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ll EaI svaamaI samaqa- ll
aa EaI svaamaI samaqa- aa [email protected]
9673714743
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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 α exceeds the friction angle λ 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
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.
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
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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 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. In
order to make the analysis of flat rolling process simple, assumptions like plane strain deformation,
volume constancy principle, constant coefficient of friction, constant surface velocity of the rolls,
etc., are considered. Out of all varieties of the rolling processes, the flat rolling is the most practical
one which produces around 40–60 % of the total rolled products.
2. High Velocity Hydro Forming
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. 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 flat 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 first 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 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. 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 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.
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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 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
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flow stress and thereby allow thicker sections to be formed. Manual metal spinning is used to form
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. 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 significantly 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, 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.
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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, 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
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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.
***THANK YOU***
II Shri Swami Samarth II
Unit. 2 AMP
Advanced Welding, Casting and Forging processes
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Content
Friction Stir Welding – Introduction, Tooling, Temperature distribution and resulting melt flow
Advanced Die Casting - Vacuum Die casting, Squeeze Casting
Welding :-
Welding is the process of joining together pieces of metal or metallic parts by bringing
them into intimate proximity and heating the place of content to a state of fusion or plasticity.
1. Key features of welding:-
The welding structures are normally lighter than riveted or bolted structures.
The welding joints provide maximum efficiency, which is not possible in other type of
joints.
The addition and alterations can be easily made in the existing structure.
A welded joint has a great strength.
The welding provides very rigid joints.
The process of welding takes less time than other type of joints.
2. Largely used in the following fields of engineering:-
Manufacturing of machine tools, auto parts, cycle parts, etc.
Fabrication of farm machinery & equipment.
Fabrication of buildings, bridges & ships.
Construction of boilers, furnaces, railways, cars, aeroplanes, rockets and missiles.
Manufacturing of television sets, refrigerators, kitchen cabinets, etc.
1. Friction Stir Welding :-
Friction Stir Welding (FSW) was invented by Wayne Thomas at TWI (The Welding Institute),
and the first patent applications were filed in the UK in December 1991. Initially, the process was
regarded as a “laboratory” curiosity, but it soon became clear that FSW offers numerous benefits
in the fabrication of aluminium products. Friction Stir Welding is a solid-state process, which
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means that the objects are joined without reaching melting point. This opens up whole new areas
in welding technology. Using FSW, rapid and high quality welds of 2xxx and 7xxx series alloys,
traditionally considered unweldable, are now possible.
Friction stir welding (FSW), illustrated in Figure. 1, is a solid state welding process in
which a rotating tool is fed along the joint line between two workpieces, generating friction heat
and mechanically stirring the metal to form the weld seam. The process derives its name from this
stirring or mixing action. FSW is distinguished from conventional FRW by the fact that friction
heat is generated by a separate wear-resistant tool rather than by the parts themselves.
The rotating tool is stepped, consisting of a cylindrical shoulder and a smaller probe
projecting beneath it. During welding, the shoulder rubs against the top surfaces of the two parts,
developing much of the friction heat, while the probe generates additional heat by mechanically
mixing the metal along the butt surfaces. The probe has a geometry designed to facilitate the
mixing action. The heat produced by the combination of friction and mixing does not melt the
metal but softens it to a highly plastic condition.
Figure 1. Friction stir welding (FSW): (1) rotating tool just prior to feeding into
joint and (2) partially completed weld seam. N=tool rotation, f=tool feed.
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As the tool is fed forward along the joint, the leading surface of the rotating probe forces the metal
around it and into its wake, developing forces that forge the metal into a weld seam. The shoulder
serves to constrain the plasticized metal flowing around the probe.
Friction Stir Welding can be used to join aluminium sheets and plates without filler wire
or shielding gas. Material thicknesses ranging from 0.5 to 65 mm can be welded from one side at
full penetration, without porosity or internal voids. In terms of materials, the focus has traditionally
been on non-ferrous alloys, but recent advances have challenged this assumption, enabling FSW
to be applied to a broad range of materials.
To assure high repeatability and quality when using FSW, the equipment must possess
certain features. Most simple welds can be performed with a conventional CNC machine, but as
material thickness increases and “arc-time” is extended, purpose-built FSW equipment becomes
essential.
1.0 Process characteristics
The FSW process involves joint formation below the base material’s melting temperature.
The heat generated in the joint area is typically about 80-90% of the melting temperature.
With arc welding, calculating heat input is critically important when preparing welding
procedure specifications (WPS) for the production process. With FSW, the traditional
components current and voltage are not present as the heat input is purely mechanical and thereby
replaced by force, friction, and rotation. Several studies have been conducted to identify the way
heat is generated and transferred to the joint area. A simplified model is described in the following
equation:
Q = µωFK
in which the heat (Q) is the result of friction (μ), tool rotation speed (ω) down force (F) and a tool
geometry constant (K).
The quality of an FSW joint is always superior to conventional fusion-welded joints. A
number of properties support this claim, including FSW’s superior fatigue characteristics.
1.1 Welding parameters
In providing proper contact and thereby ensuring a high quality weld, the most important
control feature is down force (Z-axis). This guarantees high quality even where tolerance errors in
the materials to be joined may arise. It also enables robust control during higher welding speeds,
as the down force will ensure the generation of frictional heat to soften the material.
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When using FSW, the following parameters must be controlled: down force, welding
speed, the rotation speed of the welding tool and tilting angle. Only four main parameters need to
be mastered, making FSW ideal for mechanised welding.
1.2 Tools for welding
Welding tool design is critical in FSW. Optimising tool geometry to produce more heat
or achieve more efficient “stirring” offers two main benefits: improved breaking and mixing of
the oxide layer and more efficient heat generation, yielding higher welding speeds and, of course,
enhanced quality.
The simplest tool can be machined from an M20 bolt with very little effort. It has proved
feasible to weld thin aluminium plates, even with tooling as simple as this, although at very slow
welding speeds. However, tool materials should feature relatively high hardness at elevated
temperatures, and should retain this hardness for an extended period. The combination of tool
material and base material is therefore always crucial to the tool’s operational lifetime.
1.3 Tools for steels
To apply FSW in steel or other high-temperature materials, the difficulty is mainly
associated with finding proper tool material; a material that can withstand the high temperatures
that are experienced during the process. Resistance to wear (durability) is one important aspect,
especially as many of the intended applications are considered critical; hence there can be no traces
of the tool left in the seam. One of the most promising tool materials so far is the so called PCBN
(polycrystalline cubic boron nitride), which is manufactured by MegaStir.
1.4 Retractable pin tool
The Retractable Pin Tool (RPT) or Adjustable Probe Tool is a machine feature in which the pin
of the FSW tool may be moved independently of the tool’s shoulder. This permits adjustments of
the pin length to be made during welding, to compensate for known material thickness variations
or to close the exit hole of the weld.
Advantages
(1) Good mechanical properties of the weld joint,
(2) Avoidance of toxic fumes, warping, shielding issues, and other problems associated with arc
welding,
(3) Little distortion or shrinkage,
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(4) Good weld appearance.
(5) Less post-treatment and impact on the environment
(6) Energy saving FSW process
(7) Less weld-seam preparation
(8) Improved joint efficiency, Improved energy efficiency
(9) Less distortion – low heat input
(10) Increased fatigue life
Disadvantages
(1) an exit hole is produced when the tool is withdrawn from the work, and
(2) heavy-duty clamping of the parts is required.
Application
It is used in aerospace, automotive, Civil aviation , railway, and shipbuilding industries.
Automotive applications
In principle, all aluminium components in a car can be friction stir welded: bumper beams, rear
spoilers, crash boxes, alloy wheels, air suspension systems, rear axles, drive shafts, intake
manifolds, stiffening frames, water coolers, engine blocks, cylinder heads, dashboards, roll-over
beams, pistons, etc.
In larger road transport vehicles, the scope for applications is even wider and easier to adapt
– long, straight or curved welds: trailer beams, cabins and doors, spoilers, front walls, closed body
or curtains, dropside walls, frames, rear doors and tail lifts, floors, sides, front and rear bumpers,
chassis ,fuel and air containers, toolboxes, wheels, engine parts, etc.
Typical applications are butt joints on large aluminum parts. Other metals, including steel,
copper, and titanium, as well as polymers and composites have also been joined using FSW.
