Manufacturing Technology

MANUFACTURING TECHNOLOGY
MME 2152: MANUFACTURING TECHNOLOGY [4 0 0 4]

Foundry: Moulding, Types of moulding, Moulding materials, Moulding sand,

MANUFACTURING TECHNOLOGY
Composition of moulding sand. Sand Testing - Permeability test, Strength test,
Moisture content test, Clay content test, Grain fineness test. [05]

Casting: Types of casting- Investment casting, Permanent mould casting, Slush

casting, Pressure die casting (Hot chamber & Cold chamber), Centrifugal casting
and Continuous casting, Advantages & limitations of casting process. [05]

Welding: Classification of welding processes, Metal arc welding, Consumable

and non-consumable arc welding process, Submerged arc welding, TIG, MIG,
Electro-slag, Resistance welding - Spot, Seam, Projection. Special type of welding
- Thermit welding, Friction welding, Advantages, limitations and applications of
welding. [05]

Mechanical working of metals: Cold, Warm, Hot working. Sheet metal forming-
Shearing, Shearing operations – Punching, Blanking, Embossing, Coining,
Lancing, Slitting, Bending, Bulging, Curling and Roll forming, Extrusion and
Drawing Processes. [04]

Theory of metal cutting: Orthogonal and Oblique cutting, Cutting parameters -

speed, feed, depth of cut and their selection criteria; Machinability parameters,
Tool life and wear. Merchant’s analysis, Taylor’s equation and factors affecting
tool life. Numericals on shear plane angle, Cutting force and tool life calculation.
[05]
Machine Tools: Lathe - Constructional features, accessories and attachments,
back gear arrangement, lathe operations and calculations of machining time.
Drilling - Constructional features of radial drilling machine, twist drill
nomenclature and computation of drilling time.
Milling - Constructional features of column and knee type milling machine,
attachments, milling operations, types of milling cutters, Indexing: direct, simple
and compound indexing and machining time calculations. [12]

Grinding: Grinding wheel – Abrasive particles, Bonding materials, Designation

and selection, Dressing and truing. Constructional features and principles of
cylindrical, surface and centreless grinding machines. Finishing Operations –
Lapping, Honing and Buffing. [03]

Non-conventional machining: Principles, Working, Equipment, Advantages,

Limitations, Applications of Abrasive Water Jet Machining (AWJM), Ultrasonic
Machining (USM), Electrical Discharge Machining (EDM), Laser Beam
Machining (LBM), Electron Beam Machining (EBM). [05]

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Processing of plastics and Rapid prototyping: Extrusion, Injection moulding, Blow

moulding, Rotational moulding, Thermoforming, Compression moulding, Transfer
moulding, Rapid prototyping - Working principle, advantages, limitations & applications
of fused deposition modeling, stereo lithography and selective laser sintering. [04]

References:
1. Rajput R. K., A Text book of Manufacturing Technology, Laxmi Publications Private
Limited, 2011.
2. Khanna O.P., A text book of Production Technology, Dhanpat Rai Publications,
2011.
3. Rao P. N., Manufacturing Technology, Tata McGraw-Hill Publishing Company
Limited, New Delhi, 2006.
4. Serope Kalpakejian and Steven Schmid R, Manufacturing Engineering and
Technology, Pearson Education, Delhi, 2005.
5. Paul DeGarmo E., Black J. T. and Ronald Kohser A, Materials and Process in
Manufacturing, John Wiley and Sons, Delhi, 2004.
6. Lal M. and Khanna O. P., Foundry Technology, Dhanpat Rai and Sons, New Delhi,
1991.
7. Benedict G. F., Non Traditional Machining Techniques, Marcel Decker, New York,
1990.
8. Weller E. J., Non-Traditional Machining, Society of Manufacturing Engineers,
Dearborn, 1984.
9. Degarmo Paul, Materials and Processes in Manufacturing, Macmillan Publishing
Company Inc., New York, 1986.
10. Jain R. K., Production Technology, Khanna Publishers, Delhi, 2001.
11. Chua C K, Leong K F and Lim C S, Rapid Prototyping: Principles and Applications,
World Scientific, Singapore, 2003.

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1. Foundry
Introduction:
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting
them into a liquid, pouring the metal in a mold, and removing the mold material or casting
after the metal has solidified as it cools. The most common metals processed are aluminium
and cast iron. However, other metals, such as bronze, brass, steel, magnesium, and zinc, are
also used to produce castings in foundries. In this process, parts of desired shapes and sizes
can be formed.

