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Unit-1: Introduction to manufacturing process
Casting Process: Introduction : Concept of Manufacturing process, its
importance.
Classification of Manufacturing processes. Introduction to Casting
process & steps involved.
Varieties of components produced by casting process. Advantages &
Limitations of casting process.
Patterns: Definition, functions, Materials used for pattern, various
pattern allowances and their importance. Classification of patterns.
Binder: Definition, Types of binder used in moulding sand.
Additives: Need, Types of additives used.
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Classification of manufacturing process
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Classification of manufacturing process
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Types of production systems
Mass production / continuous flow process
Batch production
Job shop production
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Sand casting
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Sand casting
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Sand casting
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Rolling
Hot-rolling
Cold-rolling
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http://www.youtube.com/watch?v=6xnKmt_gsLshttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=wBXexkRsAJghttp://www.youtube.com/watch?v=6xnKmt_gsLshttp://www.youtube.com/watch?v=6xnKmt_gsLshttp://www.youtube.com/watch?v=6xnKmt_gsLs8/21/2019 introductiontomanufacturingprocess-131218044420-phpapp02
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hydraulic
piston
chamber
chamber
stock
die
extruded shape
hydraulic
piston
chamber
chamber
stock
die
extruded shape
hydraulic
piston
chamber
chamber
stock
die
extruded shape
Extrusion: Schematic, Dies
Exercise: how can we get hollow parts?
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Shearing
A large scissors action, cutting the sheet along a straight line
Main use: to cut large sheet into smaller sizes for making parts.
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Punching
Cutting tool is a round/rectangular punch,that goes through a hole, or die of same shape
F t X edge-length of punch X shear strength
Punch
die
sheet
crack
(failure in shear)
clearance
die
piece cut away, or slug
t
F t X edge-length of punch X shear strength
Punch
die
sheet
crack
(failure in shear)
clearance
die
piece cut away, or slug
t
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Lathe
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Lathe operation ( Turning)
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Drilling operation ( Drilling)
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Milling operation ( Drilling)
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Grinding operation
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Water jet machining
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Electric discharge machining
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Electro chemical machining
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Plasma arc machining
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Welding operation
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Riveting operation
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Soldering operation
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Factors to be considered for selecting a
production process
a) Shape and size to be produced - For products with simple
shape, machining is best suited. But for complex and intricateshapes, casting is preferred. The size of the product is also animportant factor. For example, 'long' products such as rails or'thin' products such as car-body panels can be best made byforming process compared to others.
(b) Quantity to be produced - Both machining and casting canbe used for producing large quantity products, but are notsuitable for small quantity products, as they are noteconomical.
(c) Type of material - Materials possess various properties like
ductility, hardness, toughness, brittleness etc. Hard materialscannot be machined easily. Brittle materials cannot bemechanically worked (Forming process). In such cases,casting is preferred.
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b d d f l
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Factors to be considered for selecting a
production process
(d) Surface finish and dimensional accuracy - Casting with expendable
moulds does not yield good surface finish. However," if casting
process is selected, it should be followed by machining process to
obtain the desired surface finish and dimensional tolerance.
(e) Quality and property requirements - A defect-free product withspecific properties serve its purpose for long life. Properties of cast
material are generally less when compared to that of mechanically
worked materials. Also, casting gives a lot of defects. Hence, a process
that gives better properties and quality should be selected.
(f) Cost of the product - Customers often demand for products with more
features and performance at reduced prices. Hence, a low cost
production process should be selected, but at the same time, see that
no compromise is made in terms of quality.
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CASTING PROCESS
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Terms involved in casting
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Terms involved in casting process
Mould box (flask): It is usually a metallic
frame used for making and holding a sandmould. The mould box has two parts: the
upper part called 'cope', and the lower
part called 'drag'.
Parting line/parting surface: It is the zoneof separation between cope and drag
portions of the mould in sand casting.
Sprue:It is vertical passage through which the molten metal
will enter the gate.
Pouring basin: The enlarged portion of the sprue at its top
into which the molten metal is poured.