2. Introduction to Tooling The word tooling refers to the hardware necessary to produce a particular product. The
most common classification of tooling is as follows:
1. Sheet metal press working tools.
2. Molds and tools for plastic molding and die casting.
3. Jigs and fixtures for guiding the tool and holding the work piece.
4. Forging tools for hot and cold forging.
5. Gauges and measuring instruments.
6. Cutting tools such as drills, reamers, milling cutters broaches, taps, etc.
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2.1. Sheet metal press working tools.
Sheet metal press working tools are custom built to produce a component mainly out of
sheet metal. Press tool is of stampings including cutting operations like shearing, blanking,
piercing etc. and forming operations like bending, drawing etc. Sheet metal items such as
automobile parts (roofs, fenders, caps, etc.) components of aircrafts parts of business machines,
household appliances, sheet metal parts of electronic equipments, Precision parts required for
horlogical industry etc, are manufactured by press tools.
2.2. Molds and tools for plastic molding and die casting.
The primary function of a mould or the die casting die is to shape the finished product. In
other words, it is imparting the desired shape to the plasticized polymer or molten metal and
cooling it to get the part. It is basically made up of two sets of components. i) The cavity & core
ii) The base in which the cavity & core are mounted. Different mould construction methods are
used in the industry. The mould is loaded on to a machine where the plastic material or molten
material can be plasticized or melted, injected and ejected.
2.3. Jigs and fixtures for guiding the tool and holding the work piece.
To produce products and components in large quantities with a high degree of accuracy
and Interchangeability, at a competitive cost, specially designed tooling is to be used. Jigs and
fixtures are manufacturing equipments, which make hand or machine work easier. By using such
tooling, we can reduce the fatigue of the operator (operations such as marking) and shall give
accuracy and increases the production. Further the use of specially designed tooling will lead to
an improvement of accuracy, quality of the product and to the satisfaction of the consumer and
community. A jig is a device in which a work piece/component is held and located for a specific
operation in such a way, that it will guide one or more cutting tools. A fixture is a work holding
device used to locate accurately and to hold securely one or more work pieces so that the required
machining operations can be performed.
2.4 Press tools Press working is used as general term to cover all press working operations on sheet metal.
The stamping of parts from sheet metal is shaped or cur through deformation by shearing,
punching, drawing, stretching, bending, coining etc. Production rates are high and secondary
machining is not required to produce finished parts with in tolerance. A pressed part may be
produce by one or a combination of three fundamental press operations. They include:
1. Cutting (blanking, piercing, lancing etc) to a predetermined configuration by exceeding
the shear strength of the material.
2. Forming (drawing or bending) whereby the desired part shape is achieved by
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overcoming the tensile resistance of the material.
3. Coining (compression, squeezing, or forging) which accomplishes surface
displacement by overcoming the compressive strength of the material.
Whether applied to blanking or forming the under laying principle of stamping process
may be desired as the use of force and pressure to cut a piece of sheet metal in to the desired shape.
Part shape is produced by the punch and die, which are positioned in the stamping press. In most
production operations the sheet metal is placed on the die and the descending punch is forced into
the work piece by the press. Inherent characteristics of the stamping process make it versatile and
foster wide usage. Costs tend to be low, since complex parts can be made in few operations at high
production rates.
Blanking
When a component is produced with one single punch and die with entire perifery is cut is
called Blanking. Stampings having an irregular contour must be blanked from the strip. Piercing,
embossing, and various other operations may be performed on the strip prior to the blanking
station.
Piercing
Piercing involves cutting of clean holes with resulting scrape slug. The operation is often called
piercing, although piercing is properly used to identify the operation for the producing by tearing
action, which is not typical of cutting operation. In general the term piercing is used to describe
die cut holes regardless of size and shape. Piecing is performed in a press with the die.
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Cut-off
Cut off operations are those in which strip of suitable width is cut to lengthen single.
Preliminary operations before cutting off include piercing, notching, and embossing. Although
they are relatively simple, cut-off tools can produce many parts.
Parting off
Parting off is an operation involve two cut off operations to produce blank from the strip.
During parting some scrape is produced. Therefore parting is the next best method for cutting
blanks. It is used when blanks will not rest perfectly. It is similar to cut off operation except the
cut is in double line. This is done for components with two straight surfaces and two profile
surfaces.
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Perforating:
Perforating is also called as piercing operation. It is used to pierce many holes in a
component at one shot with specific pattern.
Trimming
When cups and shells are drawn from flat sheet metal the edge is left wavy and irregular,
due to uneven flow of metal. This irregular edge is trimmed in a trimming die. Shown is flanged
shell, as well as the trimmed ring removed from around the edge. While a small amount of Material
is removed from the side of a component or strip is also called as trimming.
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Shaving
Shaving removes a small amount of material around the edges of a previously blanked
stampings or piercing. A straight, smooth edge is provided and therefore shaving is frequently
performed on instrument parts, watch and clock parts and the like. Shaving is accomplished in
shaving tools especially designed for the purpose.
Broaching
Figure shows serrations applied in the edges of a stamping. These would be broached in a
broaching tool. Broaching operations are similar to shaving operations. A series of teeth removes
metal instead of just one tooth’s in shaving. Broaching must be used when more material is to be
removed than could effectively done in with one tooth.
Side piercing (cam operations)
Piercing a number of holes simultaneously around a shells done in a side cam tool; side
cams convert the up and down motion of the press ram into horizontal or angular motion when it
is required in the nature of the work.
Dinking
To cut paper, leather, cloth, rubber and other soft materials a dinking tool is used. The cutting
edges penetrate the material and cuts. The die will be usually a plane material like wood or hard
rubber.
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Lancing
Lancing is cutting along a line in a product without feeling the scrape from the product.
Lancing cuts are necessary to create lovers, which are formed in sheet metal for venting function.
Bending Bending tools apply simple bends to stampings. A simple bend is done in which the line of
bend is straight. One or more bends may be involved, and bending tools are a large important class
of pres tools.
Forming
Forming tools apply more complex forms to work pieces. The line of bend is curved
instead of straight and the metal is subjected to plastic flow or deformation.
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Drawing
Drawing tools transform flat sheets of metal into cups, shells or other drawn shapes by
subjecting the material to severe plastic deformation. Shown in fig is a rather deep shell that has
been drawn from a flat sheet.
Curling
Curling tools curl the edges of a drawn shell to provide strength and rigidity. The curl
may be applied over aware ring for increased strength. You may have seen the tops of the sheet
metal piece curled in this manner. Flat parts may be curled also. A good example would be a
hinge in which both members are curled to provide a hole for the hinge pin.
Bulging
Bulging tools expand the bottom of the previously drawn shells. The bulged bottoms of
some types of coffee pots are formed in bulging tools.
Swaging
In swaging operations, drawn shells or tubes are reduced in diameter for a portion of their
lengths.
Extruding
Extruding tools cause metal to be extruded or squeezed out, much as toothpaste is extruded
from its tube when pressure is applied. Figure shows a collapsible tool formed and extruded from
a solid slug of metal.
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Cold forming
In cold forming operations, metal is subjected to high-pressure and caused to and flow into
a pre determined form. In coining, the metal is caused to flow into the shape of the die cavity Coins
such as nickels, dimes and quarters are produced in coining tools.
Flaring, lugging or collar drawing
Flanging or collar drawing is a operation in which a collar is formed so that more number
of threads can be provided. The collar wall can also be used as rivet when two sheets are to be
fastened together.
Planishing
Planishing tool is used to straighten, blanked components. Very fine serration points
penetrate all around the surface of the component
Assembly tools
Represented is an assembly tool operation where two studs are riveted at the end of a link.
Assembly tools assemble the parts with great speed and they are being used more and more.
Combination tool
In combination tool two or more operations such as forming, drawing, extruding,
embossing may be combined on the component with various cutting operations like blanking,
piercing, broaching and cut off
Processes
Other production machines include presses for stamping operations, forge hammers for
forging, rolling mills for rolling sheet metal, welding machines for welding, and insertion
machines for inserting electronic components into printed circuit boards. The name of the
equipment usually follows from the name of the process.
The type of tooling depends on the type of manufacturing process. Table.1, lists examples
of special tooling used in various operations
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Table 1. Production equipment and tooling used for various manufacturing processes.
