MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

CASTING PROCESSES SAND MOULD CASTINNG

 In these processes sand aggregates are

 Casting is a manufacturing process in
used to make the moulds.
which a liquid material is usually
poured into a mold, which contains a  The molten metal is poured in to sand

hollow cavity of the desired shape, and mould and allowed to solidify the

then allowed to solidify. product may be called as "sand

casting"
 The solidified part is also known as
a casting, which is ejected or broken PERMANENT MOULD CASTING (GRAVITY
out of the mold to complete the DIE CASTING)
process.
 A casting produced by pouring molten
TYPES OF CASTING PROCESSES metal in a metallic mould is known as

(1) Sand mould casting permanent mould casting.

 Metallic moulds are called dies.
(2) Permanent mould casting
 Pouring in permanent moulds is done
(3) Special casting processes simply due to gravity. (Without any
external pressure) and hence it
(a) Die casting
generally is also called as gravity die
(i) Hot chamber process casting.

(ii) Cold chamber process  Permanent moulds are made non-

ferrous of cast iron and alloy steel.
(b) Slush casting

(c) Centrifugal casting

(d) Plaster mould casting

(e) Shell mould casting

(f) Investment casting. Etc

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

Pressure die casting  When the plunger is in up position, the

molten metal enters the cylinder
 In this process, the molten metal is
through a port.
forced into the mould cavity under high
 As the plunger moves down, the port
pressure.
gets closed and the molten metal is
 The process is used for casting
forced in to the die cavity under a
Aluminium, zinc alloys.
pressure.
There are two types of die casting  When the metal has solidified, die is
machines, opened and the casting is ejected.

A. Hot Chamber die casting machines

1. Submerged plunger type or Goose neck

type
2. Direct injection type or Air injection
type

B. Cold chamber die casting machine

Direct injection type or Air injection type
C. Vacuum die casting machines
hot chamber die casting machine
Goose neck type (Submerged plunger
 In this type of die casting machine the
type) hot chamber die casting machine
molten metal from the container is
 In this the melting furnace is an integral forced in to the die by direct air
part of the mould. pressure (30 to 45 bar) acting on the
 This is operated by a pneumatically molten metal.
operated plunger.  In the beginning of the cycle, the goose
 The plunger acts inside a cylinder neck container is sub-merged in the
connected to one end of the goose molten metal and is filled by gravity.
neck container and is submerged in the  Compressed air then forces the metal
molten metal. in to the die and pressure is maintained
till solidification.

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

 When solidification is complete, the

goose neck is lowered down and
 Casting is removed by ejector pins after
opening the dies.

Vacuum die casting machine

 It is a modified form of hot chamber or

cold chamber die casting machine with
a provision for complete evacuation of
air from die.

Cold chamber die casting machine

 In this the melting furnace is not the

integral part of the machine.
 The metal is melted in separate
furnace and brought to this
machine.
 Molten metal is poured to the
chamber and plunger rod is pressed,
Advantages
hence the metal is forced to the
mould cavity. (1) Production rate is high up to 700

 This mould is preheated and a oil castings per hour.

coating is given inside the cavity. (2) Better surface smoothness and surface
 Then molten metal is poured to the details.
cavity.
(3) Close dimensional tolerances can be
 After solidification the metal is
obtained.
taken out by removing clamps.

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

(4) Longer life of dies (eg: life of a die for  The metal is retained in the mould for
zinc-base casting. is up to one million long enough for the outer skin to
castings). solidify.
 Finally thin-walled casting which is
(5) Thin sections can be cast easily.
taken out the metal still liquid.
(6) A number of non-ferrous alloys can be
 The thickness of the mould is upon
die cast.
depends the time for which the metal
(7) Each casting is exact duplicate of the is allowed to remain in the mould.
original.  This method is used for making toys,
ornaments, etc.
Disadvantages

(1) The die casting units are costly.

(2) All metals and alloys cannot be die

cast.

(3) Not economical for small runs.

(4) Special skill is needed for maintenance CENTRIFUGAL CASTING

and operation of die casting machines.

