BE Elective Subject

1. Mechanical Engineering
SPPU
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2. Syllabus
Unit I: Metal Forming
Roll forming, High velocity hydro forming, High velocity Mechanical Forming,
Electromagnetic forming, High Energy Rate forming (HERF), Spinning, Flow forming,
Shear Spinning
Unit II: Advanced Welding, casting and forging processes
Friction Stir Welding – Introduction, Tooling, Temperature distribution and resulting melt
flow Advanced Die Casting - Vacuum Die casting, Squeeze Casting
Unit III: Advanced techniques for Material Processing
STEM: Shape tube Electrolytic machining, EJT: Electro Jet Machining, ELID:
Electrolytic Inprocess Dressing, ECG: Electrochemical Grinding, ECH: Elctro-chemical
Etching Laser based Heat Treatment
Unit IV: Micro Machining Processes
Diamond micro machining, ultrasonic micro machining, micro electro discharge
machining
Unit V: Additive Manufacturing Processes
Introduction and principles, Development of additive manufacturing Technologies,
general additive manufacturing processes, powder based fusion process, extrusion based
system, sheet lamination process, direct write technologies
Unit VI: Measurement Techniques in Micro machining
Introduction, Classification of measuring System, Microscopes : Optical
Microscope, Electron Microscopes, Laser based System, Interference Microscopes
and comparators, Surface profiler, Scanning Tunneling Microscope, Atomic force
micro scope, Applications.
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3. UNIT 1.
ADVANCED MANUFACTURING PROCESS
Metal
Forming
Semester VII – Mechanical Engineering SPPU
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Unit.1 AMP
1.Roll forming
2.High velocity hydro forming,
3.High velocity Mechanical Forming,
4.Electromagnetic forming,
5.High Energy Rate forming (HERF),
6.Spinning,
7.Flow forming,
8.Shear Spinning
Insem-Aug.2015-6M
Rolling is a deformation process in which the thickness of the work is reduced by
compressive forces exerted by two opposing rolls. The rolls rotate as illustrated in Figure
1. to pull and simultaneously squeeze the work between them. The basic process shown in
our figure 1. is flat rolling, used to reduce the thickness of a rectangular cross section. A
closely related process is shape rolling, in which a square cross section is formed into a
shape such as an I-beam. Most rolling processes are very capital intensive, requiring
massive pieces of equipment, called rolling mills, to perform them. The high investment
cost requires the mills to be used for production in large quantities of standard items such
as sheets and plates. Most rolling is carried out by hot working, called hot rolling, owing
to the large amount of deformation required. Hot-rolled metal is generally free of residual
stresses, and its properties are isotropic. Disadvantages of hot rolling are that the product
cannot be held to close tolerances, and the surface has a characteristic oxide scale. Steel
making provides the most common application of rolling mill operations. Let us follow the
sequence of steps in a steel rolling mill to illustrate the variety of products made. Similar
steps occur in other basic metal industries. The work starts out as a cast steel ingot that has
METAL FORMING
Content
s
1.Roll Forming

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just solidified. While it is still hot, the ingot is placed in a furnace where it remains for
many hours until it has reached a uniform temperature throughout, so that the metal will
flow consistently during rolling. For steel, the desired temperature for rolling is around
1200 C (2200F). The heating operation is called soaking, and the furnaces in which it is
carried out are called soaking pits.
From soaking, the ingot is moved to the rolling mill, where it is rolled into one of three
intermediate shapes called blooms, billets, or slabs. Abloom has a square cross section 150 mm
(6 in) or larger. A slab is rolled from an ingot or a bloom and has a rectangular cross section of
width 250 mm (10 in) or more and thickness 40 mm (1.5 in) or more. A billet is rolled from a
bloom and is square with dimensions 40 mm (1.5 in) on a side or larger. These intermediate shapes
are subsequently rolled into final product shapes. Blooms are rolled into structural shapes and rails
for railroad tracks. Billets are rolled into bars and rods. These shapes are the raw materials for
machining, wire drawing, forging, and other metalworking processes. Slabs are rolled into plates,
sheets, and strips. Hot-rolled plates are used in shipbuilding, bridges, boilers, welded structures for
various heavy machines, tubes and pipes, and many other products. Figure 3. shows some of these
rolled steel products. Further flattening of hot-rolled plates and sheets is often accomplished by
cold rolling, in order to prepare them for subsequent sheet metal operations. Cold rolling
strengthens the metal and permits a tighter tolerance on thickness. In addition, the surface of the
cold-rolled sheet is absent of scale and generally superior to the corresponding hot-rolled product.
These characteristics make cold-rolled sheets, strips, and coils ideal for stampings, exterior panels,
and other parts of products ranging from automobiles to appliances and office furniture.
Fig.3.0. Rolling Process
Roll forming is one of the most common techniques used in the forming process, to obtain a
product as per the desired shape. The roll forming process is mainly used due to its ease to be
formed into useful shapes from tubes, rods, and sheets. In this process, sheet metal, tubes, strips
are fed between successive pairs of rolls, that progressively bent and formed, until the desired
shape and cross section are attained. The roll forming process adds strength and rigidity to
lightweight materials, such as aluminum, brass, copper and zinc, composites. Roll forming
processes are successfully used for materials that are difficult to form by other conventional