Process Tooling
(Function)
Equipment Special Tooling (Function)
Casting Various types of casting
setups and equipment
Mold (cavity for molten metal)
Molding Molding machine Mold (cavity for hot polymer)
Rolling Rolling mill Roll (reduce work thickness)
Forging Forge hammer or press Die (squeeze work to shape)
Extrusion Press Extrusion die (reduce cross-section)
Stamping Press Die (shearing, forming sheet metal)
Machining Machine tool Cutting tool (material removal)
Fixture (hold workpart)
Jig (hold part and guide tool)
Grinding Grinding machine Grinding wheel (material removal)
Welding Welding machine Electrode (fusion of work metal)
Fixture (hold parts during welding)
Production machinery usually requires tooling that customizes the equipment for the particular
part or product. In many cases, the tooling must be designed specifically for the part or product
configuration. When used with general purpose equipment, it is designed to be exchanged. For
each work part type, the tooling is fastened to the machine and the production run is made. When
the run is completed, the tooling is changed for the next workpart type. When used with special
purpose machines, the tooling is often designed as an integral part of the machine. Because the
special purpose machine is likely being used for mass production, the tooling may never need
changing except for replacement of worn components or for repair of worn surfaces.
3. Die Casting
Die casting is a permanent-mold casting process in which the molten metal is injected into
the mold cavity under high pressure. Typical pressures are 7 to 350 MPa (1015–50,763 lb/in2).
The pressure is maintained during solidification, after which the mold is opened and the part is
removed. Molds in this casting operation are called dies; hence the name die casting.
Two basic conventional die casting processes exist: the hot- chamber process and the
cold-chamber process. These descriptions stem from the design of the metal injection systems
utilized.
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A schematic of a hot-chamber die casting machine is shown in Figure 1.2. A significant
portion of the metal injection system is immersed in the molten metal at all times. This helps keep
cycle times to a minimum, as molten metal needs to travel only a very short distance for each
cycle. Hot-chamber machines are rapid in operation with cycle times varying from less than 1 sec
for small components weighing less than a few grams to 30 sec for castings of several kilograms.
Dies are normally filled between 5 and 40 msec. Hot-chamber die casting is traditionally used for
low melting point metals, such as lead or zinc alloys. Higher melting point metals, including
aluminum alloys, cause rapid degradation of the metal injection system.
Cold-chamber die casting machines are typically used to con- ventionally die cast
components using brass and aluminum alloys. An illustration of a cold-chamber die casting
machine is presented in Figure 1.3. Unlike the hot-chamber machine, the metal injection system is
only in contact with the molten metal for a short period of time. Liquid metal is ladled (or metered
by some other method) into the shot sleeve for each cycle.
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To provide further protection, the die cavity and plunger tip normally are sprayed with an oil or
lubricant. This increases die material life and reduces the adhesion of the solidified component.
Conventional die casting is an efficient and economical process. When used to its
maximum potential, a die cast component may replace an assembly composed of a variety of parts
produced by various manufacturing processes. Consolidation into a single die casting can
significantly reduce cost and labor.
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3.1 METAL FLOW IN VACUUM DIE CASTING
In conventional die casting, high gate velocities result in atomized metal flow within the
die cavity, as shown in Figures 2.8 and 2.9. Entrapped gas is unavoidable. This phenomenon is
also present in vacuum die casting, as the process parameters are virtually iden- tical to that of
conventional die casting.
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3.2 METAL FLOW IN SQUEEZE CASTING
Due to larger gate cross sections and longer fill times in comparison to conventional die casting,
atomization of the liquid metal is avoided when squeeze casting. Both planar and nonplanar flows
occur in squeeze casting. Achieving planar flow, however, is dependent on the die design and
optimization of the process para- meters. Figure 2.10 is a picture showing two short shots of
identical castings. In Figure 2.10a planar filling occurred within the die, while nonplanar filling
occurred in Figure 2.10 b.
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These differences in metal flow were made possible by adjusting machine-controlled process
parameters. Be that as it may, for complex component geometries, nonplanar fill may be
unavoidable.
4. VACUUM DIE CASTING
Entrapped gas is a major source of porosity in conventional die castings. Vacuum die
casting is characterized by the use of a con- trolled vacuum to extract gases from the die cavities,
runner sys- tem, and shot sleeve during processing.
Numerous metal casting processes have utilized vacuum systems to assist in the removal of
unwanted gases. These processes include permanent-mold casting, lost-foam casting, plaster mold
casting, and investment casting. The constraint in the evolution of vacuum die casting has been
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the development of a reliable vacuum shut-off valve. Vacuum die casting is compatible with other
high integrity processes, including squeeze casting.
Fig.4.1 Layout of early developed vacuum process
The vacuum die casting process minimizes gas entrapment by removing gases from the cavity
generated by two of these mechanisms. Both air in the die cavity and gases generated by the
decomposition of lubricants can be removed using the vacuum die casting process. In conventional
die casting, gases are typically vented from the die. However, the amount of gas that must vent
from the dies is much greater than that of just the die cavity. All gases in the runner system must
be vented as well as any volume of the shot sleeve not filled with metal. When examining the
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volume of gas that must be evacuated from the die combined with the short cycle times of
conventional die casting, one finds that it is virtually impossible for all gases to exit the die before
die fill is complete.
Fig.4.2 Schematic drawing of vacuum die casting process
The vacuum die casting process utilizes a conventional die casting machine coupled with a
vacuum system. This system is composed of a vacuum pump, a vacuum shut-off valve, a vacuum
control system, and an unvented die.
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Vacuum die casting builds upon conventional die casting practices by minimizing the
effects of a major contributor to porosity. The cycle time and economics of vacuum die casting are
equivalent to conventional die casting. The only economic penalty in using vacuum die casting is
the capital cost of the vacuum system and its operation. These additional costs, however, are minor
in comparison to increased component integrity. In converting conventional die castings to vacuum
die castings, one must consider the benefits that are sought. If porosity from gas entrapment is a
problem, vacuum die casting can offer improvements. If shrinkage porosity is an issue, other high
integrity die casting processes should be utilized.
4.1 Characteristics of vacuum die casting process
Vacuum process has been recognized as an efficient die-casting process to eliminate defects, such
as blowhole, cold shut, flow line and misrun. At casting site, reduction of shot speed and metal
pressure prevents burrs remarkably, and it also prolongs die life, eliminates deburring operation
and increases up time of casting machine. In starting up new parts, good parts can be easily
obtained. Modification process of die tooling can be reduced, and totally new product can be
introduced into mass production in a relatively short period of time. But there are some
disadvantages. One of them is that aluminum melt can intrude into vacuum line when aluminum
dreg stuck at shutting valve sheet during last shot.
5. Squeeze casting
Porosity often limits the use of the conventional die casting pro- cess in favor of products
fabricated by other means. Several efforts have successfully stretched the capabilities of
conventional die casting while preserving its economic benefits. In these efforts, squeeze casting
utilizes two strategies :
1. eliminating or reducing the amount of entrapped gases and
2. eliminating or reducing the amount of solidification shrinkage.
Squeeze casting is a Combination of casting and forging in which a molten metal is poured into a
preheated lower die, and the upper die is closed to create the mold cavity after solidification begins.
This differs from the usual permanent-mold casting process in which the die halves are closed
prior to pouring or injection. Owing to the hybrid nature of the process, it is also known as liquid
metal forging.
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Squeeze casting is characterized by the use of a large gate area (in comparison to
conventional die casting) and planar filling of the metal front within the die cavity. Squeeze casting
works to minimize both solidification shrinkage and gas entrapment. Planar filling allows gases to
escape from the die, as vents remain open throughout metal injection. Moreover, the large gate
area allows metal intensification pressure to be maintained throughout solidification.
The origins of the squeeze casting process can be traced back to a process known as squeeze
forming. A schematic showing the progressive cycle of the squeeze forming process is shown in
Figure 5. Initially, liquid metal is poured into an open die, as shown in Figure 5,a. The die is
closed (Figure 5,b) and the metal flows within the die, filling the cavity.
Figure 5. Schematic of the squeeze forming process.
During solidification, an intensification pressure is applied to the metal by the dies. After
solidification is complete, the component is ejected, as presented in Figure 5, c.
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Squeeze casting process parameters are very similar to conventional die casting in that the liquid
metal is pressurized during solidification. The major difference between squeeze casting and
conventional die casting is with regards to the gate velocity. Gate velocities are often achieved
during squeeze casting that are orders of magnitude slower than in conventional die casting. The
gate velocities in squeeze casting can be as low as those characteristic to permanent-mold casting.