Moulding:
Sand casting, also known as sand molded casting, is a metal casting process characterized by
using sand as the mold material. It is relatively cheap and sufficiently refractory even for steel
foundry use. A suitable bonding agent (usually clay) is mixed or occurs with the sand. The
mixture is moistened with water to develop strength and plasticity of the clay and to make
the aggregate suitable for molding. The term "sand casting" can also refer to a casting
produced via the sand casting process. Sand castings are produced in specialized factories
called foundries.

Molding is the operation necessary to prepare a mold for receiving the metal. It consists of
ramming sand around the pattern placed in support, or flask, removing the pattern, setting
cores in place, and creating the gating/feeding system to direct the metal into the mold cavity
created by the pattern, either by cutting it into the mold by hand or by including it on the
pattern, which is most commonly used.
Types of Patterns:
1. Single-piece pattern
These are inexpensive and the simplest type of patterns. As the name indicates, they are
made of a single piece. This type of pattern is used only in cases where the job is simple and
does not create any withdrawal problems. This pattern is expected only to be in the drag and
should have a flat surface which serves as the parting plane. If no flat surface exists then a
follow board needs to be used.

Figure 1: Single piece Pattern

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2. Split pattern or Two-piece pattern

This is the most widely used type of pattern for intricate castings. The split surface of the
patterns serves as the plane for parting. The two halves should be aligned properly by making
use of dowel pins which are found on the cope half of the pattern.

Figure 2: Split piece pattern

3. Gated pattern
This is an important improvement over the simple pattern where the gating and runner
system are integral with the pattern. This eliminates hand cutting of runners and gates
thereby improving the productivity.

Figure 3: Gated pattern

4. Cope and Drag pattern

These are similar to split pattern. These come attached to metal or wooden plates along with
alignment pins. These are used as patterns in castings which are heavy and inconvenient to
handle. Some of the cope and drag pattern may come with a gating and runner system
integral with it.

Figure 4: Cope and Drag pattern

5. Match plate pattern
These are extensions of the cope and drag patterns. Here are the cope and drag patterns are
mounted on a single matching plate. On one side of the plate cope flask is prepared while
drag flask is prepared on the opposite face. Match plate pattern may have a gating and runner
system as an integral part of the plate. Plate is usually made of aluminum or steel.
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Figure 5: Match plate pattern

6. Loose piece pattern
This type of pattern is used when the contour of the part is such that, withdrawing the pattern
from the mould is not possible. Hence, during moulding, the obstructing part of the contour
is held as a loose piece. After moulding is over, the main pattern is first removed and then the
loose pieces are recovered through the gap generated by the main pattern.

Figure 6: Loose piece pattern

7. Follow board pattern
This type of pattern is adopted for those castings where there are some portions, which are
structurally weak and if not supported properly are likely to break under the forces of
ramming. Hence the bottom board is modified as a follow board to closely fit the contour of
the weak pattern and thus supports it during the ramming. It may also be used to support a
pattern not having a flat surface. In such cases, a seat is formed on the follow board which
supports the pattern in it during flask preparation.

Figure 7: Follow board pattern

8. Sweep pattern

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It is used to sweep the complete casting by means of a plane sweep. These are used for
generating large shapes which are axi-symmetric or prismatic in nature such as bell shaped or
cylindrical.

Figure 8: Sweep pattern

9. Skeleton pattern.
A skeleton of the pattern made of strips of wood is used for building the final pattern by
packing sand around the skeleton. After packing the sand, the desired form is obtained with
the help of a strickle. This type of pattern is useful generally for very large castings, required
in small quantities having simple shape, where large expense on the complete wooden
pattern is not justified.

Figure 9: Skeleton pattern

10. Segmental pattern
A segmental pattern resembles a sweep pattern in the sense that for getting the required
shape both employ a part or a portion of the pattern and not the full or complete pattern.
Both of these generate circular shapes. The difference is that segmental patterns do not
revolve continuously about the post to make the mould, rather it prepares the mould by parts.

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Figure 10: Segmental pattern

Types of Moulding:
Molding processes can be classified in a number of ways. Broadly they are classified either on
the basis of the method used or on the basis of the mold material used.
(i) Classification based on the mold material used:
(a) Sand molding:
1. Green sand mold
2. Dry sand mold,
3. Cement bonded sand mold
4. Carbon-dioxide mold.
5. Shell mold.
(b) Plaster molding,
(c) Metallic molding.
(ii) Classification based on the method used
(a) Bench molding. (b) Floor molding,
(c) Pit molding. (d) Machine molding.

