unit-1.ppt MANUFACTURING TECHNOLOGY METAL JOINING

MANUFATURING TECHNOLOGYT

1. Casting
Unit-1
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2. Casting since about 4000 BC…
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Ancient Greece; bronze
statue casting circa 450BC
Iron works in early Europe,
e.g. cast iron cannons from
England circa 1543

3. Applications
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Transport: Automobile Railways and shipping
Heavy Equipment's: Constrictions Framing and mining.

4. Casting
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5. SandCasting

6. Steps in sand Casting
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7. Casting Process
Cast products
Advantages
•any complex shape can be cast
•any ferrous or non ferrous metals & alloys are castable
•Tools required for casting molds are simple & inexpensive
Limitations
•surface finish and dimensional accuracy is less in sand
casting process

8. Pattern
•It is the replica of the object to be made by
the casting process,with some modifications.
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9. Schematics of Different Patterns

10. Functions of the Pattern
A pattern is used to make a mold cavity.
A pattern may contain projections known as
core prints if the casting needs to be made
hollow.
Runner, gates, and risers used for feeding
molten metal in the mold cavity may be a part of
the pattern.
Proper patterns with good surface finish reduce
casting defects.
A properly constructed pattern minimizes the
overall cost
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11. Pattern Material
A pattern may be made up of wood, plastic, rubber,
wax etc. The imp. Properties which the pattern matl.
must possess are:
•light in weight
•strong, hard and durable
•resistant to wear and corrosion
•dimensionally stable(unaffected by temp.,humidity)
Different types of patterns available
•solid pattern
•split pattern
•match plate pattern
•cope and drag pattern
•sweep pattern
•skeleton pattern

12. Solid or single piece pattern
A single piece pattern is the simplest of all the patterns, is made
in one piece and carries no joint, partition or loose pieces.
Depending upon the shape, it can be moulded in one or two
boxes. The pattern is the cheapest but its use can be done to a
limited extent of production only since its moulding involves a
large number of manual operations like gate cutting, providing
runners and risers.
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13. Two piece or split pattern
•Many times the design of casting offers difficulty in mould
making and withdrawal of pattern, if a solid pattern is used.
For such castings, split or two piece pattern are employed.
They are made in two parts which are joined at the parting
line by means of dowels. While moulding one part of the
pattern is contained by the drag and the other by the cope.
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14. Match plate pattern
These patterns are used where rapid production of small and accurate
castings is desired on a large scale. Their construction cost is quite
high, but the same is easily compensated by a high rate production,
greater dimensional accuracy and minimum requirement for matching
in the casting, these patterns are made in two pieces, one piece is
mounted on one side and the other on the other side of the plate
called match plate. The plate may carry only one pattern, or a group
of patterns mounted in the same way on its two sides. The plate may
be of wood, steel, magnesium or aluminium
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15. Skeletonpatterns
When the size of the casting is very large, but easy to shape and only
a few numbers are to be made, it is uneconomical to make a large
solid pattern of that size. In such cases, a pattern consisting of
wooden frame and strips is made called skeleton pattern. It is filled
with loam sand and rammed. The surplus sand is removed by means
of a stickle. The core can be prepared separately either with the help
of a core box or another skeleton made for that, and assembled in
position in the mould.
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16. Sweep pattern
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Sweeps can be advantageously used for preparing moulds of large symmetrical
castings, particularly of circular cross section. This effect a large saving in time,
labour and material. The full equipment consists of a base, suitably placed in the
sand mass, a vertical spindle and a wooden template called sweep. The outer end
of sweep carries the contour corresponding to the shape of the desired casting. The
sweep is rotated about the spindle to form the cavity. Then the sweep and the
spindle are removed, leaving the base in the sand. The hole made by the removal of
spindle is patched up by filling the sand

17. Pattern with loose-pieces
Some patterns usually single piece, are made to have loose
pieces in order to enable their easy withdrawal from the
mould. These pieces form an integral part of the pattern
during moulding. After the mould it completes, the pattern is
withdrawn leaving the pieces in the sand, which are later
withdrawn separately through the cavity formed by the
pattern.
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18. Cope and drag pattern
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When very large castings are to be made, the complete pattern becomes
too heavy to be handled by a single operator. Such a pattern is made in
two parts which are separately moulded in different moulding boxes. After
completion of the moulds, the two boxes are assembled to form the
complete cavity of which on e part is contained by the drag and other is
cope. Thus, in a way, it is nothing but a two piece or split pattern of which
both the pieces are moulded separately instead of being moulded in the
assembled position.