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methods because of the spring back, as this process achieves plastic deformation without the
spring back. In addition, the roll forming improves the mechanical properties of the material,
especially, its hardness, grain size, and also increases the corrosion rate.
Rolling is the most extensively used metal forming process and its share is roughly
90% process. The material to be rolled is drawn by means of friction into the two revolving roll
gap.The compressive forces applied by the rolls reduce the thickness of the material or changes its
cross sectional thickness of the material .The geometry of the product depend on the contour of
the roll gap.Roll materials are cast iron, cast steel and forged steel because of high strength and
wear resistance. Hot rolls are generally rough so that they can bite the work, and cold rolls are
ground and polished for good finish.In rolling the crystals get elongated in the rolling direction.
Flat rolling is illustrated in Figures 3.0 and .3.1. It involves the rolling of slabs, strips, sheets, and
plates—workparts of rectangular cross section in which the width is greater than the thickness. In
flat rolling, the work is squeezed between two rolls so that its thickness is reduced by an amount
called the draft. Draft is sometimes expressed as a fraction of the starting stock thickness, called
the reduction. In addition to thickness reduction, rolling usually increases work width. This is
called spreading and it tends to be most pronounced with low width-to-thickness ratios and low
coefficients of friction.
Fig3.1.Some of the steel products made in a rolling mill.

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Rolling is the most widely used forming process, which produces products like bloom,
billet, slab, plate, strip, sheet, etc. In order to increase the flowability of the metal during rolling,
the process is generally performed at high temperature and consequently the load requirement
reduces. Friction plays an important role in rolling as it always opposes relative move- ment
between two surfaces sliding against each other. At the point where workpiece enters the roll gap,
the surface speed of the rolls is higher than that of the workpiece. So, the direction of friction is in
the direction of the workpiece movement and this friction force drags it into the roll gap. During
rolling, velocity of the workpiece increases as material flow rate remains same all throughout the
deformation. Material velocity is equal to the surface speed of the rolls at a plane, called the neutral
plane.
1. Reduced labor and material handling
2. Faster, continuous production with reduced cost-per-piece
3. Greater accuracy, uniformity and consistency throughout both the individual piece and
production lots
4. The rollforming process can incorporate perforating, notching, punching, etc., thus reducing
secondary operations, parts rejections, and related costs.
5. Precision parts facilitate savings in labor and costs
6. Speedier assembly resulting from part uniformity and tighter tolerances
7. Far longer lengths are achievable
8. More surface-friendly for prepainted, precoated and preplated metals
9.Two separate pieces/materials can be simultaneously formed, in a
single operation, to produce a strong composite part
9 (Insem-Aug.2015. 6M)
Hydroforming was developed in the late 1940's and early 1950's to provide a cost effective
means to produce relatively small quantities of drawn parts or parts with asymmetrical or irregular
contours that do not lend themselves to stamping. Virtually all metals capable of cold forming can
be hydroformed, including aluminum, brass, carbon and stainless steel, copper, and high strength
alloys.
In hydroforming, high viscous fluid is used to deform the metal against the complex
shaped die. Since no punch is used in this method, hence, thinning of the sheet metal at the punch
corner does not occur. Hydroforming is of two types; sheet forming and tube forming.
A hydroforming press operates like the upper or female die element. This consists of a
pressurized forming chamber of oil, a rubber diaphragm and a wear pad. The lower or male die
Advantages
.
2. High Velocity Hydro Forming

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element, is replaced by a punch and ring. The punch is attached to a hydraulic piston, and the blank
holder, or ring, which surrounds the punch. The hydroforming process begins by placing a metal
blank on the ring. The press is closed bringing the chamber of oil down on top of the blank. The
forming chamber is pressurized with oil while the punch is raised through the ring and into the the
forming chamber. Since the female portion of this forming method is rubber, the blank is formed
without the scratches associated with stamping. The diaphragm supports the entire surface of the
blank. It forms the blank around the rising punch, and the blank takes on the shape of the punch.
When the hydroforming cycle is complete, the pressure in the forming chamber is released and the
punch is retracted from the finished part.
In hydroforming, fluid pressure acting over a flexible membrane is utilized for
controlling the metal flow. Fluid pressure upto 100 MPa is applied. The fluid pressure on
the membrane forces the sheet metal against the punch more effectively. Complex shapes
can be formed by this process. In tube hydroforming, tubes are bent and pressurized by high
pressure fluid. Rubber forming is used in aircraft industry.
1.Tube Hydro forming :
 Used when a complex shape is needed
 A section of cold-rolled steel tubing is placed in a closed die set
 A pressurized fluid is introduced into the ends of the tube
 The tube is reshaped to the confine of the cavity
 Applications
Automotive industry, sport car industry , shaping of aluminium tubes for bicycle
frames.