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Terms involved in casting process Gate/ingate: It is a short passage way which
carries the molten metal from the runner/
sprue into the mould cavity.
Riser: A riser or feed-head is a vertical
passage that stores the molten metal and
supplies (feed) the same to the casting as it
solidifies.
Gate/ingate: It is a short passage way which carries the molten metal from the
runner/ sprue into the mould cavity.
Riser: A riser or feed-head is a vertical passage that stores the molten metal
and supplies (feed) the same to the casting as it solidifies.
Mould cavity: The space in a mould that is filled with molten metalto form the
casting upon solidification.
Core: A core is a pre-formed (shaped) mass of sand placed in the mould cavity
to form hollow cavities in castings.
Core print: It is a projection attached to the pattern to help for support and
correct location of core in the mould cavity.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 30
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STEPS INVOLVED IN MAKING A CASTING
The basic steps in making a casting are:
(a) Pattern making
(b) Mould preparation (including gating and risering)
(c) Core making
(d) Melting and Pouring
(e) Cleaning and Inspection
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a) Pattern making
A pattern is a replica of the object to be cast.
It is used to prepare a cavity into which the molten
metal is poured.
A skilled pattern maker prepares the pattern using
wood, metal, plastic or other materials with the helpof machines and special tools.
Many factors viz., durability, allowance for shrinkage
and machining etc., are considered while making apattern.
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b) Mould preparation
Mould preparation involves forming a cavity by packing
sand around a pattern enclosed in a supporting metallicframe called 'flask' (mould box).
When the pattern is removed from the mould, an exact
shaped cavity remains into which the molten metal is
poured.
Gating and riseringare provided at suitable locations in
the mould.
Gating - Passage through which molten metal flows and enter the mouldcavity.
Risering- A reservoir of molten metal connected to the mould cavity to
supply additional metal so as to compensate for losses due to shrinkage, as
the metal solidifies.
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c) Core making
In some cases, a hole or cavity is required in the
casting.
This is obtained by placing a core in the mould
cavity.
The shape of the core corresponds to the shape
of the hole required.
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d) Melting and Pouring
Metals or alloys of the required composition are
melted in a furnace and poured into the mould
cavity.
Many factors viz., temperature of molten metal,
pouring time, turbulence etc., should be consideredwhile melting and pouring.
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e) Cleaning and Inspection
After the molten metal has solidified and cooled, the
rough casting is removed from the mould, cleaned
and dressed.
This involves removing cores, adhered sand particles,
gating and risering systems, fins, blisters etc., fromthe casting surface.
then sent for inspection to check for dimensions or
any defects like blow holes, cracks etc.
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Procedure for making the casting
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Components Produced by
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Components Produced by
Casting Process
Casting is the first step and the primary process forshaping any material.
All materials have to be cast before it is put to use.
The ingotsproduced by casting process are used as
raw material for secondary processeslike machining,
forging, rolling etc.
More than 90 %of all manufactured goods and capital
equipment use castings for their manufacture. To list the components produced by casting is an
endless process. A few major components produced by
casting are given below.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 41
Components Produced by Casting Process
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Components Produced by Casting Process
Automotive sector - Nearly 90 % of the parts in automobiles are-
manufactured by castings. A few parts include brake drum,
cylinder, cylinder linings, pistons, engine blocks, universal joints,rocker arm, brackets etc.,
Aircraft- Turbine blades, casing etc.
Marine propeller blades.
Machining- Cutting tools, machine beds, wheels and pulleys,blocks and table for supports etc.
Agriculture and rail road equipments.
Pumps and compressors frame, bushings, rings, pinion etc.
Valves, pipes and fittings for construction work.
Camera frames, parts in washing machine, refrigeratorsand air-
conditioners.
Steel utensils and a wide variety of products.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 42
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Advantages of casting process
Large hollow and intricate shapes can be easily cast.
Quick process, and hence suitable for mass production.