19. Pattern Material characteristics
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20. Pattern allowances
1.Shrinkage or contraction allowance
2.Draft or taper allowance
3.Machining or finish allowance
4.Distortion or camber allowance
5.Shake allowance

21. Shrinkage or contraction allowance
•Most of the metal have a tendency to contract during
solidification of the metal. The amount of shrinkage
also differs from metal to metal, the factors that
affect the shrinkage are temperature while pouring
the metals, material of the mould specifications of
the casting, method of moulding, casting material.
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22. Shrinkage Allowance
Liquid shrinkage: Refers to the reduction in volume When
liquid metal changes to solid state. Risers are used to
compensate this shrinkage.
Solid shrinkage: Refers to the reduction in volume when solid
metal cools to the ambient temperature to compensate this
reduction shrinkage allowance is given on the patterns
Material Dimension Shrinkage allowance (inch/ft)
Grey Cast Iron
Up to 2 feet
2 feet to 4 feet
over 4 feet
0.125
0.105
0.083
Cast Steel
Up to 2 feet
2 feet to 6 feet
over 6 feet
0.251
0.191
0.155
Aluminum
Up to 4 feet
4 feet to 6 feet
over 6 feet
0.155
0.143
0.125
Magnesium Up to 4 feet
Over 4 feet
0.173
0.155

23. Draft or taper allowance
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Pattern are given slight taper on all vertical surfaces, this taper
is draft allowance. This is either in degrees or linear
measurements and it is provided in internal and external
surfaces. It is provided for easy withdrawal of the pattern. Draft
allowance depends upon its vertical height and moulding
method.

24. Machining or finish allowance
•Machining may be required by the casting, may be
partially or fully. In drawing the portion to be machined
is identified and in those portions machining allowance
is also provided, apart from shrinkage allowance.
Machining allowance also depends upon casting metal,
machining methods, specification of casting and the
finish required.
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25. Aluminum Piston
Aluminum piston for an internal combustion engine.
(a) As cast; (b) after machining.

26. Metal Dimension (inch)Allowance (inch)
Cast iron
Up to 12
12 to 20
20 to 40
0.12
0.20
0.25
Cast steel
Up to 6
6 to 20
20 to 40
0.12
0.25
0.30
Non ferrous
Up to 8
8 to 12
12 to 40
0.09
0.12
0.16
Machining Allowance

27. Distortion or camber allowance
There are certain casting in which the cooling of the metal is not uniform
throughout the casting due to very complicated shape. Due to this there is
distortion in the castings. To minimize its effect distortion in opposite
direction is given in the pattern.
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28. Shake allowance
Before withdrawal of the pattern first of all it is
shaken so that it is free from adjoining walls, due to
this size of mould cavity increases so a negative
allowance is given to pattern.
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29. Rapping Allowance
To facilitate easy withdrawal of the pattern, it is sometimes
rapped all around the vertical faces to slightly enlarge the mold
cavity. Hence the original pattern dimension should be reduced
to compensate for this increase in dimension of the mold
cavity. However it is difficult to quantify this allowance.

30. Molding Materials and their properties
Mold materials include molding sand, backing sand,
Facing sand, core sand etc. The imp. Properties are:
•refractoriness
•permeability
•green strength
•dry strength
•hot strength
•collapsibility
Molding sand composition
•base sand
•binder
•moisture

31. Base Sand
Silica sand is most widely used.Also zircon sand,
chromite sand and olivine sand can be used
Binders
•clay binders
•organic binders
•inorganic binders
Most common clay binders are:
Kaolinite /fire clay (Al
2
O
3
2 SiO
2
2 H
2
O) &
Bentonite (Al
2
O
3
4 SiO
2
nH
2
O)
Bentonite has higher moisture absorbing power
Moisture required for bonding action of the clay

32. Core and Core prints
•Core prints: In a casting if we want to have a
hole then this is done by core. This core is
placed in the mould on the impressions made
in the sand. These projections are core prints.
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33. Core
•A core is a body made of refractory materials
which is set into the prepared mould before
closing and pouring ,for forming the holes,
recesses, projections, undercuts and internal
cavities
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34. Essential Qualities of Core
•Core sand have high refractoriness.
•Good permeability.
•Sufficient Collapsibility.
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Core sand
Silica sand and an organic binder
and very little clay content