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2. SHEET HYDROFORMING
1.Sheet steel is forced into a female cavity by water under pressure from a pump or by
action.
2.Sheet steel is deformed by a male punch, which acts against the fluid under pressure.
Fig. Tube hydro forming

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Fig .Sheet hydro forming

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 APPLICATIONS
 Automotive industry,
 Aerospace-Lighter, stiffer parts,kitchen spoutes.
 ADVANTAGES
 Weight reduction .
 Inexpensive tooling costs and reduced set-up time.
 Reduced development costs.
 Improved structural strength and stiffness.
 Lower tooling cost due to fewer parts.
 Fewer secondary operations (no welding of sections required and holes may be punched
during hydroforming)
 Tight dimensional tolerances and low spring back.
 Shock lines, draw marks, wrinkling, and tearing associated with matched die forming are
eliminated.
 Material thinout is minimized.
 Low Work-Hardening
 Multiple conventional draw operations can be replaced by one cycle in a hydroforming
press.
 Ideal for complex shapes and irregular contours.
 Reduced scrap.
 Disadvantages
 Slow cycle time.
 Expensive equipment and lack of extensive knowledge base for process and tool design .
 Requires new welding techniques for assembly.
( Insem –Aug.2015-6M )
It is a type of high velocity cold forming process for electrically conductive metals most commonly
copper and aluminium. The process is also called magnetic pulse forming, and is mainly used for
swaging type operations, such as fastening fittings on the ends of tubes and crimping the terminal
ends of cables. Other applications of the process are blanking, forming, embossing, and drawing.
The principle of electromagnetic forming of a tubular work piece is shown in Figure.1.4.
The work piece is placed into or enveloping a coil. A high charging voltage is supplied for a short
time to a bank of capacitors connected in parallel. The amount of electrical energy stored in the
3. Electromagnetic Forming

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bank can be increased either by adding capacitors to the bank or by increasing the voltage. When
the charging is complete, which takes very little time, a high voltage switch triggers the stored
electrical energy through the coil. A high – intensity magnetic field is established which induces
eddy currents into the conductive work piece, resulting in the establishment of another magnetic
field. The forces produced by the two magnetic fields oppose each other with the consequence,
that there is a repelling force between the coil and the tubular work piece that causes permanent
deformation of the work piece.Either permanent or expandable coils may be used. Since the
repelling force acts on the coil as well the work, the coil itself and the insulation on it must
be capable of withstanding the force, or else they will be destroyed. The expandable coils are less
costly, and are also preferred when a high energy level is needed. Electro Magnetic forming can
be accomplished in any of the following three types of coils used, depending upon the
operation and requirements.
Figure 1.4 Various applications of electromagnetic forming process (nptel). (i) Compression (ii)
Expansion and (iii) Sheet metal forming.
 A coil used for ring compression is shown in Figure 1.4. (i) This coil is similar in geometry to
an expansion coil. However, during the forming operation, the coil is placed surrounding the
tube to be compressed.

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 A coil used for tube expansion is shown in Figure 1.4. (ii); for an expansion operation, the coil
is placed inside the tube to be expanded.
 A flat coil which consists of a metal strip wound spirally in a plane is shown in Figure 1.4.
(iii); Coils of this type are used for forming of sheet metal.
Two types of deformations can be obtained generally in electromagnetic forming system: (i)
compression (shrinking) and (ii) expansion (bulging) of hollow circular cylindrical work
pieces. When the work piece is placed inside the forming coil, it is subjected to compression
(shrinking) and its diameter decreases during the deformation process. When the work piece
is placed outside the forming coil, it is subjected to expansion (bulging) and its diameter
increases during the deformation process. Either compression, or expansion, and even a
combination of both to attain final shapes can be obtained, with a typical electromagnetic
forming system for shaping hollow cylindrical objects.
 The electromagnetic forming technology has unique advantages in the forming, joining
and assembly of light weight metals such as aluminum because of the improved
formability and mechanical properties, strain distribution, reduction in wrinkling, active
control of spring back, minimization of distortions at local features, local coining and
simple die. The applications of electromagnetic tube compression include, shape joints
between a metallic tube and an internal metallic mandrel for axial or torsional loading,
friction joints between a metallic tube and a wire rope or a non-metallic internal mandrel,
solid state welding between a tube and an internal mandrel of dissimilar metallic
materials, tow poles, aircraft torque tubes, chassis components and dynamic compaction
of many kinds of powders .
The EMF process has several advantages over conventional forming processes. Some of
these advantages are common to all the high rate processes while some are unique to
electromagnetic forming. The advantages include:
1.Improved formability.
2.Wrinkling can be greatly eliminated.
3.Forming process can be combined with joining and assembling even with the dissimilar
components including glass, plastic, composites and other metals.
4.Close dimensional tolerances are possible as spring back can be significantly reduced.
5.Use of single sided dies reduces the tooling costs.
6.Applications of lubricants are greatly reduced or even unnecessary; so, forming can be
used in clean room conditions.

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7. The process provides better reproducibility, as the current passing through the forming coils is
the only variable need to be controlled for a given forming set-up. This is controlled by the amount
of energy discharged.
8.Since there is no physical contact between the work piece and die as compared to the use of a
punch in conventional forming process, the surface finish can be improved.
9. High production rates are possible.
10. It is an environmentally clean process as no lubricants are necessary.
Electromagnetic forming is easy to apply and control, making it very suitable to be
combined with conventional sheet stamping. The practical coil can be designed to deal with the
different requirements of each forming operation.
 Working
The electrical energy stored in a capacitor bank is used to produce opposing magnetic fields
around a tubular work piece, surrounded by current carrying coils. The coil is firmly held
and hence the work piece collapses into the die cavity due to magnetic repelling force, thus
assuming die shape.
Fig. Electro Magnetic Forming