(5) There are limitations in size of castings

to be made.

SLUSH CASTING

 Slush casting is a process used for

making hollow castings without the use
of cores.  Centrifugal casting is a process in which
 In this process, the molten metal is molten metal is poured and allowed to
poured in to a metallic mould solidify while the mould is kept
(permanent mould). revolving.
 The mould is made of metal and lined
with refractory material.
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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

 The mould is rotated at a very high 1. Shift or Mismatch

speed and the molten metal is poured
 The defect caused due to misalignment
in to the cavity by a ladle.
of upper and lower part of the casting.
 The centrifugal force directs the fluid
metal to the inner surface of the mould
with considerable pressure; where
solidification occurs forming hollow
castings.

Advantages Cause

 It is quick and economical than other  Improper alignment of upper and

methods. lower part during mould preparation.
 It eliminates the use of gates, risers,  Misalignment of flask
cores, etc.
Remedies
 The ferrous and non-ferrous metals can
be cast by this process  Proper alignment of the pattern or die

 It produces castings free from part, moulding boxes.

shrinkage  Correct mountings of pattern on

pattern plates.
Applications
 Check the alignment of flask.
 Employed tor casting articles of
2. Swell
symmetrical shape eg: Cast iron pipes.
 Gears fly wheels, hydraulic cylinders,  It is the enlargement of the mold cavity

piston rings, brake drums, etc. because of the molten metal pressure.

CASTING DEFECTS

 It is an unwanted irregularity that

appears in the casting during metal
casting process.

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

Causes  Adequate venting facility should be

provided.
 Defective or improper ramming of the
mould. 4. Drop

Remedies  Drop defect occurs when there is

cracking on the upper surface of the
 The sand should be rammed properly
sand and sand pieces fall into the
and evenly.
molten metal.
3. Blowholes

 When gases entrapped on the surface

of the casting due to solidifying metal,
a rounded or oval cavity is formed
called as blowholes.
Causes

 Soft ramming and low strength of sand.

 Insufficient reinforcement of sand
projections in the cope.

Remedies

Causes  Sand of high strength should be used

with proper ramming.
 Excessive moisture in the sand.
 Sufficient reinforcement of the sand
 Low Permeability of the sand.
projections in the cope.
 Too hard rammed sand.
 Insufficient venting is provided. 5. Metal Penetration

Remedies

 The moisture content in the sand must

be controlled and kept at desired level.
 High permeability sand should be used.
 Sufficient ramming should be done.
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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

 These casting defects appear as an 7. Shrinkage Cavity

uneven and rough surface of the
 The formation of cavity in the casting
casting.
due to volumetric contraction is called
Causes as shrinkage cavity.

 It is caused due to low strength, large

grain size, high permeability and soft
ramming of sand.

Remedies

 This defect can be eliminated by using Causes

high strength, small grain size, low  Uneven or uncontrolled solidification

permeability and soft ramming of sand. of molten metal.

6. Pinholes  Pouring temperature is too high.

 They are very small holes of about 2 Remedies

mm in size which appears on the  This defect can be removed by applying

surface of the casting. principle of directional solidification in

Causes mould design.

 Wise use of chills
 Use of high moisture content sand.
 Absorption of hydrogen or carbon 8. Cold Shut

monoxide gas by molten metal.  When the molten metal enters into the

Remedies mould from two gates and when these

two streams of molten metal meet at a
 By reducing the moisture content of
junction with low temperatures than
the moulding sand.
they do not fuse with each other and
 Increasing permeability of the sand.
solidifies creating a cold shut (appear
 By doing rapid rate of solidification.
as line on the casting). It looks like a
crack with round edge.

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

 The temperature at which

recrystallization takes place, new
grains are formed is called
recrystallization temperature.
COLD WORKING PROCESS
Causes
 When the metal forming process done
 Poor gating system
below its recrystallization temperature,
 Low melting temperature
it is known as cold working process.
 Lack of fluidity
Advantages
Remedies  It gives better dimensional accuracy
compare to hot working.
 Improved gating system.
 No energy source required for heating.
 Proper pouring temperature.
 Cold worked work piece can be
handling easily.