Cycles times for squeeze casting are longer than those of conventional die casting. This is due to
both the slower metal injection speeds and the longer solidification times. The resulting
microstructures are much different. The microstructure in the squeeze casting is not as fine as that
observed in conventional die casting, and the dendrites are much more pronounced. The
mechanical properties of squeeze castings are much improved due to reduced levels of porosity
and the formation of micro- structures not possible in conventionally die cast components.
5.1 ELEMENTS OF SQUEEZE CASTING MANUFACTURING EQUIPMENT
Both horizontal and vertical conventional die casting machines can be used in conjunction
with the squeeze casting process. The differences in squeeze casting are attributed to the die design
and process parameters.
In comparison to conventional die casting, squeeze casting dies have larger gate areas.
Gates are no less than 3 mm in thickness to avoid premature solidification during intensification.
Some manufacturers utilize classical fan gating such as that used in conventional die casting. Other
producers have found large single- point gates ideal.
As squeeze castings have thicker gates, trimming is not a viable option to removing
components from their runner systems. Sawing is typically required. Automated sawing systems
are available for high volume production. However, automated systems require customer fixtures.
Although sawing may be necessary for removing components from their respective runner
systems, trimming often is not avoided. The removal of overflows and flash is still accomplished
using traditional trimming techniques.
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As with any die casting process, shot control is essential. Often the shot control systems
currently available on conventional die casting machines may be used with the squeeze casting
process. Process parameters, however, must be adjusted to allow for slower fill of the die cavity
and longer intensification times. Key process characteristics of squeeze casting include metal
temperature, melt cleanliness, cavity pressure, and gate velocities.
5.2 Difference Between CDE & Squeeze
Squeeze casting is a high integrity die casting process that builds upon conventional die
casting practices and is compatible with aluminum, magnesium, zinc, and copper alloy systems.
Cycle times are longer in comparison to conventional die casting due to longer metal injection
durations. Component integrity is improved by minimizing entrapped air and reducing
solidification shrinkage. Most squeeze casting components can be heat treated without blis-tering
defects to improve mechanical properties.
Conventional die casting is lower cost in the areas of capital equipment. Squeeze casting
has addi- tional costs associated with automated sawing for separating the runner system from
squeeze cast components. A saw must be purchased, operated, and maintained along with fixturing.
These additional costs, however, are often offset with benefits in the areas of porosity
reduction related to solidification shrink- age, which improves mechanical properties. Moreover,
the reduc- tion in entrapped gas results in a heat-treatable casting.
In converting conventional die castings to squeeze castings, one must consider the benefits
sought. If porosity from gas entrapment and solidification is a problem, squeeze casting can offer
improve- ments. If only entrapped gas is an issue, vacuum die casting may be sufficient. Moreover,
squeeze casting can be combined with vacuum die casting. The use of a vacuum system during
squeeze casting can further reduce entrapped gas beyond that normally achieved when squeeze
casting.
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A qualitative comparison of these two processes is shown in Figure 5.2.
+ = indicates favorable rating
Figure 5.2. Comparisons of conventional die casting and squeeze casting
Advantages
No Blow Hole
Heat treatable
Weld-able
No Shrinkage porosity
Infiltration of preformed insert (MMC)
Application
Fuel pipe, Scroll, Rack housing, Wheel, Suspension arm, Brake caliper, No Shrinkage porosity,
Cross member node, Engine block, Brake disc, Piston.
********** Thank You ***********
II Shri Swami Samarth II
Unit.3 AMP
Advanced Techniques For Material Processing
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Content
1. STEM: Shape tube Electrolytic machining,
2. EJT: Electro Jet Machining,
3. ELID: Electrolytic In-process Dressing,
4. ECG: Electrochemical Grinding,
5. ECH: Elctro-chemical Etching
6. LBHT : Laser based Heat Treatment
1.Shape Tube Electrolytic Machining (STEM) :-
Shaped tube electrolytic machining (STEM) is based on the dissolution process when
an electric potential difference is imposed between the anodic workpiece and a cathodic tool.
Because of the presence of this electric field the electrolyte, often a sulfuric acid, causes the anode
surface to be removed. After the metal ions are dissolved in the solution, they are removed by the
electrolyte flow. As shown in Fig. 1 and according to McGeough (1988), the tool is a conducting
cylinder with an insulating coating on the outside and is moved toward the workpiece at a certain
feed rate while a voltage is applied across the machining gap. In this way a cylindrically shaped
hole is obtained.
Fig.1 STEM Schematic
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STEM is, therefore, a modified variation of the ECM that uses acid electrolytes. Rumyantsev and
Davydov (1984) reported that the process is capable of producing small holes with diameters of
0.76 to 1.62 mm and a depth-to-diameter ratio of 180:1 in electrically con- ductive materials. It is
difficult to machine such small holes using normal ECM as the insoluble precipitates produced
obstruct the flow path of the electrolyte.
The machining system configuration is similar to that used in ECM. However, it must be
acid resistant, be of less rigidity, and have a periodically reverse polarity power supply. The
cathodic tool electrode is made of titanium, its outer wall having an insulating coating to permit
only frontal machining of the anodic workpiece. The normal operating voltage is 8 to 14 V dc,
while the machining current reaches 600 A. The Metals Handbook (1989) reports that when a nitric
acid electrolyte solution (15% v/v, temperature of about 20°C) is pumped through the gap (at 1
L/min, 10 V, tool feed rate of 2.2 mm/min) to machine a 0.58-mm- diameter hole with 133 mm
depth, the resulting diametral overcut is 0.265 mm, and the hole conicity is 0.01/133.
The process also uses a 10% concentration sulfuric acid to prevent the sludge from
clogging the tiny cathode and ensure an even flow of electrolyte through the tube. A periodic
reversal of polarity, typically at 3 to 9 s pre- vents the accumulation of the undissolved machining
products on the cathode drill surface. The reverse voltage can be taken as 0.1 to 1 times the forward
machining voltage. In contrast to the EDM, EBM, and LBM processes, STEM does not leave a
heat-affected layer, which is liable to develop microcracks.
Process parameters
Electrolyte
Type Sulfuric, nitric, and hydrochloric acids
Concentration 10–25% weight in water
Temperature 38°C (sulfuric acid) 21°C (others)
Pressure 275–500 kPa
Voltage
Forward 8–14 V
Reverse 0.1–1 times the forward
Time
Forward 5–7 s
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Reverse 25–77 ms
Feed rate 0.75–3 mm/min
Process capabilities
Hole size 0.5–6 mm diameter at an aspect ratio of 150
Hole tolerances 0.5-mm diameter ±0.050 mm
1.5-mm diameter ±0.075 mm
60-mm diameter ±0.100 mm
Hole depth ±0.050 mm
Because the process uses acid electrolytes, its use is limited to drilling holes in stainless
steel or other corrosion-resistant materials in jet engines and gas turbine parts such as,
■ Turbine blade cooling holes
■ Fuel nozzles
■ Any holes where EDM recast is not desirable
■ Starting holes for wire EDM
■ Drilling holes for corrosion-resistant metals of low conventional machinability
■ Drilling oil passages in bearings where EDM causes cracks.
Fig.2, Turbulated cooling holes produced by STEM
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Figure 2. shows the shape of turbulators that are machined by intermittent drill advance during
STEM. The turbulators are normally used for enhancing the heat transfer in turbine engine-cooling
holes.
* Advantages
■ The depth-to-diameter ratio can be as high as 300.
■ A large number of holes (up to 200) can be drilled in the same run.
■ Nonparallel holes can be machined.
■ Blind holes can be drilled.
■ No recast layer or metallurgical defects are produced.
■ Shaped and curved holes as well as slots can be produced.
* Limitations
■ The process is used for corrosion-resistant metals.
■ STEM is slow if single holes are to be drilled.
■ A special workplace and environment are required when handling acid.
■ Hazardous waste is generated.
■ Complex machining and tooling systems are required.