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 Process details/ Steps:
i) The electrical energy is stored in the capacitor bank
ii) The tubular work piece is mounted on a mandrel having the die cavity to produce shape on
the tube.
iii) A primary coil is placed around the tube and mandrel assembly.
iv) When the switch is closed, the energy is discharged through the coil v) The coil produces a
varying magnetic field around it.
vi) In the tube a secondary current is induced, which creates its own magnetic field in the
opposite direction.
vii) The directions of these two magnetic fields oppose one another and hence the rigidly held
coil repels the work into the die cavity.
viii) The work tube collapses into the die, assuming its shape.
 Process parameters:
i) Work piece size
ii) Electrical conductivity of the work material.
iii) Size of the capacitor bank
iv) The strength of the current, which decides the strength of the magnetic field and the force
applied.
v) Insulation on the coil. vi) Rigidity of the coil.
 Advantages:
i) Suitable for small tubes
ii) Operations like collapsing, bending and crimping can be easily done.
iii) Electrical energy applied can be precisely controlled and hence the process is accurately
controlled.
iv) The process is safer compared to explosive forming.
v) Wide range of applications.
 Limitations:
i) Applicable only for electrically conducting materials.

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ii) Not suitable for large work pieces.
iii) Rigid clamping of primary coil is critical.
iv) Shorter life of the coil due to large forces acting on it.
Applications:
i) Crimping of coils, tubes, wires
ii) Bending of tubes into complex shapes.
iii) Bulging of thin tubes.
All modern manufacturing industries focus on a higher economy, increased productivity
and enhanced quality in their manufacturing processes. To enhance the material performance, a
high energy rate forming technique is of great importance to industry, which relies on a long and
trouble free forming process.
High energy rate forming (HERF) is the shaping of materials by rapidly conveying
energy to them for short time durations. There are a number of methods of HERF, based mainly
on the source of energy used for obtaining high velocities. Common methods of HERF are
explosive forming, electro hydraulic forming (EHF) and electromagnetic forming (EMF).
Among these techniques, electromagnetic forming is a high-speed process, using a pulsed
magnetic field to form the work piece, made of metals such as copper and aluminum alloys with
high electrical conductivity, which results in increased deformation, higher hardness, reduced
corrosion rate and good formability. Reduction of weight is one of the major concerns in
the automotive industry. Aluminium and its alloys have a wide range of applications, especially in
the fabrication industries, aerospace, automobile and other structural applications, due to their low
density and high strength to weight ratio, higher ductility and good corrosive resistance.
High energy rate forming methods are gaining popularity due to the various advantages
associated with them. They overcome the limitations of conventional forming and make it possible
to form metals with low formability into complex shapes. This, in turn, has high economic and
environmental advantages linked due to potential weight savings in vehicles. In conventional
forming conditions, inertia is neglected, as the velocity of forming is typically less than 5 m/s,
while typical high velocity forming operations are carried out at work-piece velocities of about
100 m/s.
In this process the high energy released due to explosion of an explosive is
utilized for forming of sheets. No punch is required. A hollow die is used. The sheet
4. High Energy Rate Forming (HERF)

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metal is clamped on the top of the die and the cavity beneath the sheet is evacuated. The
assembly is placed inside a tank filled with water. An explosive material fixed at a
distance from the die is then ignited. The explosion causes shock waves to be generated.
The peak pressure developed in the shock wave is given by:
p = k( /R)a
k is a constant, a is also a constant. R is the stand-off distance. Compressibility of the
medium and its impedance play an important role on peak pressure. If the compressibility
of the medium used is lower, then the peak pressure is higher. If the density of the
medium is higher, the peak pressure of the shock wave is higher. Detonation speeds as
high as 6500 m/s are common. The metal flow is also happening at higherspeed, namely,
at 200 m/s. Strain rates are very high. Materials which do not loose ductility at higher
strain rates can be explosively formed. The stand off distance also determines the peak
pressure during explosive forming. Steel plates upto 25 mm thickness are explosive
formed.
Tubes can be bulged using explosive forming.
Fig. : Explosive Forming
The forming processes are affected by the rates of strain used. Effects of strain rates during
forming:
1. The flow stress increases with strain rates
2. The temperature of work is increases due to adiabatic heating.
3. Improved lubrication if lubricating film is maintained.

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4. Many difficult to form materials like Titanium and Tungsten alloys, can be deformed under
high strain rates.
 Principle / important features of HERF processes:
•The energy of deformation is delivered at a much higher rate than in conventional practice.
• Larger energy is applied for a very short interval of time.
• High particle velocities are produced in contrast with conventional forming process.
• The velocity of deformation is also very large and hence these are also called High Velocity
Forming (HVF) processes.
• Many metals tend to deform more readily under extra fast application of force.
• Large parts can be easily formed by this technique.
• For many metals, the elongation to fracture increases with strain rate beyond the usual metal
working range, until a critical strain rate is achieved, where the ductility drops sharply.
• The strain rate dependence of strength increases with increasing temperature.
• The yield stress and flow stress at lower plastic strains are more dependent on strain rate than
the tensile strength.
• High rates of strain cause the yield point to appear in tests on low carbon steel that do not show
a yield point under ordinary rates of strain.
 Advantages of HERF Processes
1. Production rates are higher, as parts are made at a rapid rate.
2. Die costs are relatively lower.
3. Tolerances can be easily maintained.
4. Versatility of the process – it is possible to form most metals including difficult to form
metals.
5. No or minimum spring back effect on the material after the process.
6. Production cost is low as power hammer (or press) is eliminated in the process. Hence it is
economically justifiable.
7. Complex shapes / profiles can be made much easily, as compared to conventional forming.
8) The required final shape/ dimensions are obtained in one stroke (or step), thus eliminating
intermediate forming steps and pre forming dies.