Molding Material and Properties

A suitable and workable material possessing high refractoriness in nature can be used for
mold making. Thus, the mold making material can be metallic or non-metallic. For metallic
category, the common materials are cast iron, mild steel and alloy steels.In the non-metallic
group molding sands, plaster of paris, graphite, silicon carbide and ceramics are included. But,
out of all, the molding sand is the most common utilized non-metallic molding material
because of its certain inherent properties namely refractoriness, chemical and thermal
stability at higher temperature, high permeability and workability along with good strength.
Moreover, it is also highly cheap and easily available. A large variety of molding materials is
used in foundries for manufacturing molds and cores. They include molding sand, system sand
or backing sand, facing sand, parting sand, and core sand.

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Types of Molding Sand:

Depending upon the purity and other constituents present, sand is classified into
(i) Natural sand. (ii) Synthetic sand, (iii) loam sand.

(i) Natural sand:

Natural sand is directly used for molding and contains 5-20% of clay as binding material. It
needs 5-8% water for mixing before making the mold. Many natural sands possess a wide
working range of moisture and are capable of retaining moisture content for a long time. Its
main drawback is that it is less refractory as compared to synthetic sand. Many natural sands
have weak molding properties. These sands are reconditioned by mixing small amounts of
binding materials like bentonite to improve their properties and are known as semi-synthetic
sand.

(II) Synthetic Sands:

Synthetic sand consists of silica sand with or without clay, binder or moisture. It is a
formulated sand i.e. sand formed by adding different ingredients. Sand formulations are done
to get certain desired properties not possessed by natural sand. These sands have better
casting properties like permeability and refractoriness and are suitable for casting ferrous and
non-ferrous materials. These properties can be controlled by mixing different ingredients.
Synthetic sands are used for making heavy castings.

(III) Loam Sand:

Loam sand contains many ingredients, like fine sand particles, finely ground refractories, clay,
graphite and fiber reinforcements. In many cases, the clay content may be of the order of 50%
or more. When mixed with water, the materials mix to a consistency resembling mortar and
become hard after drying. Big molds for casting are made of brick framework lined with loam
sand and dried. Sweeps etc. are used for making big castings like big bells by using loam sand.

Constituents of Molding Sand:

The main constituents of molding sand involve silica sand, binder, moisture content and
additives.

Silica sand
Silica sand in form of granular quarts is the main constituent of molding sand having enough
refractoriness which can impart strength, stability and permeability to molding and core sand.
Along with silica small amounts of iron oxide, alumina, lime stone, magnesia, soda and potash
are present as impurities. The chemical composition of silica sand gives an idea of the
impurities like lime, magnesia, alkalis etc. present. The presence of excessive amounts of iron
oxide, alkali oxides and lime can lower the fusion point to a considerable extent which is
undesirable.

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Moisture
The amount of moisture content in the molding sand varies generally between 2 to 8 percent.
This amount is added to the mixture of clay and silica sand for developing bonds. This is the
amount of water required to fill the pores between the particles of clay without separating
them. This amount of water is held rigidly by the clay and is mainly responsible for developing
the strength in the sand. The effect of clay and water decreases permeability with increasing
clay and moisture content. The green compressive strength first increases with the increase
in clay content, but after a certain value, it starts decreasing.

Additives
Additives are the materials generally added to the molding and core sand mixture to develop
some special property in the sand. Some common used additives for enhancing the properties
of molding and core sands are.

(i) Coal dust

Coal dust is added mainly for producing a reducing atmosphere during casting. This reducing
atmosphere results in any oxygen in the poles becoming chemically bound so that it cannot
oxidize the metal.

(ii) Dextrin
Dextrin belongs to starch family of carbohydrates. It increases dry strength of the molds.

(iii) Pitch
It is distilled form of soft coal. It can be added from 0.02 % to 2% in mold and core sand.
It enhances hot strengths, surface finish on mold surfaces.

(iv) Wood flour

This is a fibrous material mixed with a granular material like sand; its relatively long thin fibers
prevent the sand grains from making contact with one another. It can be added from 0.05 %
to 2% in mold and core sand. It increases collapsibility of both of mold and core.

The choice of molding materials is based on their processing properties. The properties that
are generally required in molding materials are:

Refractoriness
It is the ability of the molding material to resist the temperature of the liquid metal to be
poured so that it does not get fused with the metal. The refractoriness of the silica sand is
highest.