2. Electrolytic In-process Dressing
Electrolytic in-process dressing (ELID) is traditionally used as a method of dressing a
metal bonded grind- ing wheel during a precision grinding process. The Electrolytic In-process
Dressing (ELID) is a new technique that is used for dressing harder metal-bonded superabrasive
grinding wheels while performing grinding. Though the application of ELID eliminates the wheel
loading problems, it makes grinding as a hybrid process. The ELID grinding process is the
combination of an electrolytic process and a mechanical process and hence if there is a change in
any one of the processes this may have a strong influence on the other. The ambiguities
experienced during the selection of the electrolytic parameters for dressing, the lack of knowledge
of wear mechanism of the ELID-grinding wheels, etc., are reducing the wide spread use of the
ELID process in the manufacturing industries.
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Principle ELID
Electrolysis is a process where electrical energy is converted into chemical energy. The
process happens in an electrolyte, which gives the ions a possibility to transfer between two
electrodes. The electrolyte is the connection between the two electrodes which are also connected
to a direct current as illustrated in Figure 2.1, and the unit is called the electrolyze cell. When
electrical current is supplied, the positive ions migrate to the cathode while the negative ions
will migrate to the anode. Positive ions are called cations and are all metals. Because of their
valency they lost electrons and are able to pick up electrons. Anions are negative ions. They carry
more electrons than normal and have the opportunity to give them up. If the cations have contact
with the cathode, they get the electrons they lost back to become the elemental state. The anions
react in an opposite way when they contact with the anode. They give up their superfluous
electrons and become the elemental state. Therefore the cations are reduced and the anions are
oxidized. To control the reactions in the electrolyze cell various electrolytes (the electrolyte
contains the ions, which conduct the current) can be chosen in order to stimulate special reactions
and effects. The ELID uses similar principle but the cell is varied by using different anode and
cathode materials, electrolyte and the power sources suitable for machining conditions.
Figure 2.1 Electrolytic cell.
The cell is created using a conductive wheel, an electrode, an electrolyte and a power
supply, which is known as the ELID system. Figure 2.2 shows the schematic illustration of
the ELID system. The metal-bonded grinding wheel is made into a positive pole through the
application of a brush smoothly contacting the wheel shaft. The electrode is made into a
negative pole. In the small clearance of approximately 0.1 to 0.3 mm between the positive
and negative poles, electrolysis occurs through the supply of the grinding fluid and an electrical
current.
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Figure 2.2 Schematic illustration of the ELID system.
The ELID grinding wheels are made of conductive materials i.e. metals such as cast
iron, copper and bronze . The diamond layer is prepared by mixing the metal and the diamond
grits with certain volume percentage, and the wheels were prepared by powder metallurgy. The
prepared diamond layer is attached with the steel hub as shown in Figure 2.3. The
grinding wheels are available in different size and shapes. Among them the straight type and
the cup shape wheels are commonly used.
Figure 2.3 Metal bonded grinding wheel.
* The function of the Electrolyte
The electrolyte plays an important role during in-process dressing. The performance of the
ELID depends on the properties of the electrolyte. If the oxide layer produced during electrolysis
is solvable, there will not be any oxide layer on the wheel surface and the material oxidized from
the wheel surface depends on the Faraday’s law. However, the ELID uses an electrolyte in
which the oxide is not solvable and therefore the metal oxides are deposited on the grinding
wheel surface during in-process dressing. The performance of different electrolytes has been
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studied by Ohmori et al., which shows the importance of the selection of the electrolyte .
The electrolyte is diluted (2%) with water and used as an electrolyte and coolant for grinding.
The amount of chlorine presents in the water should be considered because it has a positive
potential, which has a significant influences on electrolysis.
* Power sources
Different power sources such as AC, DC and pulsed DC have been experimented with
the ELID. The applications and the advantages of different power sources were compared,
and the results were described in the previous studies [Ohmori, 1995, 1997]. However, the
recent developments show that the pulsed power sources can produce more control over the
dressing current than other power sources. When the DC-pulsed power source is used as the
ELID power supply, it is essential to understand the basics of pulsed electrolysis in order to
achieve better performance and control.
*Different methods of ELID.
ELID is classified into four major groups based on the materials to be ground and the
applications of grinding, even though the principle of in-process dressing is similar for all the
methods. The different methods are as follows:
1. Electrolytic In-process Dressing (ELID – I),
2. Electrolytic Interval Dressing (ELID – II),
3. Electrolytic Electrode-less dressing (ELID – III) and
4. Electrolytic Electrode-less dressing using alternate current (ELID – IIIA).
1. Electrolytic In-process Dressing (ELID – I)
This is the conventional and most commonly studied ELID system, where a
separate electrode is used. The basic ELID system consists of an ELID power
supply, a metal-bonded grinding wheel and an electrode. The electrode used could
be 1/ 4 or 1/6 of the perimeter of the grinding wheel. Normally copper or graphite
could be selected as the electrode materials. The gap between the electrode and
the grinding wheel was adjusted up to 0.1 to 0.3 mm. Proper gap and coolant flow
rate should be selected for an efficient in- process dressing. Normally arc shaped
electrodes are used in this type of ELID and the wheel used is either straight type.
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Fig . ELID 1 arrangement for spherical superfinishing
2. Electrolytic Interval Dressing (ELID – II)
Small-hole machining of hard and brittle materials is highly demanded in most of the
industrial fields. The problem in micro-hole machining includes the following:
• Difficult to prepare small grinding wheels with high quality,
• Calculation of grinding wheel wear compensation and
• Accuracy and surface finish of the holes are not satisfactory.
The existing ELID grinding process is not suitable for micro-hole machining because of
the difficulty of mounting of an electrode. Using the combination of sintered metal bonded
grinding wheels of small diameter, Electric Discharge Truing (EDT) and Electrolytic Interval
Dressing (ELID–II) could solve the problems in micro-hole machining. The smallest grinding
wheel for example 0.1 mm can also be trued accurately by using EDT method, which uses
DC-RC electric power. The small grinding wheels can be pre-dressed using electrolysis in order
to gain better grain protrusions. The dressing parameters should be selected carefully to avoid
excessive wear of grinding wheel. The grinding wheel is dressed at a definite interval based on
the grinding force. If the grinding force increases beyond certain threshold value, the wheel is re-
dressed.
3. Electrode-less In-process dressing (ELID– III)
Grinding of materials such as steel increases the wheel loading and clogging due to the
embedding of swarf on the grinding wheel surface and reduces the wheel effectiveness. If the size
of swarf removal is smaller, the effectiveness of the grinding wheel increases. For machining
conductive materials like hardened steels, metal-resin-bonded grinding wheels have been used.
The conductive workpiece acts as the electrode and the electrolysis occurs between the grinding
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wheel and the work piece. Normally the bonding material used for grinding wheel is copper or
bronze. The electrolytic layer is formed on the work piece and it is removed by the diamond grits.
Thus the swarf production is controlled by using electrode-less in-process dressing (ELID–III).
During electrolytic dressing, the base material is oxidized and the wheel surface contains resin and
diamond grits. Theoretically the metal bond is removed by electrolysis, but the experimental
results showed that the grinding wheel surface contains cavities, which is caused due to electric
discharge. When high electric parameters are elected, the amount of electric discharge increases
and it causes damage on both the wheel and ground surfaces. For better surface finish, low voltage,
low current, low duty ratio and low in- feed rate should be selected.
4. Electrode-less In-process dressing using alternative current (ELID–IIIA)
The difficulties of using electrode-less in-process dressing could be eliminated with the
application of ELID-IIIA. The alternative current produces a thick oxide layer film on the surface
of the workpiece, which prevents the direct contact between the grinding wheel and the workpiece.
Thus the electric discharge between the wheel and workpiece is completely eliminated and the
ground surface finish is improved.
The concept of the ELID is to provide uninterrupted grinding using harder metal-bonded
wheels. The problems such as wheel loading and glazing can be eliminated by introducing
an ‘electrolyze cell’ (anode, cathode, power source and electrolyte) during grinding, which
stimulates electrolysis whenever necessary. The electrolyze cell required for the in-process
dressing is different from the cell used for standard electrolysis or electroplating. Therefore,
attention should be focused on the selection of factors such as the bond-material for the grinding
wheels, electrode material, the electrolyte and the power source. If any one of the parameters is
not chosen properly, the result obtained from the electrolysis will be different. Therefore, an
adequate knowledge about the electrolysis is necessary before incorporate with the machining
process. This chapter provides the necessary information about the ELID, selection of bond
material for the ELID, the electrode material selection for the grinding wheels, electrolyte and the
power source selections.