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9) Suitable for a range of production volume such as small numbers, batches or mass
production.
 Limitations:
i) Highly skilled personnel are required from design to execution.
ii) Transient stresses of high magnitude are applied on the work.
iii) Not suitable to highly brittle materials
iv) Source of energy (chemical explosive or electrical) must be handled carefully.
v) Governmental regulations/ procedures / safety norms must be followed.
vi) Dies need to be much bigger to withstand high energy rates and shocks and to prevent
cracking.
vii) Controlling the application of energy is critical as it may crack the die or work.
viii) It is very essential to know the behavior or established performance of the work metal
initially.
 Applications:
i) In ship building – to form large plates / parts (up to 25 mm thick).
ii) Bending thick tubes/ pipes (up to 25 mm thick).
iii) Crimping of metal strips.
iv) Radar dishes
v) Elliptical domes used in space applications.
vi) Cladding of two large plates of dissimilar metals
Insem-Aug.2015-4M
Spinning, in conventional terms, is defined as a process whereby the diameter of the blank
is deliberately reduced either over the whole length or in defined areas without a change in the
wall thickness.
METAL SPINNING is a term used to describe the forming of metal into seamless,
axisym- metric shapes by a combination of rotational motion and force . Metal spinning typically
involves the forming of axisymmetric components over a rotating mandrel using rigid tools or
rollers. There are three types of metal- spinning techniques that are practiced: manual
(conventional) spinning , power spin- ning , and tube spinning .
 Operation.
5. Spinning

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Fig.Spinning Setup
In manual spinning, a circular blank of a flat sheet, or preform, is pressed against a rotating
mandrel using a rigid tool . The tool is moved either manually or hydraulically over the mandrel
to form the component, as shown in Fig. The forming operation can be performed using several
passes. Manual metal spinning is typically performed at room temperature. However, elevated-
temperature metal spinning is performed for components with thick sections or for alloys
with low ductility. Typical shapes that can be formed using manual metal spinning are
shown in Fig. 1 and Fig 2; these shapes are difficult to form economically using other techniques.
Manual spinning is only economical for low-volume production .It is extensively used for
prototypes or for production runs of less than ~1000 pieces, because of the low tooling costs.
Larger volumes can usually be produced at lower cost by power spinning or press forming.
Fig. 1 Schematic diagram of the manual metal- spinning process, showing the deformation of a
metal disk over a mandrel to form a cone

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 Various components produced by metal spinning
_ Bases, baskets, basins, and bowls
_ Bottoms for tanks, hoppers, and kettles
_ Housings for blowers, fans, filters, and flywheels
_ Ladles, nozzles, orifices, and tank outlets
_ pans, and pontoons
_ Cones, covers, and cups
_ Cylinders and drums
_ Funnels
_ Domes, hemispheres, and shells
_ Rings, spun tubing,
_ Vents, venturis, and fan wheels
Fig. 2. Typical components that can be produced by manual metal spinning. Conical, cylindrical,
and dome shapes are shown. Some product examples include bells, tank ends, funnels, caps,
aluminum kitchen utensils, and light reflectors
 Manual Spinning of Metallic Components
Manual metal spinning is practiced by pressing a tool against a circular metal preform
that is rotated using a lathe-type spinning machine. The tool typically has a work face that is
rounded and hardened. Some of the traditional tools are given curious names that describe their
shape, such as “sheep’s nose” and “duck’s bill.” The first manual spinning machine was
developed in the 1930s. Manual metal spinning involves no significant thinning of the work metal;
it is essentially a shaping technique. Metal spinning can be performed with or without a forming
mandrel. The sheet preform is usually deformed over a mandrel of a predetermined shape,
but simple shapes can be spun without a mandrel. Various mechanical devices and/or levers are
typically used to increase the force that can be applied to the preform. Most ductile metals and
alloys can be formed using metal spinning. Manual metal spinning is generally performed without
heating the workpiece; the preform can also be preheated to increase ductility and/or reduce the
flow stress and thereby allow thicker sections to be formed. Manual metal spinning is used to form

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cups, cones, flanges, rolled rims, and double-curved surfaces of revolution (such as bells).
Typical shapes that can be formed by manual metal spinning are shown in Fig. 3 and 4; these
shapes include components such as light reflectors, tank ends, covers, housings, shields, and
components for musical instruments.
Fig. 3 Photograph of conical components that were produced by metal spinning.
ADVANTAGES
1. Sevaral operation can be performed in one set up.
2. Production cost low.
3. The tooling costs and investment in capital equipment are relatively small (typically, at least
an order of magnitude less than a typical forging press that can effect the same operation).
4. The setup time is shorter than for forging.
5. The design changes in the workpiece can be made at relatively low cost.
DISADVANTAGES
1. Highly skilled operators are required, because the uniformity of the formed part depends to
a large degree on the skill of the operator.
2. Manual metal spinning is usually significantly slower than press forming.
3. The deformation loads available are much lower in manual metal spinning than in press
forming.