No limit to size and shape. Parts ranging from few millimeters to
meters and few grams to tons can be cast efficiently and
economically.
Better dimensional tolerances and surface finish can be obtained
by good casting practice.
Castings exhibit uniform properties in all the directions -
longitudinal, lateral and diagonal. The casting process is usually the cheapest process.
Unrelieved internal stresses are absent in cast components.
Certain metals and alloys can be manufactured by means of
casting only, e.g., Phosphor-Bronze.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 43
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Limitations of casting process
Presence of defects in cast parts is a major disadvantage.
Casting process is not economical for small number of parts.
Properties of cast materials are generally inferior when
compared to those made by machining or forging process.
Casting process mostly deals with elevated temperatures.
There are limitations regarding thin sections.
Casting process is not suitable for very small number of
components.
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INTRODUCTION TO PATTERN MAKING
A pattern is a mold forming tool in the hands of foundry men.
A pattern is a model or the replica of the object to be cast.
Except for the various allowances a pattern exactly
resembles the casting to be made. A pattern is required even if one object has to be cast.
A patternmay be defined as a model or form around which
sand is packed to give rise to a cavity known as mold cavity
in which when, molten metal is poured, the result is the CASTOBJECT.
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Difference between pattern and casting
The main difference between a pattern and the casting is their dimensions.
A pattern is slightly larger in size as compared to the casting, becauseapattern,
carries Shrinkage allowance, it may be of the order of 1 to 2 mm/ 100
mm.
is given a Machining allowance to clean and finish the required surfaces.
carries a Draft allowance of the order of 1 and 3 degrees for externaland internal surfaces respectively
carries core prints.
A pattern may not have all holes and slots which a casting will have. Such
holes and slots unnecessarily complicate a pattern and therefore can bedrilled in the casting after it has been made.
A pattern may be in two or three pieces whereas a casting is in one piece.
A pattern and the casting also differ as regards the material out of which
they are made.
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Functions of a patterns
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Functions of a patterns A pattern prepares a mold cavity for the purpose of making a casting.
A pattern may contain projections known as core prints if the casting
requires a core and need to be made hollow.
Runner, gates and risers (used for introducing and feeding molten
metal to the mold cavity) may form a part of the pattern.
A pattern may help in establishing locating points on the mold and
therefore on the casting with a purpose to check the castingdimensions.
Patterns establish the parting line and parting surfaces in the mold.
A pattern may help position a core (in case a part of mold cavity is
made with cores), before the molding sand is rammed. Patterns that are properly made and having finished and smooth
surfaces, reduce casting defects.
Properly constructed patterns minimize overall cost of the castings.
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P i l
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Pattern materials
The following factors assist in selecting proper pattern material:
The number of castings to be produced. Metal patterns are
preferred when the production quantity is large.
The desired dimensional accuracy and surface finish requiredfor the castings.
Nature of molding process i.e., sand casting, permanent mold
casting, shell molding, investment casting etc.
Method of molding i.e., hand or machine molding.
Shape, complexity and sizeof the casting.
Type of molding materials i.e., sand etc.
The high probability of changing the casting and hence the
pattern in near future.
Selection of pattern materials
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M t i l f ki tt
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Materials for making patterns
Patterns may be constructed out of the following
materials.
(a) Wood (b) Metal
(d) Plastic (d) Plaster (POP)
(e) Wax
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WOOD
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WOOD The most common materials for making patterns for sand casting is the wood.
Advantages
Inexpensive. Easily available in large quantities.
Easy to machine and to shape to different configurations and forms
Easy to join to acquire complex and large pattern shapes
Light in weight
Easy to obtain good surface finish
Wooden patterns can be preserved for quite long times with the help of
suitable wood preservatives.
Limitations
Wooden patterns are susceptible to shrinkage and swelling.
They possess poor wear resistance.
They are abradedeasily by sand action.
They absorb moisture, consequently get deformed and change shape and size.
They cannot withstand rough handling.
They are weakas compared to metal patterns.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 50
M t l
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Metal
Metal patterns are employed where large number of
castingshave to be produced from the same patterns. Metal patterns are cast from wooden patterns.