Application The structural ceramic components
Bearing steel
Chemical vapor deposited silicon carbide (CVD- SiC)
Precision internal grinding
Mirror surface finish on optical mirrors
Micro lens
Form grinding
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Die materials
Precision grinding of Ni-Cr-B-Si composite coating
Micro-hole machining
ELID-lap grinding
Grinding of silicon wafers
3. Electrochemical Grinding
Electrochemical grinding (ECG) utilizes a negatively charged abrasive grinding wheel,
electrolyte solution, and a positively charged work- piece, as shown in Fig. 3.1. The process is,
therefore, similar to ECM except that the cathode is a specially constructed grinding wheel instead
of a cathodic shaped tool like the contour to be machined by ECM. The insulating abrasive material
(diamond or aluminum oxide) of the grinding wheel is set in a conductive bonding material. In
ECG, the nonconducting abrasive particles act as a spacer between the wheel conductive bond and
the anodic workpiece. Depending on the grain size of these particles, a constant interelectrode gap
(0.025 mm or less) through which the electrolyte is flushed can be maintained.
Figure 3.1 Surface ECG
The abrasives continuously remove the machining products from the working area. In the machining system shown in Fig. 3.2, the wheel is a rotating cathodic tool with abrasive particles (60–320 grit number) on its periphery. Electrolyte flow, usually NaNO3, is provided for ECD. The wheel rotates at a surface speed of 20 to 35 m/s, while current rat- ings are from 50 to 300A.
Material removal rate
When a gap voltage of 4 to 40 V is applied between the cathodic grind- ing wheel and the anodic workpiece, a current density of about 120 to 240 A/cm2 is created. The current density depends on the material being machined, the gap width, and the applied voltage. Material is mainly removed by ECD, while the MA of the abrasive grits accounts for an additional 5 to 10 percent of the total material removal.
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Figure 3.2 ECG machining system components.
Removal rates by ECG are 4 times faster than by conventional grind- ing, and ECG always
produces burr-free parts that are unstressed. The volumetric removal rate (VRR) is typically 1600
mm3/min. McGeough (1988) and Brown (1998) claimed that to obtain the maximum removal
rate, the grinding area should be as large as possible to draw greater machining current, which
affects the ECD phase. The volumetric removal rate (mm3/min) in ECG can be calculated using
the following equation:
VRR = εI ρF
where e = equivalent weight, g I = machining current, A r = density of workpiece material, g/mm3 F = Faraday’s constant, C
ECG is a hybrid machining process that combines MA and ECD. The machining rate,
therefore, increases many times; surface layer prop- erties are improved, while tool wear and
energy consumption are reduced. While Faraday’s laws govern the ECD phase, the action of the
abrasive grains depends on conditions existing in the gap, such as the electric field, transport of
electrolyte, and hydrodynamic effects on boundary layers near the anode. The contribution of
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either of these two machining phases in the material removal process and in surface layer formation
depends on the process parameters. Figure 3.3 shows the basic components of the ECG process.
The contribution of each machining phase to the material removal from the workpiece has resulted
in a considerable increase in the total removal rate QECG, in relation to the sum of the removal
rate of the electrochemical process and the grinding processes QECD and QMA, when keeping
the same values of respective parameters as during the ECG process.
Figure 3.3 ECG process components.
Fig. 3.4, the introduction of MA, by a rotary conductive abrasive wheel, enhances the ECD
process. The work of the abrasive grains performs the mechanical depolarization by abrading
the possible insoluble films from the anodic workpiece surface. Such films are especially formed
in case of alloys of many metals and cemented carbides. A specific purpose of the abrasive grains
is, therefore, to depassivate mechanically the work- piece surface. In the machining zone there
is an area of simultaneous ECD and MA of the workpiece surface, where the gap width is less
than the height of the grain part projecting over the binder. Another area of pure
electrochemical removal where the abrasive grains do not touch the workpiece surface exists at
the entry and exit sides of the wheel.
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Figure 3.4 ECD and MA in the machining gap during ECG.
Process Characteristics
1. The life of grinding wheel in ECG process is very high as around 90% of the metal is removed
by electrolysis action and only 10% is due to the abrasive action of the grinding wheel.
2. The ECG process is capable of producing very smooth and burr free edges unlike those formed
during the conventional grinding process (mechanical).
3. The heat produced in the ECG process is much less, leading to lesser distortion of the workpiece.
4. The major material removal activity in ECG process occurs by the dissolving action through the
chemical process. There is very little tool and workpiece contact and this is ideally suited for
grinding of the following categories:
5. Fragile work-pieces which otherwise are very difficult to grind by the conventional process
6. The parts that cannot withstand thermal damages and
7. The parts designed for stress and burr free applications.
Applications
The ECG process is particularly effective for
1. Machining parts made from difficult-to-cut materials, such as sintered carbides, creep-resisting
(Inconel, Nimonic) alloys, titanium alloys, and metallic composites.
2. Applications similar to milling, grinding, cutting off, sawing, and tool and cutter sharpening.
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3. Production of tungsten carbide cutting tools, fragile parts, and thin- walled tubes.
4. Removal of fatigue cracks from steel structures under seawater. In such an application holes
about 25 mm in diameter, in steel 12 to25 mm thick, have been produced by ECG at the ends of
fatigue cracks to stop further development of the cracks and to enable the removal of specimens
for metallurgical inspection.
5. Producing specimens for metal fatigue and tensile tests.
6. Machining of carbides and a variety of high-strength alloys.
The ECG process can be applied to the following common methods of grinding
1. face wheel grinding,
2. cone wheel grinding,
3. peripheral or surface grinding,
4. form wheel or square grinding.
The process is not adapted to cavity sinking, and therefore it is unsuitable for the die-
making industry.
Advantages
■ Absence of work hardening
■ Elimination of grinding burrs
■ Absence of distortion of thin fragile or thermo sensitive parts
■ Good surface quality
■ Production of narrow tolerances
■ Longer grinding wheel life
Disadvantages
■ Higher capital cost than conventional machines
■ Process limited to electrically conductive materials
■ Corrosive nature of electrolyte
■ Requires disposal and filtering of electrolyte
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4. Elctro-Chemical Etching (ECE)
Etching.
This is the material removal step. The part is immersed in an etchant that chemically attacks those
portions of the part surface that are not masked. The usual method of attack is to convert the work material
(e.g. a metal)into a salt that dissolves in the etchant and is there by removed from the surface. When the
desired amount of material has been removed, the part is withdrawn from the etchant and washed to stop
the process. Etching is usually done selectively, by coating surface areas that are to be protected and leaving
other are as exposed for etching. The coating may be an etch-resistant photoresist, or it may be a previously
applied layer of material such as silicon dioxide.
There are two main categories of etching process in semiconductor processing: wet
chemical etching and dry plasma etching. Wet chemical etching is the older of the two processes
and is easier to use. However, there are certain disadvantages that have resulted in growing use of
dry plasma etching.
1. Wet chemical etching :-
Wet chemical etching involves the use of an aqueous solution, usually an acid, to etch away
a target material. The etching solution is selected because it chemically attacks the specific material
to be removed and not the protective layer used as a mask. In its simplest form, the process can be
accomplished by immersing the masked wafers in an appropriate etchant for a specified time and
then immediately transferring them to a thorough rinsing procedure to stop the etching. Process
variables such as immersion time, etchant concentration, and temperature are important in
determining the amount of material removed.
Figure 4.1 Profile of a properly etched layer
A properly etched layer will have a profile as shown in Figure 4.1. Note that the etching
reaction is isotropic (it proceeds equally in all directions), resulting in an undercut below the
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protective mask. Perfectly anisotropic etching occurs in only one direction. In general, wet
chemical etching is isotropic, and so the mask pattern must be sized to compensate for this effect.
Note also that the etchant does not attack the layer below the target material in our
illustration. In the ideal case, an etching solution can be formulated that will react only with the
target material and not with other materials in contact with it. In practical cases, the other materials
exposed to the etchant maybe attacked but to a lesser degree than the target material. The etch
selectivity of the etchant is the ratio of etching rates between the target material and some other
material, such as the mask or substrate material. For example, etch selectivity of hydrofluoric acid
for SiO2 over Si is infinite. If process control is inadequate, either under-etching or over-etching
can occur, as in Figure 4.1. Under etching, in which the target layer is not completely removed,
results when the etching time is too short and/or the etching solution is too weak. Over-etching
involves too much of the target material being removed, resulting in loss of pattern definition and
possible damage to the layer beneath the target layer. Over-etching is caused by overexposure to
the etchant.