MECHANICAL WORKING OF Disadvantages

 The amount of deformation is limited
METALS
according to the press size.
 Mechanical working is a process of  These metal forming processes require
shaping of metals by plastic higher force to deform the work piece.
deformation.  Brittle work pieces cannot work by cold
1. Cold working working.
2. Hot working.  Higher risk of cracks in cold working.
 During plastic deformation of a metal  It accomplish by internal and residual
the existing grains or crystals are stresses.
distorted or broken out. COLD WORKING OPERATIONS
 The refining of metal is done by
 The various widely used cold working
heating the metal leading to the
operations are
formation of new gains. This is called
1. Drawing
recrystallization.
2. Bending

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

3. Squeezing 2. Tube drawing

4. Shearing  The tube is pulled through the die over
5. Extrusion a fixed mandrel.
6. Shot peening  The Outside diameter of the tube is
7. Hobbing controlled by the opening of the die
DRAWING and the inside bore (diameter) by the
mandrel
 It is the process of producing various
cross- sections by forcing of metal
through a die by means of a tensile
force.

Some of the drawing operations used is

1. Wire drawing
3. Deep drawing
2. Tube drawing
 This process involves the production of
3. Deep drawing
a dish or cup from a flat sheet metal.
4. Metal spinning

5. Stretch forming

1. Wire drawing
 The process of reducing the coss-
section of wire by pulling the wire
through a single or series of dies. 4. Metal spinning (Cold spinning)

 It is an operation of shaping sheet

metal by pressing against a form while
it is rotating.

 The operation is performed on a speed

lathe.

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

 A rotary type, roll bending machine is

employed for bending metal plates and
strips into cylindrical shapes.

5. Stretch forming
 This process consists of gripping a
sheet Metal at each end in suitable
jaws, and stretching it over a die made
to the required contour until complete
forming is achieved.

SQUEEZING

 In squeezing, the metal is made to flow

within the cavity of dies and punch, to
BENDING attain the desired shape.

 This process is also known as forming.  Some of the important squeezing are
1. Cold rolling
 The bars, rods, Ram structural shapes
2. Upsetting
and sheet metals may be bent through
3. Coining
dies.
4. Cold heading.
 In ram type machine two pressure dies 5. Hobbing
are mounted in fixed position on the
Coining
frame of the machine and are free to
rotate about their mounting pins.  Coins, medals and other similar articles
are produced by this process.
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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

 This operation is carried out in dies in

which the metal is confined and
restricted its flow in the lateral
direction.

 Some of the shearing operations are

1. Trimming
2. Blanking and punching etc.

Punching (Piercing):
Embossing
 It is an operation of cutting holes in a
 In this process sheet metal is stretched
sheet metal using punch and die.
to shape under pressure by means of a
 The metal punched out goes as waste
Punch and die.
and the sheet with hole is the required
 A large number of Blank ornamental product.
wares, such as plates in sheet metal are
Blanking
produced by embossing
 The metal punched out is the desired
product and the sheet with the hole
left on the dies goes as waste.

SHEARING

 This is a process of cutting the metal

using the punch and die. The metal to
be cut is placed between the punch
and die.

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

COLD EXTRUSION  Energy required to change the shape is

less compared to cold working
 In this process of extrusion the working
material is placed in to a blind hole of  It is a rapid and economical process.
the die and a punch with clearance is
Disadvantages
forced in to the die which causes the
metal to flow plastically around the  Close tolerances cannot be maintained.

punch.  Tooling and handling cost is high.

 The application of the process are  Rapid oxidation or scale formation

limited to soft and ductile materials takes place on surface, leading to poor
such as lead, tin,aluminum, zinc and surface finish.
some of their alloys.
 Tool life is reduced as the tools have to
work at high temperatures

HOTWORKING PROCESSES

 Hot rolling

 Hot piercing
HOT WORKING OF METALS
 Hot drawing
 Mechanical working of metals above
 Hot spinning
recrystallization temperature is termed
as hot working.  Hot extrusion

Advantages  Forging.