The different metals and alloys used for making
patterns are,
Aluminium and Aluminium alloys
Steel
Cast Iron
Brass White Metal
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Advantages of Metal Patterns
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Advantages of Metal Patterns Unlike wooden patterns, they do not absorb moisture. They retain their
shape.
They are more stronger and accurate as compared to wooden patterns.
They possess life much longer than wooden patterns.
They can withstand rough handling.
They do not distort
They possess greater resistance to abrasion. They have accurate
dimensional tolerances. They are far stable under different environments. It is easy to obtain smooth surface finish.
They possess excellent wear resistance and strength to weight ratio.
Limitations of Metal Patterns
Expensiveas compared to wood patterns. Are not easily repaired e.g. (Aluminium patterns).
Ferrous patterns get rusted.
They (ferrous patterns) are heavierthan wooden patterns,
They cannot be machined so easily as wooden ones.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 52
Plastic
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Plastic
Advantages
Durable Provides a smooth surface.
Moisture resistant.
A plastic pattern does not involve any appreciable change in its size or
shape.
Lightweight.
Wear and corrosion resistant.
Provides good surface finish.
It possesses low solid shrinkage.
Limitations Plastic patterns are fragileand thus light sections may need metal
reinforcements.
Plastic patterns may not work well when subject to conditions of severe
shock as in machine moulding.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 53
PLASTER
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PLASTER
Advantages
can be easily worked by using wood working tools. Intricate shapes can be cast without any difficulty.
It has high compressive strength (up to 285 kg/cm2)
Disadvantages
Can be used for small castings only
Plaster Patterns Material: Plaster patterns may be
made out of Plaster of Paris or Gypsum cement.
Applications: Plaster is used for making (i) Small
and intricate patterns, and (ii) Core boxes.
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WAX
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WAX
Advantages
Wax patterns provide very good surface finish
They impart high accuracy to the castings.
After being molded, the wax pattern is not taken out of
the mold like other patterns; rather the mold is
inverted and heated; the molten wax comes out and/oris evaporated. Thus there is no chance of the mold
cavity getting damaged while removing the pattern.
Applications
Wax patterns find applications in Investment
casting process.
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PATTERN ALLOWANCES
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PATTERN ALLOWANCES
A pattern is always larger in size as compared to
the final casting, because it carries certainallowances.
The various pattern allowances are below
(a) Shrinkage or contraction allowance.
(b) Machining or Finish allowance.
(c) Draft or Taper allowance.
(d) Distortion or camber allowance.(e) Shake or rapping allowance.
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Sh i k All
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Shrinkage Allowance Almost all cast metals shrink or contract volumetrically after solidification and
therefore to obtain a particular sized casting, the pattern is made oversize by
an amount equal to that of shrinkage or contraction.
Different metals shrink at different rates because shrinkage is the property of
the cast metal or alloy.
The metal shrinkage depends upon
The cast metal or alloy.
Pouring temperature of the metal or alloy.
Casting dimensions(size).
Casting design aspects.
Molding conditions (i.e., mold materials and molding methods
employed).
Cast iron poured at higher temperatures will shrink more than that poured at
lower temperature.
Wood patterns used to make metallic patterns are given double allowance; one
for the shrinkage of the metal of the pattern and the other for that of metal to
be cast.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 57
Machining Allowance
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Machining Allowance A casting is given an allowance for machining, because
Castings get oxidized in the mold and during heat treatment; scales etc., thus formed
need to be removed.
It is intended to remove surface roughness and other imperfectionsfrom the castings.
It is required to achieve exact casting dimensions.
How much extra metal or how much Machining allowance should be provided,
depends upon:
Nature of metal i.e., ferrous or non-ferrous. Ferrous metals get scaled whereas non-ferrous ones do not.
Size and shape of the casting. Longer castings tend to warp and need more material (i.e., allowance) tobe added to ensure that after machining the casting will be alright.