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Permeability
During pouring and subsequent solidification of a casting, a large amount of gases and steam
is generated. These gases are those that have been absorbed by the metal during melting, air
absorbed from the atmosphere and the steam generated by the molding and core sand. If
these gases are not allowed to escape from the mold, they would be entrapped inside the
casting and cause casting defects. To overcome this problem the molding material must be
porous. Proper venting of the mold also helps in escaping the gases that are generated inside
the mold cavity.

Green Strength
The molding sand that contains moisture is termed as green sand. The green sand particles
must have the ability to cling to each other to impart sufficient strength to the mold. The
green sand must have enough strength so that the constructed mold retains its shape.

Dry Strength
When the molten metal is poured in the mold, the sand around the mold cavity is quickly
converted into dry sand as the moisture in the sand evaporates due to the heat of the molten
metal. At this stage the molding sand must possess the sufficient strength to retain the exact
shape of the mold cavity and at the same time it must be able to withstand the metallostatic
pressure of the liquid material.

Hot Strength
As soon as the moisture is eliminated, the sand would reach at a high temperature when the
metal in the mold is still in liquid state. The strength of the sand that is required to hold the
shape of the cavity is called hot strength.

Collapsibility
The molding sand should also have collapsibility so that during the contraction of the solidified
casting it does not provide any resistance, which may result in cracks in the castings. Besides
these specific properties the molding material should be cheap, reusable and should have
good thermal conductivity.

Test on Moulding Sands:

➢ Moisture content test
➢ Clay content test
➢ Grain fineness test
➢ Permeability test
➢ Strength test

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Moisture content test:

• 20 – 50 gms of prepared sand us placed in a pan and is by an infrared heater for 2 – 3
minutes.
• Moulding sand is taken out and reweighed.
• % moisture can be calculated from the difference in the weights.

Figure 1.1: Moisture determining apparatus

Clay content test:

The method for determining the clay-content of moulding sands consists of agitating the sand
in water so as to separate the clay from the sand particles and then removing the clay which
remains suspended in water. The material which fails to settle within a period of 10 mins in
water at room temperature is designated as a clay substance.

1. Dry a small quantity of prepared moulding sand.

2. Separate 50 gms of dry moulding sand and transfer to a wash bottle.
3. Add 475 cc of distilled water and 25 cc of a 3% NaOH solution.
4. Using a stirrer, agitate the whole mixture for about 10 minutes.

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5. After settling down for about 10 mins, drain off the water from the bottle.
6. Clay is dissolved in water and is removed.
7. To the left out sand add more water and stir well and allow it to settle down.
8. Repeat the above steps until the water above the sand is clear.
9. This assures that the clay is completely removed.
10. Dry out the sand.
11. Difference in weights gives the % clay in the moulding sand.

Grain fineness test:

Figure 1.2: Grain fineness tester

This test determines
a) Grain size
b) Distribution
c) Grain fineness
The instrument consists of 11 standard sieves and a shaker. The top is the coarsest and the
bottom finest. To obtain the GRAIN FINENESS NUMBER, % of each sieve size is multiplied by
a factor and added. The result is ÷ total % of sand grains retained.

Permeability test
Permeability is the property of moulding sand which permits the escape of steam & other
gases generated during pouring.
Permeability depends on:
• Grain size.
• Grain shape.
• Grain distribution.
• Binder & its content.
• Degree of ramming.
• Water content of the sand.

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Since permeability is the property of moulded sand, a standard specimen is to prepared first.
This is done by using the Sand Rammer.

Figure 1.3: Sand specimen rammer

Permeability tester
Consists of:
• Inverted Bell jar, which floats in a water seal and can permit 2000 cc of air flow.
• Specimen tube, to hold the sand specimen.
• Manometer to read the Air pressure.
• 2000 cc of air held in the inverted bell jar is forced to pass through the sand specimen.
• A situation comes when the air entering the specimen equals the air escaped through
the specimen. (Constant Pr. ‘P’ on manometer).
• Simultaneously, measure the time ‘T’ for 2000 cc of air to pass through the specimen.

Figure 1.4: Permeability tester

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V H
Permeability number =
P  AT
Where,
V = volume of air passed through the specimen =2000 cc.
H = height of the specimen = 5.08 cm.
A = area of the specimen = 20.268 cm 2
T = time (mts) taken for 2000 cc to pass through the specimen.
P = pressure (gms/cm 2 ) recorded by the manometer.

Strength test
The following tests are conducted on foundry sands:
a) Compression
b) Tensile
c) Shear
d) Transverse (Bending)
Testing is done on a Strength Tester

Figure 1.5: Strength tester machine

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Figure 1.6: Shapes for strength tester

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