Advantages
- Low Cost
- Reliability
- High Throughput
- Excellent Selectivity
Disadvantage
- Very hard to control Critical feature Dimension
- Difficult to control the degree of overetching due to undercut
- Decrease in Etch rate as Reagent solutions are consumed
- Hazardous and Difficult to handle
- Toxic Fume
Applications of Wet Process
- Silicon Oxide Etch
SiO2 + 6HF ® H2SiF6 + 2H2O
HF : Etchant, NH4F : Buffering Agent
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- Poly-Si Etch
Si + HNO3 + 6HF ® H2SiF6 + HNO2 + H2 + H2O
HNO3 : Oxidant, HF : Etchant, CH3COOH : Buffering Agent
- Al Etch
HNO3 : Oxidant, H3PO4 : Etchant
- Silicon Nitiride Etch
Hot (>150°C) H3PO4 : Etchant
2. Dry Plasma Etching :-
This etching process uses an ionized gas to etch a target material. The ionized gas is created
by introducing an appropriate gas mixture into a vacuum chamber and using radio frequency (RF)
electrical energy to ionize a portion of the gas, thus creating a plasma.
FIGURE 4.2, Two problems in etching: (a) under-etching and (b) over-etching.
The high-energy plasma reacts with the target surface, vaporizing the material to remove
it. There are several ways in which a plasma can be used to etch a material; the two principal
processes in IC fabrication are plasma etching and reactive ion etching.
In plasma etching, the function of the ionized gas is to generate atoms or molecules that
are chemically very reactive, so that the target surface is chemically etched upon exposure. The
plasma etchants are usually based on fluorine or chlorine gases. Etch selectivity is generally more
of a problem in plasma etching than in wet chemical etching. For example, etch selectivity for
SiO2 over Si in a typical plasma etching process is 15 at best, compared with infinity with HF
chemical etching.
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FIGURE 4.3, (a) A fully anisotropic etch, with A=1; and (b) a partially anisotropic
etch, with A=approximately 1.3.
An alternative function of the ionized gas can be to physically bombard the target material,
causing atoms to be ejected from the surface. This is the process of sputtering, one of the
techniques in physical vapor deposition. When used for etching, the process is called sputter
etching. Although this form of etching has been applied in semiconductor processing, it is much
more common to combine sputtering with plasma etching as described in the preceding, which
results in the process known as reactive ion etching. This produces both chemical and physical
etching of the target surface.
The advantage of the plasma etching processes over wet chemical etching is that they are
much more anisotropic. This property can be readily defined with reference to Figure 4.3. In (a),
a fully anisotropic etch is shown; the undercut is zero. The degree to which an etching process is
anisotropic is defined as the ratio:
A=d / u…………………………………… (1)
Where A=degree of anisotropy; d=depth of etch, which in most cases will be the thickness of the
etched layer; and u = the undercut dimension, as illustrated in Figure 4.3(b). Wet chemical etching
usually yields A values around 1.0, indicating isotropic etching.
Plasma etching and reactive ion etching have high degrees of anisotropy, but below those
achieved in sputter etching. As IC feature sizes continue to shrink, anisotropy becomes
increasingly important for achieving the required dimensional tolerances.
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3. Chemical Etching
Chemical etching is done by free radicals.
Free radicals are neutral molecules that have incomplete bonding (unpaired
electrons)
For example,
eFCFCFe 34
Both F and CF3 are free radicals.
Both are highly reactive.
F wants 8 electrons rather than 7 and reacts quickly to find a shared electron.
The idea is to get the free radical to react with the material to be etched (Si, SiO2).
The byproduct should be gaseous so that it can be transported away.
The reaction below is such a reaction,
4SiFSi4F
Thus, we can etch Si with CF4.
There are often several more complex intermediate states.
Gas additives can be used to increase the production of the reactive species (O2 in CF4)
The chemical component of plasma etching occurs isotropically.
This is because,
- The arrival angles of the species is isotropic
- There is a low sticking coefficient (which is more important)
The arrival angle follows what we did in deposition and there is a cosn dependence
where n=1 is isotropic
The sticking coefficient is,
incident
reactedc
F
FS
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Fig 4.4 Process involved in chemical etching during plasma etch process
A high sticking coefficient means that the reaction takes place the first time the ion
strikes the surface.
For lower sticking coefficients, the ion can leave the surface (usually at random angles)
and strikes the surface somewhere else.
One would guess that the sticking coefficient for reactive ions is high
However, there are often complex reactions chained together. This complexity often
means low sticking coefficients
Sc for O2/CF4 on Si is about 0.01
This additional “bouncing around” of the ions leads to isotropic etching.
Since free radicals etch by chemically reacting with the material to be etched, the
process can be highly selective
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Advantages
- Isotropic
- Purely Chemical Reaction
- High Pressure
- Batch Wafer Type
- Less Electrical Damage
- Doesn’t require as high doping level as boron
-Better thickness control
-Less stress on wafer
- Batch fabrication *(Electrodless)
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5.0 ELECTRO JET MACHINING
ELECTRO JET DRILLING
Introduction
Demands of small size machines have directed our attention to nontraditional techniques .
EJD is Non-traditional method Micro level hole drilling . Use in cooling holes in jet turbine blades,
printed circuit board, inkjet printer head, surgical implants.
Working
EJD is a non-conventional machining process in which a negatively charged stream of
acid electrolyte is impinged on the workpiece to form a hole. The acid electrolyte (10-25%
concentration) is passed under pressure (0.3-1.0 N/mm2 ) through a finely drawn glass tube nozzle.
The electrolyte jet gets charged when a platinum wire, inserted into the glass tube is connected to
the negative terminal of DC power supply. The workpiece acts as anode. When a suitable electric
potential is applied across the two electrodes, the material removal takes place through electrolytic
dissolution as the charged electrolyte stream strikes the workpiece. The metal ions thus removed
from the work surface are carried away with the flow of the electrolyte. A much longer and thinner
electrolyte flow path requires much higher voltage (150-750V) so as to effect sufficient current
flow.
1: DC Power supply; 10: Pump;
2: Nozzle manifold; 11: Filter;
3: Microprocessor; 12: Electrolyte tank;
4: Stepper motor; 13: Screw pump;
5: Glass tube nozzle; 14: Speed variator; 6: Workpiece; 15:Pump motor.
7:Perspex enclosure;
8: Pressure gauge;
9: Electrolyte tank;
Fig.1 Schematic of experimental setup for electro jet drilling
For each particular run, the specified input parameters were set and through hole were
machined. Completion of hole was marked by the exit of the jet through the workpiece. The time
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taken for machining a through hole was recorded by an electronic timer. An electronic balance
(Metler, LC: 0.1mg) was used to weigh the workpiece before and after drilling. The rate of
machining was determined using equation (1). The hole size measurements were taken using
Toolmakers microscope. A total of three diameter measurements were made at hole orientations
60 degree apart and averaged values were used in calculations. The radial overcut was determined
using equation (2). Based on the entry side hole diameter and exit side hole diameter
measurements, the hole taper was calculated using the equation (3).
Fig 2. Working Principle
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MRR
Applied Voltage – As voltage increases-current increases-MRR increases(Faraday’s Law) –
Increases rapidly above 350 V
Electrolyte Conc. – Increase in electrolytes conc. –increases MRR –because it increases
conductivity –more amount of current flow
Feed rate – Increase in FR-reduces inter electrode gap- leads to smaller ohmic resistance-inc
electrolyzing current.
Overcut
Applied Voltage – Increases in applied voltage- greater overcut
Electrolyte Conc. – Increase in electrolytic conc.-greater overcut •
Feed Rate – Higher feed rate-less radial overcut-because less interaction time
Current – Inc. in current-increases overcut
Hole Taper
Hole taper –depends on diff. between hole entrance diameter and hole exit diameter.
Increasing applied voltage and electrolyte concentration- results in greater hole taper - reasons
for this is that the electro jet remains in contact with the entry side of the workpiece for a
maximum period of time resulting in a larger hole entrance diameter than the hole exit
diameter.
Advantages – Micro-level holes can be made.