The type of machining operation (i.e., grinding, turning, milling, boring etc.) to be employed forcleaning the' castings. Grinding removes much lesser metal as compared to turning.
Casting conditions i.e., whether casting conditions result in a rough casting or a semi-finished one. Castingconditions include the characteristics of mold-materials etc.
Molding process employed. Die casting produces parts which need little machining (allowance) whereassand-casting, require more machining allowance.
Number of cuts to be taken. Machining allowance is directly proportional to the number of cuts required for finishingthe casting.
The degree of surface finish desired on the cast part.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 58
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Draft or Taper Allowance It is given to all surfacesperpendicular to the parting
line.
Draft allowance is given so that the pattern can be easily
removedfrom the molding material tightly packed
around it without damaging the mold cavity.
The amount of Taper depends upon Shape and size (length) of the pattern in the depth direction in contact with
the mold cavity.
Molding method.
Mold materials.
Draft allowance is imparted on internal as well asexternal surfaces; of course it is more on internal
surfaces.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 59
Fig. shows two patterns one with taper allowance and the
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g p p
other without it. It can be visualized that it is easy to draw the
pattern having taper allowance, out of the mold without
damaging mold walls or edges.
Taper on external surfaces = 10 to 25 mm/metre.
Taper on internal surfaces = 40 to 65 mm/metre,9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 60
Distortion Allowance
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Distortion Allowance A Casting will distort or warp if:
it is of irregular shape,
all its parts do not shrink uniformly i.e., some parts shrink while others arerestricted from doing so,
it is U or V-shaped,
it has long, rangy arms as those of the propeller strut for the ship,
it is a long flat casting,
the arms possess unequal thickness,
one portion of the casting cools at a faster rate as compared to the other,
etc.
Distortion can be practically eliminated by providing an allowance
and constructing the pattern initially distorted i.e., outsize in theopposite direction so that the casting after cooling neutralizes the
initial distortion given on the pattern and acquires the correct shape.
The amount of distortion allowance may vary from 2 to 20 mm
depending upon the size, shape and material of the casting.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 61
Sh k All
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Shake Allowance A pattern is shaken by striking the same with a wooden
piece from side to side. This is done so that the pattern isloosened a little in the mold cavity and can be easily
removed.
In turn, therefore, shaking enlarges the mold cavity
which results in a bigger sized casting.
Shake allowance is normally provided only to large
castingsbecause it is negligible in case of small castings
and is thus ignored. The magnitude of shake allowance can be reduced by
increasing the taper.
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TYPES OF PATTERNS
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F l i i l ki d f f ki i
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For selecting a particular kind of pattern for making a casting,
one may consider the following points:
Quantityof castings to be produced.
The size and the complexity of the shape of the casting to be
produced.
Type of molding method to be used (i.e., hand or machine
molding).
Problems associated with the molding operation such as
withdrawing the pattern from the mold etc.
Other difficulties resulting from poor casting design or pattern
design.
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The different types of patterns commonly used
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The different types of patterns commonly used
are:
One piece(Solid) pattern
Split pattern
Loose piece pattern
Match plate pattern
Cope and Drag pattern
Sweep pattern
Gated pattern
Skeleton pattern
Follow board pattern.
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O Pi ( lid) P tt
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One Piece (solid) Pattern
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One Piece (solid) Pattern
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One Piece (solid) Pattern It is the simplest type of pattern.
As the name suggests the pattern ismade from one piece and does not
contain loose pieces or joints.
It is inexpensive. It is used for making a few large size simple castings
One piece pattern is usually made up of wood or
metaldepending upon the quantity of castings to be
produced.
For making the mold, one piece pattern is
accommodated either in the cope or in the drag.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 67
Split Pattern
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Split Pattern
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Split Pattern
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Split Pattern Patterns of intricate (shaped) castingscannot be made in one piece
because of the inherent difficulties associated with the molding
operations (e.g. withdrawing the pattern from the mold etc.) , suchpatterns are, then, made as split or two piece patterns.
