports the entire surface of the
blank. It forms the blank around the rising punch, and the blank takes on the shape of the punch.
When the hydroforming cycle is complete, the pressure in the forming chamber is released and the
punch is retracted from the finished part.
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
Applications
Automotive industry, sport car industry , shaping of aluminium tubes for bicycle
frames.
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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
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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APPLICATIONS
Automotive industry,
Aerospace-Lighter, stiffer parts,kitchen spoutes.
ADVANTAGES
Weight reduction .
Inexpensive tooling costs and reduced set-up time.
Reduced development costs.
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.
Shock lines, draw marks, wrinkling, and tearing associated with matched die forming are
eliminated.
Material thinout is minimized.
Low Work-Hardening
Multiple conventional draw operations can be replaced by one cycle in a hydroforming
press.
Ideal for complex shapes and irregular contours.
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.
( Insem –Aug.2015-6M )
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 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
3. Electromagnetic Forming
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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.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 are less
costly, and are also preferred when a high energy level is needed. 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.
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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, with a typical electromagnetic
forming system for shaping hollow cylindrical objects.
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. 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 .
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.
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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.
10. It is an environmentally clean process as no lubricants are necessary.
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.
Working
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
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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.
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.
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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.
Applications:
i) Crimping of coils, tubes, wires
ii) Bending of tubes into complex shapes.
iii) Bulging of thin tubes.
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. 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. 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.
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
4. High Energy Rate Forming (HERF)
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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 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.
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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.
• 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
1. Production rates are higher, as parts are made at a rapid rate.
2. Die costs are relatively lower.
3. Tolerances can be easily maintained.
4. Versatility of the process – it is possible to form most metals including difficult to form
metals.
5. No or minimum spring back effect on the material after the process.
6. Production cost is low as power hammer (or press) is eliminated in the process. Hence it is
economically justifiable.
7. Complex shapes / profiles can be made much easily, as compared to conventional forming.
8) The required final shape/ dimensions are obtained in one stroke (or step), thus eliminating
intermediate forming steps and pre forming dies.
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9) 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
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
Insem-Aug.2015-4M
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 .
Operation.
5. Spinning
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Fig.Spinning Setup
In manual spinning, a circular blank of a flat 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. 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. 1 and Fig 2; these shapes are difficult 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.
Fig. 1 Schematic diagram of the manual metal- spinning process, showing the deformation of a
metal disk over a mandrel to form a cone
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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. 2. 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 reflectors
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 “sheep’s nose” and “duck’s bill.” The first manual spinning machine was
developed in the 1930s. Manual metal spinning involves no significant 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
flow stress and thereby allow thicker sections to be formed. Manual metal spinning is used to form
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cups, cones, flanges, 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 reflectors, tank ends, covers, housings, shields, and
components for musical instruments.
Fig. 3 Photograph of conical components that were produced by metal spinning.
ADVANTAGES
1. Sevaral operation can be performed in one set up.
2. Production cost low.
3. 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).
4. The setup time is shorter than for forging.
5. The design changes in the workpiece can be made at relatively low cost.
DISADVANTAGES
1. Highly skilled operators are required, because the uniformity of the formed part depends to
a large degree on the skill of the operator.
2. Manual metal spinning is usually significantly slower than press forming.
3. The deformation loads available are much lower in manual metal spinning than in press
forming.
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Flow forming is a modernized, improved advanced version of metal spinning, which is
one of the oldest methods of chipless forming. The metal spinning method used a pivoted pointer
to manually push a metal sheet mounted at one end of a spinning mandrel. This method was used
to fabricate axisymmetric, thin‐walled, light‐weight 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.
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.1. 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
6. Flow Forming
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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.
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
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parts with different stepped sections.
Fig.1. 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,
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.
Forward Spinning
Backward Spinning
Headstock
Mandrel
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Features The unique features of the flow forming process allow for innovative, cost-
effective engineering or redesign of your product or part, resulting in the following
features:
1. Traditional multi-piece designs can be formed as a single, seamless piece.
2. Increase mechanical properties, such as tensile/yield strength and hardness.
3. Provide design versatility to produce a unique seamless profile with varying wall
thicknesses.
4. Produce cylindrical, conical, or contoured shapes up to 47" diameter.
5. Typical interior finishes of 15Ra without additional manufacturing steps.
6. High material utilization from near-net shape forming process.
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.
5. Improved strength properties.
6. Easy cold forming of high tensile strength alloys.
7. Production of high precision, thin walled seamless components.
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Insem- Aug. 4M
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 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
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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, α During shear
forming, the material is displaced along an axis parallel to the mandrel’s 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
α (sine law):
S1= So. sinα
Fig1. Principles of shear forming
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.
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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.
Advantages.
1. Good mechanical properties 2. This process used widely in the production of lightweight items. 3. Very good surface finish.
4. dimensional accuracy.
Applications
Typical components produced by mechanically powered spinning machines include rocket nose
cones, gas turbine engine etc. Being able to achieve almost net shape, thin sectioned parts.
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