 Porosity of the metal is mostly HOT ROLLING

eliminated  The process of rolling consists of

 Physical properties are improved due passing the hot billets through two

to refinement of grains. feed rolls rotating in opposite

directions at a uniform speed.

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

 The second stage involves repeated

heating and drawing of this cup.

HOT PIERCING
HOT EXTRUSION
 It is the process to produce seamless
tubes.  It is the process of pushing a heated
billet of metal through an orifice
 In this process cylindrical billets are
provided in to the die, thus forming an
passed between two conical shaped
elongated part of uniform cross-
rolls rotating in the same direction.
section.

 Zinc, lead aluminium, copper,

magnesium, nickel and their alloys are
used for extrusion.

Methods of Extrusion

The extrusion processes can be classified

HOT DRAWING
as
 It is mostly used for the production of
1. Direct or forward extrusion
thick- walled seamless tubes and
2. Indirect or backward extrusion
cylinders.
3. Tube extrusion
 The process consists of two stages.
1. Direct or forward extrusion
 The first stage consists of drawing a
 The heated billet is pushed by the press
cup out of a hot circular plate with the
by operating a ram in the cylinder
help of a die and punch

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

(container) through a small restricted HOT SPINNING

opening of the die.
 Hot spinning is the processes of
shaping sheet metal by pressing against
a form, while it is rotating.

 Metals like aluminium, copper, brass

and mild steel are suitable for hot
spinning.

2. Indirect or backward extrusion

 It is similar to forward extrusion with
the difference that the extruded metal
is forced through the hollow ram.

POWDER METALLURGY

 Powder metallurgy is the process by

3. Tube extrusion
which fine powdered materials are

 Used to produce tube sections blended, pressed in to the desired

shape, and then heated in a controlled
 The metal flows through the opening
atmosphere to attain strength and
between the die and the mandrel by
other properties.
applying a pressure in the ram.
Basic steps in powder metallurgy process

1) Powder manufacture

2) Mixing and blending

3) Compacting

4) Sintering

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

1) Powder manufacture sufficiently high temperature and

pressure to cause the loose to become
 Some of the common methods are
a compact solid piece.
atomization, crushing and milling,
 The purpose of sintering is to impart
machining, electrolytic deposition,
strength and integrity to the material.
shotting, granulation. etc.
Applications (products) of powder
2) Mixing and Blending
metallurgy
 The mixing and blending is used to
 High precision parts of aircrafts, gas
obtain homogeneous mixture of
turbines, cams, sewing machines. etc.
alloyed powders with uniform
 Filaments of bulbs, x-ray tubes, radio
distribution of particle sizes.
valves. etc.
 The majority of powders are mixed
 Hard carbide alloys for dies and cutting
with binders & lubricants to achieve
tools.
the desired characteristics in the
 Production of electric resistance
finished product.
welding electrodes.
 Blending means the thorough
 Anti-friction alloys, antifriction
intermixing of powders of different
bearings.
grain sizes of the same composition.
 Bimetalic strips and laminated special
Compacting (Briquetting)
purpose parts can be made from mould

 It is an operation of compacting loose layers of different metal powders.

metal powder in moulds by the  Mechanically alloyed super alloys.

application of pressure and densified  Production of 'Cermets' (ceramics +
into a shape, known as green compact metals) - The material is mainly used as
or green briquette. a tool material.

Sintering Advantages of Powder metallurgy

 Sintering is a heat treatment process in  Elimination or reduction of machining.

which a large quantity of loose  Close dimensional tolerances.
aggregate material is subjected to a

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MANUFACTURING TECHNOLOGY M2 PRAVEEN KP Lr: in ME

 Mixture of metallic and non-metallic

materials to get special properties.
 High production rate by automation
process.
 No waste of materials.
 Production of complex shapes.
 High skilled labour not required.

Disadvantages/Limitations

 Dies and equipment costs are high.

 Expensive products due to expensive
powders.
 Lower strength of finished
components.
 High porosity and tendency to
oxidation.
 Low impact strength and fatigue
strength.
 Limited shapes due to die design
problems.

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