The upper and the lower parts of the split pattern are
accommodated in the cope and drag portionsof the mold
respectively. Dowel pins are used for keeping the alignment between the two
parts of the pattern.
The parting (surface or)line of the pattern forms the parting
(surface or) line of the mold. Patterns for still more intricate castings are made in more than two
pieces for facilitating their molding and withdrawing.
A pattern having three pieces will require a three piece flask for the
molding purposes9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 69
Loose Piece Pattern
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Loose Piece Pattern
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Loose Piece Pattern
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Certain patterns cannot be withdrawn once they are
embedded in the molding sand. Such patterns are
usually made with one or more loose pieces
Piecesfor facilitating their removal from the molding
box and are known as loose piece patterns.
Loose parts or pieces remain attached with the mainbody of the pattern, with the help of dowel pins.
The main body of the pattern is drawn firstfrom the
molding box and thereafter the loose parts are
removed, the result is the mold cavity.
Loose piece patterns involve more labour and consume
more timein the molding operation.
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Match Plate Pattern
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Match Plate Pattern
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Match Plate Pattern
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Match Plate Pattern A match plate pattern consists of a match plate, on
either side of which each half of (a number of) splitpatterns is fastened.
A number of different sized and shaped patterns may be
mountedon one match plate.
The match plate with the help of locator holes can be
clamped with the drag.
The match plate has runner and gates also attached with
it. After the cope and drag have been rammed with the
molding sand, the match plate pattern is removed from
in between the two (i.e., cope and drag.)9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 73
Match Plate Pattern
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Match Plate Pattern Cope and drag are then assembled and this completes
the mold. Patterns, match plate, runner and gatesall may be
made up of aluminium, because it is light and
relatively inexpensive.
Match plate patterns are normally used in machine
molding.
Match plate patterns are preferred for producing small
castings on mass scale. They produce accurate castings and at faster rates.
Piston rings of I.C. engines are produced with the help
of match plate patterns.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 74
Sweep Pattern
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Sweep Pattern
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Sweep Pattern
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Sweep Pattern A sweep pattern is just a form made on a wooden board
which sweeps the shapeof the casting into the sand all
around the circumference. The sweep pattern rotates aboutthe post.
Once the mold is ready, sweep pattern and the post can be removed
Sweep pattern avoids the necessity of making a full, large
circular and costly three dimensional pattern.
Making sweep pattern saves a lot of time and labour as
compared to making a full pattern.
A sweep preferred for producing large castings of circularsections and symmetrical shapes.
The manufacture of large kettles of cast iron requires a sweep
pattern.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 76
Gated Pattern
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Gated Pattern
castings
Gating system
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Gated Pattern
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Gated patterns are usually made of metal which
increases their strength and reduces the tendency to
warp.
The sections connecting different patterns serve as
runner and gates. This facilitates filling of the mold
with molten metal in a better manner at the sametime eliminates the time and labour otherwise
consumed in cutting runners and gates.
A gated pattern can manufacture many castings at
one timeand thus it is used in mass productionsystems.
Gated patterns are employed for producing small
castings.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 78
Skeleton Patten
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Skeleton Patten
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A skeleton pattern is the skeleton of a desired shape. The skeleton
frame is mounted on a metal base.
The skeleton is made from wooden strips and is thus a woodenframework.
The skeleton pattern isfilled with sand and is rammed.
A strickle(board) assists in giving the desired shape to the sand
and removes extra sand. If the object is symmetricallike a pipe, the two halves(of the pipe)
can be molded by using the same pattern and then the two molds
can be assembled before pouring the molten metal.
Skeleton patterns are employed for producing a few large castings. A skeleton pattern is very economical as compared to a solid
pattern, because it involves less material costs.
Castings for turbine castings, water pipes, channels, etc., are
made with the help of skeleton patterns.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 80
Follow Board Pattern
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Follow Board Pattern
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Follow Board Pattern
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Follow Board Pattern A follow board is a wooden board and is used for
supporting a pattern which is very thin and fragile andwhich may collapse under the pressure when the sand
above the pattern is being rammed.