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Flow forming is a modernized, improved advanced version of metal spinning, which is
one of the oldest methods of chipless forming. The metal spinning method used a pivoted pointer
to manually push a metal sheet mounted at one end of a spinning mandrel. This method was used
to fabricate axisymmetric, thin‐walled, light‐weight domestic products such as saucepans and
cooking pots.Flow forming is a process whereby a metal blank, a disc or a hollow tube are
mounted on a mandrel which rotates the material to make flow axially by one or more rollers along
the rotating mandrel.
The major difference between spinning and flow forming is, in spinning, the thickness
reduction is very minor and in flow forming the variation in thickness can be maintained at
different places along axial directions.Flow forming means shaping a product of sheet metal, tube
or drawpiece in one are more passes of the forming roll or rolls. The magnitude of wall thinning
depends on the properties of the input material and the number of passes.
Flow Forming is an incremental metal forming technique in which a disk or tube of metal
is formed over a mandrel by one or more rollers using tremendous pressure. The roller deforms
the workpiece, forcing it against the mandrel, both axially lengthening and radially thinning it.
Since the pressure exerted by the roller is highly localized and the material is incrementally formed,
often there is a net savings in energy in forming over drawing processes. Flow forming subjects
the workpiece to a great deal of friction and deformation. These two factors may heat the
workpiece to several hundred degrees if proper cooling fluid is not utilized. Flow forming is often
used to manufacture automobile wheels.
During flow forming, the workpiece is cold worked, changing its mechanical properties,
so its strength becomes similar to that of forged metal.Flow forming, also known as tube spinning,
is one of the techniques closely allied to shear forming.
The two types of flow forming are shown in Fig.1. schematically. The difference is
according to the direction of material flow with respect to direction of motion of tool (roller). If
both are in same direction, then it is forward flow forming and if they are in opposite direction,
then it is backward flow forming. Forward flow forming is suitable for long, high precision thin
6. Flow Forming

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walled components. Backward flow forming is suitable for blanks without base or internal
flange. In forward spinning the roller moves away from the fixed end of the work piece, and the
work metal flows in the same direction as the roller, usually toward the headstock. The main
advantage in forward spinning as compared to backward spinning is that forward spinning will
overcome the problem of distortion like bell-mouthing at the free end of the blank and loss of
straightness. In forward spinning closer control of length is possible because as metal is formed
under the rollers it is not required to move again and any variation caused by the variable wall
thickness of the per- form is continually pushed a head of rollers, eventually be- coming trim metal
beyond the finished length. The disadvantage of forward flow forming is that the Production is
slower in forward spinning because the roller must transverse the finished length of the work piece.
In backward flow forming the mandrel is unsupported. In backward spinning the work piece is
held against a fixture on the head stock, the roller advances towards the fixed end of the work
piece, work flows in the opposite direction. The advantage of backward flow forming over
forward flow forming:
1. The preform is simpler for backward spinning because it slides over the mandrel and
does not require an internal flange for clamping.
2. The roller transverse only 50% of the length of the fi- nished tube in making a
reduction of 50% wall thickness and only 25% of the final, for a 75% reduction. We
can procedure 3 m length tube by using of mandrel.
3. In both the flow forming processes, there is no difference in stress and strain rate.
The major disadvantage of backward tube spin- ning is that backward flow forming is normally
prone to non uniform dimension across the length of the product
In this Process as shown in Fig. a, the metal is displaced axially along a mandrel, while the internal
diameter remains constant. It is usually employed to produce cylindrical components. Most
modern flow forming machines employ two or three rollers and their design is more complex
compared to that of spinning and shear forming machines. The starting blank can be in the form
of a sleeve or cup. Blanks can be produced by deep drawing or forging plus machining to improve
the dimensional accuracy. Advantages such as an increase in hardness due to an ability to cold
work and better surface finish couples with simple tool design and tooling cost make flow forming
a particularly attractive technique for the production of hydraulic cylinders, and cylindrical hollow

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parts with different stepped sections.
Fig.1. Forward & Backward Flow Forming
In flow forming, as shown schematically in Fig. a, the blank is fitted into the rotating
mandrel and the rollers approach the blank in the axial direction and plasticise the metal under the
contact point. In this way, the wall thickness is reduced as material is encouraged to flow mainly
in the axial direction, increasing the length of the workpiece the final component length can be
calculated as,
L1 = L0
S0(di + S0)
S1(di + S1)
Where, L1 is the workpiece length, L0 is the blank length,
S0 is the starting wall thickness, S1 is the final wall thickness
and di is the internal diameter.
Both spinning and flow forming can also be combined to produce complex components.
By rotating mandrel process only cylindrical components can be produced. Wong made
observations in his study on flow forming of solid cylindrical billets, with different types of rollers.
A flat faced roller produces a radial flange and a non orthogonal approach of nosed roller produces
a bulge ahead of the roller.
Forward Spinning
Backward Spinning
Headstock
Mandrel

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 Features
The unique features of the flow forming process allow for innovative, cost-
effective engineering or redesign of your product or part, resulting in the following
features:
1. Traditional multi-piece designs can be formed as a single, seamless piece.
2. Increase mechanical properties, such as tensile/yield strength and hardness.
3. Provide design versatility to produce a unique seamless profile with varying wall
thicknesses.
4. Produce cylindrical, conical, or contoured shapes up to 47" diameter.
5. Typical interior finishes of 15Ra without additional manufacturing steps.
6. High material utilization from near-net shape forming process.
Materials Used in Flow forming
• Stainless Steel, Carbon Steel
• Maraging Steel ,Alloy Steel
• Precipitated Hardened Stainless Steel
• Titanium ,Inconel ,Hastelloy
• Brass , Copper, Aluminum
• Nickel , Niobium
 The advantages are:
1. Low production cost.
2. Very little wastage of material.
3. Excellent surface finishes.
4. Accurate components.
5. Improved strength properties.
6. Easy cold forming of high tensile strength alloys.
7. Production of high precision, thin walled seamless components.