35. Core Making Sequence
•Moulding a green core
•Baking and curing
•Finishing
•Coating
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36. Core Making Type
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Conventional
Hot Core Box
Hand M/C
Blowing
m/c
Extrusion

37. Core Types
•Acc to state of core
–Green sand core
–Dry sand core
•Acc to the position of the core in the Mould
–Horizontal core
–Vertical Core
–Balanced Core
–Drop Core
–Hanging Core
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38. Horizontal Core
It is the simplest type of core which is placed
horizontally at the parting line of the mould. As per
cross section, it may be of any shape but cylindrical
shaped core is mostly used.
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39. Vertical Core
•It is similar to horizontal core, only differs in its position.
Vertical core is placed in the mould with its axis vertical.
Normally, top and bottom ends of the core are provided with
a toper .
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40. Balanced Core
•Balanced Core It is suitable to produce a blind hole
along a horizontal axis in casting. The overhanging
length of the core is supported by means of chaplets
as shown in Figure
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41. Hanging or Cover Core
•The core which has no support at the bottom and hangs
vertically from the cope (Figure) is known as hanging core. In
this case, the entire mould cavity is prepared in the drag only.
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42. Chaplets
•These are small metal supports that bridge the gap between
the mold surface and the core, but because of this become
part of the casting. As such, the chaplets must be of the same
or similar material as the metal being cast.
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43. Cheeks
When casting a reentrant angle instead of
using a core a cheekcan be used instead.
This is a third segment in the flask , in
addition to the cope and drag. This allows the
entire mold to be made from green sand and
from removable patterns.
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44. Classification of Casting Processes
Conventional Molding Processes
•Green sand molding
•Dry sand molding
Chemical sand molding processes
•Shell Molding
•Sodium silicate Molding
Permanent Mold Processes
•Gravity die casting
•Pressure die casting
Special Casting Processes
Investment Casting
Centrifugal casting

45. Shell Molding Process
3 to 8% phenolformaldehyde / ureaformaldehyde thermosetting resin
Lubricants like zinc/calcium stearate improve flowability
230 to 350
o
C

46. Green Sand Mold making procedure
Dry facing sand sprinkled
on board & pattern & then
Molding sand is packed
Cope half placed over the
Drag half Parting sand
Sprinkled over the drag
& the pattern Sprue pin,
Riser pin placed
Facing sand in the form
of paste applied in the
Mold cavity The mold
is now ready for pouring

47. Dry Sand molds
To lower gas forming materials in the mold sometimes
Air dried molds are used.
Drying of molds can be of two types:
•skin dried
•complete mold drying
Common methods of drying the mold
•hot air
•gas or oil flame
Skin drying accomplished with the aid of torches
Directed at the mold surface

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Pattern creation-A two-piece metal pattern is created in the
shape of the desired part, typically from iron or steel. Other
materials are sometimes used, such as aluminum for low volume
production or graphite for casting reactive materials.
Mold creation-First, each pattern half is heated to 175-370°C
and coated with a lubricant to facilitate removal. Next, the
heated pattern is clamped to a dump box, which contains a
mixture of sand and a resin binder. The dump box is inverted,
allowing this sand-resin mixture to coat the pattern. The heated
pattern partially cures the mixture, which now forms a shell
around the pattern. Each pattern half and surrounding shell is
cured to completion in an oven and then the shell is ejected
from the pattern.
Shell mold casting process

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Mold assembly-The two shell halves are joined together and
securely clamped to form the complete shell mold. If any
cores are required, they are inserted prior to closing the
mold. The shell mold is then placed into a flask and
supported by a backing material.
Pouring-The mold is securely clamped together while the
molten metal is poured from a ladle into the gating system
and fills the mold cavity.
Cooling -After the mold has been filled, the molten metal is
allowed to cool and solidify into the shape of the final casting.
Casting removal -After the molten metal has cooled, the
mold can be broken and the casting removed. Trimming and
cleaning processes are required to remove any excess metal
from the feed system and any sand from the mold.