– Applied on hard and brittle material
– Material are removed easily
– Less costly than traditional drilling
Disadvantages
– Set up should not vibrate otherwise hole will get large or deform.
– More maintenance
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6.0 Laser based Heat Treatment
Laser beam (LB) heating uses a high-intensity beam of coherent light focused on a small
area. The beam is usually moved along a defined path on the work surface, causing heating of the
steel into the austenite region. When the beam is moved, the area is immediately quenched by
heat conduction to the surrounding metal. Laser is an acronym for light amplification by
stimulated emission of radiation. The advantage of LB over Electron beam EB heating is that
laser beams do not require a vacuum to achieve best results. Energy density levels in Electron
beam (EB) and LB heating are lower than in cutting or welding.
Laser beam technology has led to the possibility of localized modifications to the
microstructures of a range of materials. Such modifications can lead to improved service
properties in the surface layers of a component, while leaving the bulk properties essentially
unchanged. There are number of mechanisms by which these changes can be brought about, but
all depend on the ability to manipulate the laser beam accurately, and on the high power density
of the beam. The common advantages of laser surfacing compared to alternative processes are:
• Chemical cleanliness and cosmetic appearance
• Minimal heat input, since the source temperature is so high, transformation occurs so
quickly and the heat input to the part is very low. This reduces the distortion and the heat-
affected zone is very small.
• No post machining required
• Non-contact process
• Ease of integration
LASER HEAT TREATMENT PRINCIPLES
The principles of laser heating are similar to those of conventional through heating. The
time scales involved in the former are, however, typically an order of magnitude shorter. Whereas
heating is conventionally induced by a furnace, flame, arc or induction coil, the laser beam is
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focused or shaped into a suitable pattern and scanned over the component. The high energy density
laser beam heats the surface much more rapidly, reducing the time for conduction into the bulk of
the component. Laser heat treatment and surfacing techniques must complete directly with a wide
range of comparatively low cost conventional processes and must therefore offer significant
advantages.
The laser emits a beam of energy, in the form of either continuously or pulsed. The power
of the beam and the diameter of the focused laser beam can be combined to give one laser
parameter, the power density. The second and other parameter of laser treatment is the rate at
which the power density is moved across a surface. This is often expressed as the interaction time,
i.e. the length of time that the laser beam is focused on any one point on the surface. Figure 1.
shows a range of laser material processes that can occur at different power densities and interaction
time and Figure 2. shows a modified version representing only the heat treatment processes.
Figure 1: Range of laser processes mapped against power density and interaction tine
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Figure 2: Laser heat-treating regimes
Materials of high hardenability may be processed with lower power density and a higher
interaction time, in order to achieve a homogeneous case with significant depth. Materials with
low hardenability are processed with higher power density and lower interaction times in order to
generate the rapid cooling rates required for martensite formation at expense of a shallower case.
Laser sources Currently four different type of laser sources i.e. CO 2, lamp and diode pumped Nd: YAG
and high power diode lasers are being used for laser heat- treatment applications. Until about 10
years ago, only CO2 laser beams were able to deliver the combination of power density and
interaction time necessary for laser heat treatment. The development of multikilowatt Nd: YAG
lasers with both flash lamp and diode pumping provide an alternative source, with several
advantages. One of the main advantage of the Nd: a YAG laser source is that the wavelength of
the laser light (1.06 µm) allows the beam to be delivered via an optical fiber with relatively small
energy losses. This allows flexible delivery of the laser beam at the processing head. Consequently,
Nd: YAG lasers providing high levels of laser power can be manipulated using robot , making
them ideal for three- dimensional processing.
As the beam wavelength decreases i.e. 1.06µm compared to 10.6µm for CO 2 laser, the
absorptivity of metal surfaces increases, and so an absorptive coating is no longer necessary, thus
simplifying the operation considerably. More recently, multikilowatt diode lasers have been
developed with wavelength of 0.8µm, which are compact and can be mounted directly on a robot
for hardening of complex geometry components.
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Beam shape
A round beam is often used for hardening with CO 2 and Nd: YAG laser beams. This is
created by simply defocusing the beam, and is a satisfactory solution for many engineering
applications. The depth profile of hardened region can be approximated as the mirror image of the
beam intensity distribution, with reduced amplitude and some rounding of the edges resulting from
lateral heat flow. By using beam shaping optics, the shape of the hardened sections can be varied
and may be possible to harden with higher coverage rates. If a uniform depth profile of constant
width is needed, a kaleidoscope is the cheapest solution.
PROCESS PARAMETERS
1. Shield gas
Shield gas serves two functions in laser heat treatments. It shields the heated/melt
zone from oxidation and also protects the focusing optics from the fumes. Argon and nitrogen
shield gases are normally used and typical flow rates are around 20l/min. The flow rate will depend
on the method of shielding and also diameter of nozzle that is being used to deliver the gas.
2. Feed rate
The length of the beam in the travel direction is fixed by the power density and track width
requirements. A power level in the range 1-4kW is normally used. A high power enables high feed
rate (Figure 6) to be used, with correspondingly high coverage rates. However, the practical range
that can be used considerably as risk of both overheating, leading to surface melting or an
insufficient peak temperature with no hardening. Feed rate is the variable that is normally changed
when fine-tuning the process in order to achieve the required hardened depth and degree of
homogenization.
System basics Three elements that make up a basic laser processing sys- tem are materials handling,
motion and controls, and the laser light source. These sys- tem elements are not unique when
considering many materials processing cells used in industry today. Compared with prime
competitors of laser technology, such as induction and flame hardening systems, the only
fundamental change is the use of a laser for the energy source.
As with many other materials processing systems, materials handling is a major
consideration in a laser-treating system. The issue is more than just getting parts in and out, as the
economics of moving parts from one position to another can be a significant factor. From manual
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systems used in job shops to complete automation on the manufacturing floor, the cost of materials
handling can exceed that of motion and control and the laser combined. When considering a laser
system, it is important to determine as closely as possible what the laser “on-time” is for a
particular product. The laser should be used to treat parts at a duty cycle of 75% or bet- ter. Because
typical cycles range between less than a second to as long as 30 minutes, each application provides
unique challenges.
Motion and control for laser systems often is more sophisticated than that required for
competing technologies. Lasers are ideally suited to computer control, capable of being turned on
and off in a matter of milliseconds. It is not unusual for a laser process to be con- trolled to one-
tenth of a second. Such accuracy requires close control of both of time and position.
Many cutting and welding systems are accurate to 0.001 in. (0.02 mm) and repeatable to
0.0005 in. (0.01 mm). Although most heat treating applications do not require such close control,
the potential exists to treat parts small- er than the head of a pin with accuracy and repeatability.
Besides providing exceptional control, laser hardening systems provide flexibility in that
changeover to another product often can be performed simply by selecting a new pro- gram and
exchanging tooling. Selection of the type of laser, the third basic element of a system, can be
difficult for those not familiar with the technology. The many avail- able choices boil down to
three basic technologies: car- bon dioxide (CO2) lasers, neodymium: yttrium-aluminum-garnet
(Nd:YAG) lasers, and high-power direct diode (HPDD) lasers. The likely choice was CO2 until as
recently as five years ago. However, a wider choice due the commercial availability of both high-
power Nd:YAG and HPDD lasers over the past several years has complicated the selection
process.
Lasers used for heat treating have wavelengths that fall between 800 and 10,600 nm. Over
this range of wavelengths, iron has nearly a four fold increase in absorption. Because of such poor
absorption at longer wavelengths, it is necessary to modify the surface condition of a part to
efficiently absorb light. This can be done by roughening the surface, but the most common method
is to apply an absorptive coating such as paints, inks, phosphates, oxides and oxyacetylene soot.
Workpiece temperature also affects absorption in favor of laser heat treating. Results show that
using a wavelength of 1,060 nm, absorption by steel during laser heat treatment is approximately
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60% and can be improved to 85% by the addition of a suitable coating. At 10,600 nm, absorption
can exceed 70% when coatings are applied to a surface. Coating application can be automated and
performed in the laser cell with little to no drying time, as in the case of paints, or it can be applied
in advance. Because of costs associated with the application and removal of coatings, the shorter
wavelength light sources are attractive to many use.
Application
Automotive and machine tool industries have been responsible for much of the laser heat-
treatment process development and some of the applications are listed in the Table 1.
Table 1: Few industrial application of laser transformation hardening
**********Thank You**********