With the follow board support under the weak pattern,
the drag is rammed, and then the follow board iswithdrawn.
The rammed drag is inverted, cope is mounted on it and
rammed. During this operation pattern remains over the
inverted drag and gets support from the rammed sand of
the drag under it.
Ultimately, the pattern is removed and the cope and
drag are assembled.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 82
MOLDING SAND BINDERS
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Binders produce cohesion between the molding sand grains in the
green or dry state (or condition).
Binders give strength to the molding sand so that it can retain its
shape as mold cavity.
Binders (to the molding sands) should be added as optimal
minimum.
Increasingbinder content reduces permeability of molding sand.
Increasing binder content, increases green compression strength
up to a limit; after which green compression strength remains
practically unchanged with further increase in binder content.
Clay binders are most commonly used for bonding molding sands.
The best clay is one which imparts the optimum combination of
bonding properties, moisture, life and cost of producing the
required casting.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 83
MOLDING SAND BINDERS
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Clay binders are most commonly used for bonding molding sands.
Clay binders can be classified as:
Fire clay
Bentonite
Sodium montmorillonite
Calcium montmorillonite
Illite Kaolinite
Bentonite: The most commonly used clay binders are Bentonites as they produce
strongest bonds in foundry molding sands.
Bentonite deposits are available in India in Rajasthan and Bihar
Bentonites are the weathered product of volcanic ash and are soft creamy
white powders.
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MOLDING SAND BINDERS
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Fire Clay:
Fire clay is a refractory clay usually found in the coal measures.
Fire clay particles are about 400 times as largeas compared to those of Bentonite ;hence the same percentages of fire clay produce lower strengths.
Illite
Illite is the decomposition product of micaceous materials due to weathering.
Illite is found in natural molding sands.
Illite has softening point of about 2500F.
Illite does not swell in the same way as bentonite but gives reasonable strength.
Illite particles have thickness and width of 20 and 100-250 milli-microns respectively.
Kaolinite
Kaolinite is the residue of weathered granite and basalt. Kaolinite binder has its composition 60% kaolinite, 30% illite and 10% quartz,
Kaolinite gets Very low swelling due to water and is non-gel forming.
Kaolinite particles possess thickness and width of 20 and 100-250 milli-microns
respectively.
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WATER
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The amount of water may vary from 1.5 to 8%.
water is responsible for the bonding action of clays.
Water activates the clay in the sand and the clay-sand mixture developsstrength and plasticity.
Water added to the sand mixture, partly gets adsorbed by clay and partly
remains free and is known as Free Water.
The absorbed water is responsible for developing proper bond and the green
strength.
The free water acts as a lubricant,
It increases plasticity
It improves moldability, but It reduces strength of the sand mixture.
For a given type of clay and its amount, there is an optimum required watercontent.
Too little water will not develop proper strength and plasticity.
Too much water will result in excessive plasticity and dry strength.
The amount of water required to develop the optimum properties can be
found out experimentally.9/18/2014 Hareesha N G, Asst. Prof, DSCE, BLore 86
ADDITIVES
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The basic constituents of molding sand mixture are;
Sand
binder and
water
Materials other than the basic ingredients are also added to
molding sand mixtures, of course in small quantities, in order to
enhancethe existing properties. To develop certain other properties.
to give special qualities like resistance to sand expansion, defects etc.
Some of the additive materials along are given below.
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Facing materials:
F i t i l t d t bt i th d l f f ti
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Facing materials tend to obtain smoother and cleaner surfaces of castings
and help easy peeling of sand from the casting surface during shake out.
A few facing materials are
Sea coal Graphite
Coke
Silica floor
Cushion materials:
Cushion materials burn when the molten metal is poured and thus give rise
to space for accommodating the expansion of silica sand at the surfaces of
mold cavity.
In the absence of cushion materials, large flat surfaces of castings may
buckle due to thermal expansion of silica sand grains.
A few cushion materials are:
Wood floor
Cellulose