51. Advantages of Shell Mould Casting
•Good surface finish
•High dimensional tolerance
•Amenable towards automation
•Castings weighing up to 450 kg’s can be cast by this process.
•Thin sections (up to 0.25 mm) can be cast by this process
Limitations
•Patterns are expensive.
•Castings weighing more than 450 kg’s cannot be made.
•Highly complicated shapes cannot be made.
Applications
•Cast iron, Aluminum and copper alloys are cast by this process

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Investment casting

53. Steps followed in Investment Casting Process
1.A heat disposable pattern made of wax or plastic is made
2.A pattern assembly (tree / cluster) is prepared attached to a
central wax sprue
3. Pattern assembly is invested into a ceramic slurry composed of
silica flour suspended in soln. of ethylsilicate. Ceramic shell of
6mm thickness is formed around the wax assembly.
4. The assembly baked in oven to melt out the wax/plastic thereby the
dimensions of mold cavity precisely match those of the product
5. The shell mold is fired at 900 to 1000
0
C to remove all traces of wax
and also the strength gets enhanced
6. Molten metal is poured when the mold is still hot resulting in a
production of a cluster of castings at a time

54. Applications of Investment Casting
•Intricate shaped objects like jewelry
•Cylinder heads
•cam shafts
•gas turbine blades
Advantages of Investment Casting Process
•Complicated and intricate shaped products can be easily cast
•High dimensional tolerance achievable
•Surface finish is excellent
•Additional machining not required as it is a net shape process
•All types of metals and alloys can be cast by this process
Limitations
•A relatively expensive process
•Size of the casting is limited (max. around 5 kg)

55. Permanent Mold Materials:
•Fine grained grey cast iron
•Alloy steels for large volumes and large parts
•Graphite for small volume castings of Al & Mg
The die life depends on
The melting temperature of metals and alloys
Materials normally cast in permanent molds
•Al. alloys
•Mg alloys
•Zn alloys
•Grey Cast Iron
Permanent Mold casting / Gravity Die casting
The molds are coated with refractory to a layer of 8 mm

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69. Die closed and plunger withdrawn
Metal forced
into die cavity at
fixed press.
Plunger
withdrawn
& die opened
Press. 50 to
150 atm
Hot Chamber Die Casting

70. Advantages of Hot Chamber Die Casting
•Improved productivity
•Superior surface finish
•High tolerance
•Intricate shapes with thin walls can be easily produced
Limitations
•Only low melting alloys (such as Zn, Sn, Pb) are cast
•Small castings weighing less than 4.5 kg can be cast

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74. Vertical Type

75. Horizontal Type

76. Cold chamber die casting suitable for casting of
•Aluminium alloy
•Mg alloys
•Brass etc
Pressure applied in cold chamber die casting method can be
as high as 2000 atmospheres
Advantages
•high temperature metals and alloys can be cast
•large parts (weighing around 25 kgs) can be cast
•high surface finish ( 1 m) and dimensional tolerance
•better mechanical properties of the casting because of the fine grains
Limitations
•large cycle time
•metal sometimes looses the superheat and cause defects such as
“cold shut”
•dies and the machines are expensive

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Gravity Die Casting
Gravity die casting is a process wherein the liquid metal is
poured into metallic moulds without application of any
external pressure. The liquid metal enters the cavity by
gravity

79. Advantages of Gravity Die Casting
•A fine grained casting with superior mechanical properties
•Good surface finish (4 microns)
•Good dimensional tolerance
•Mass production of castings possible
Limitations
•Maximum weight of casting limited to 15 kgs
•Complicated shapes cannot be produced
Applications
Automobile pistons, stators, gear blanks, connecting rods etc

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Process:
The Mold for Co
2Casting is made of a mixture of
sand and liquid silicate binder which is hardened by passing
Co2 gas over the mold. The equipment of the molding
process include Co
2cylinder, regulator, hoses and hand held
applicator gun or nozzle.
Co
2Moulding process
Sodium silicate + Co2 = Sodium Carbonate + Silica gel

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Applications:
Co2 casting process is ideal where speed and flexibility is the prime
requirement.
molds and cores of a varied sizes and shapes can be molded by this
process.
Advantages:
•Compared to other casting methods cores and molds are strong.
•Reduces fuel cost since gas is used instead of to other costly heating generating
elements .
•Reduces large requirement for number of mold boxes and core dryers.
•Provides great dimensional tolerance and accuracy in production.
•Moisture is completely eliminated from the molding sand.
•This process can be fully automated.

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Continuous casting Process

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Continuous casting Process

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