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Insem- Aug. 4M
Before the 1950s, spinning was performed on a simple turning lathe. When new technologies
were introduced to the field of metal spinning and powered dedicated spinning machines were
available, shear forming started its development in Sweden.Shear forming was first used in
Sweden and grew out as spinning.
In shear forming the area of the final component is approximately equal to that of the
blank and little reduction in the wall thickness occurs. Whereas with shear forming, a reduction in
the wall thickness is deliberately induced.
The starting workpiece can be thick walled circular or square blank. Shear forming of thick
walled sheet may require two diametrically opposite roller instead of one needed for light gauge
materials. The profile shape of the final component can be concave, convex or combination of
these two geometries. Fig1. shows examples of products that have been shear formed,
Fig. 1. A shear formed product: a hollow cone with a thin wall thickness
Shear forming, also referred as shear spinning, is similar to metal spinning. In shear spinning the
area of the final piece is approximately equal to that of the flat sheet metal blank. The wall
thickness is maintained by controlling the gap between the roller and the mandrel. In shear forming
a reduction of the wall thickness occurs.
The configuration of machine used in shear forming is very similar to the conventional
spinning lathe, except that it is made more robust as higher forces are generated during shear
forming. Nowadays on modern machines, it is common to use both shear forming and spinning
techniques on the same component. In shear forming, the required wall thickness is achieved by
controlling the gap between the roller and the mandrel so that the material is displaced axially,
parallel to the axis of rotation. Since the process involves only localised deformation, much greater

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deformation of the material can be achieved with lower forming forces as compared with other
processes. In many cases, only a single-pass is required to produce the final component to net
shape. Moreover due to work hardening, significant improvement in mechanical properties can be
achieved.
Operation
The shear forming process is shown in Fig. 1. blank is reduced from the initial thickness So to a
thickness S1 by a roller moving along a cone-shaped mandrel of half angle, α During shear
forming, the material is displaced along an axis parallel to the mandrel’s rotational axis as shown
in fig 2. The inclined angle of the mandrel (sometimes referred to as half-cone angle) determines
the degree of reduction normal to the surface. The greater the angle, the lesser will be the reduction
of wall thickness.
The final wall thickness S1 is calculated from the starting wall thickness S0 and the inclined angle
of the mandrel
α (sine law):
S1= So. sinα
Fig1. Principles of shear forming
1. The mandrel has the interior shape of the desired final component.
2. A roller makes the sheet metal wrap the mandrel so that it takes its shape.

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In shear forming, the starting workpiece can have circular or rectangular cross sections.
On the other hand, the profile shape of the final component can be concave, convex or a
combination of these two.
A shear forming machine will look very much like a conventional spinning machine,
except for that it has to be much more robust to withstand the higher forces necessary to perform
the shearing operation.
The design of the roller must be considered carefully, because it affects the shape of the
component, the wall thickness, and dimensional accuracy. The smaller the tool nose radius, the
higher the stresses and poorest thickness uniformity achieved.
Advantages.
1. Good mechanical properties
2. This process used widely in the production of lightweight items.
3. Very good surface finish.
4. dimensional accuracy.
Applications
Typical components produced by mechanically powered spinning machines include rocket nose
cones, gas turbine engine etc. Being able to achieve almost net shape, thin sectioned parts.
***THANK YOU***

31. UNIT 2.
ADVANCED MANUFACTURING PROCESS
Advanced Welding ,
casting and
forging processes
Semester VII – Mechanical Engineering SPPU
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32. II Shri Swami Samarth II
Unit. 2
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Advanced Welding, Casting and Forging processes
AMP
Unit.2
 Syllabus
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.
Insem-Aug-2015.6M
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
means that the objects are joined without reaching melting point. This opens up whole new areas
1. Friction Stir Welding

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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.
Rotation Speed N
W.P
Thic
kness
Retreating side
Advancing Side

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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.
 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.
 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.
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.

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 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,
(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.
(3) Large Force 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.

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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.
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
2. Introduction to Tooling

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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
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.

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 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.
 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
The type of tooling depends on the type of manufacturing process. Table.1, lists examples
of special tooling used in various operations
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)

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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)
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.
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.
3. Die Casting

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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.
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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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.
4. METAL FLOW IN VACUUM DIE CASTING

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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.
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.
5. METAL FLOW IN SQUEEZE CASTING

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Die-casting is a method that produces a product by pouring melt into a mold followed by
punch-pressing, which allows a complicated shape to be fabricated. However, because die- casting
injects melt at a high velocity, gases and air remaining in the melt may cause internal defects;
therefore, the product’s mechanical properties are degraded. An enhanced die-casting method,
vacuum die-casting, has been developed by adding a vacuum device. Because vacuum die casting
creates a vacuum inside the mold cavity during casting, gases or air in the melt is removed,
decreasing the volume of gas pockets and improving the mechanical properties and smoothness of
the resulting surface. Using an aluminum or magnesium alloy made by vacuum die-casting, aircraft
and automotive parts in bulk shapes have been manufactured. The mold is encapsulated in a
housing that is sealed and placed above the furnace of molten metal. The sprue or gating, or some
form of spout, which is located at the bottom of the mold in the housing, is submerged into the
metal. A vacuum is then applied to the housing, which evacuates the atmosphere in the housing to
create differential pressure between atmosphere pressure above the melt and inside the mold. This
differential pressure is what forces the molten metal from below the surface into the mold cavity.
While gravity pouring has its advantages, within some geometries it can result in a
turbulent metal flow that can lead to entrained gas. The objective of vacuum casting is to control
the metal flow as much as possible for a tranquil mold fill. For metal castings that call for a sound,
consistent integrity, vacuum casting may deliver. The following advantages of vacuum casting
lend the process to precision applications:
6. Vacuum Die
Casting

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1. flow rate of molten metal into the mold cavity can be accurately controlled,
2. improving overall metalcasting soundness;
3. flow rate of the molten metal can be increased to fill the mold cavity more quickly than
with gravity pouring, resulting in the fillout of thinner casting sections; metal drawn into
the mold cavity is from below the surface of the molten metal bath,
4. Avoiding slag and inclusions;
5 . Critical metal temperature variations can be more consistently controlled since the mold is
taken to the furnace rather than vice versa;
6. good surface finish;
7. Excellent dimensional tolerances;
8. It is often easier to automate than gravity pouring.
9. Prolongs die life, eliminates debarring operation and increases up time of casting machine.
Insem-Aug 2015.6M
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.
Squeeze casting as liquid-metal forging, is a process by which molten metal solidifies
under pressure within closed dies positioned between the plates of a hydraulic press. The applied
7. Squeeze casting

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pressure and instant contact of the molten metal with the die surface produce a rapid heat transfer
condition that yields a pore-free fine-grain casting with mechanical properties approaching those
of a wrought product. The squeeze casting process is easily automated to produce near-net to net
shape high-quality components.
The process was introduced in the United States in 1960 and has since gained widespread
acceptance within the nonferrous casting industry. Aluminum, magnesium, and copper alloy
components are readily manufactured using this process. Several ferrous components with
relatively simple geometry for example, nickel hard-crusher wheel inserts-have also been
manufactured by the squeeze casting process.
The squeeze casting process, combining the advantages of the casting and forging
processes, has been widely used to produce quality castings. Because of the high pressure applied
during solidification, porosities caused by both gas and shrinkage can be prevented or eliminated.
The cooling rate of the casting can be increased by applying high pressure during solidification,
since that contact between the casting and the die is improved by pressurization, which results in
the foundation of fine-grained structures.
Macro segregation has been known to be easily founded in most squeeze castings, which
leads to non-uniform macrostructures and mechanical properties. It is generally considered that
pressurization during solidification prevents the foundation of shrinkage defects. However, it
enhances the foundation of macro segregates in squeeze castings of aluminum alloys. Foundation
of macro segregates in castings or ingots has been reported to be caused by interdendritic fluid
flow, which is driven by solidification contraction, differences in density, etc.
Squeeze casting is simple and economical, efficient in its use of raw material, and has
excellent potential for automated operation at high rates of production. The process generates the
highest mechanical properties attainable in a cast product. The microstructural refinement and
integrity of squeeze cast products are desirable for many critical applications.

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As shown in Fig., squeeze casting consists of entering liquid metal into a preheated,
lubricated die and forging the metal while it solidifies. The load is applied shortly after the metal
begins to freeze and is maintained until the entire casting has solidified. Casting ejection and
handling are done in much the same way as in closed die forging. There are a number of variables
that are generally controlled for the soundness and quality of the castings.
 Casting Parameters
Casting temperatures depend on the alloy and the part geometry. The starting point is normally 6
to 55°C above the liquids temperature. Tooling temperatures ranging from 190 to 315°C are
normally used. Time delay is the duration between the actual pouring of the metal and the instant
the punch contacts the molten pool and starts the pressurization of thin webs that are incorporated
into the die cavity. Pressure levels of 50 to 140 MPa are normally used. Pressure duration varying
from 30 to 120s has been found to be satisfactory for castings weighing 9 kg. Lubrication. For
aluminum, magnesium, and copper alloys, a good grade of colloidal graphite spray lubricant has
proved satisfactory when sprayed on the warm dies prior to casting.

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* Advantages
1. Offers a broader range of shapes and components than other manufacturing methods
2. Little or no machining required post casting process
3. Low levels of porosity
4. Good surface texture
5. Fine micro-structures with higher strength components
6. No waste material, 100% utilization
7.No blow hole.
8.Heat treatable
* Limitations
1. Costs are very high due to complex tooling
2. No flexibility as tooling is dedicated to specific components
3. Process needs to be accurately controlled which slows the cycle time down and increases process
costs.
4. High costs mean high production volumes are necessary to justify equipment investment
 Application
Fuel pipe, Scroll, Rack housing, Wheel, Suspension arm, Brake caliper, No Shrinkage porosity, Cross
member node, Engine block, Brake disc, Piston.
********** Thank You ***********

55. UNIT 3.
ADVANCED MANUFACTURING PROCESS
Advanced
techniques for
Material
Processing
Semester VII – Mechanical Engineering SPPU
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56. II Shri Swami Samarth II
Unit.3 AMP
Advanced Techniques For Material Processing
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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57. 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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58. 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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59. 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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60.  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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61. 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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62. 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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63. 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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64. 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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65.  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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66. 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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67. 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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68. 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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69. 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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70. 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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