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Casting Process
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CASTINGPATTERNMAKING:
In pattern making, a physical model ofcasting, i.e. a pattern is used to make the
mold. The mold is made by packing
some readily formed aggregated
materials, like molding sand, around the
pattern. After the pattern is withdrawn, its
imprint leaves the mold cavity that is
ultimately filled with metal to become the
casting.
n case, the castings is required to behollow, such as in the case of pipe
fittings, additional patterns, known as
cores, are used to develop these cavities.
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COREMAKING& MOLDING:
In core making, cores are formed,
(usually of sand) that are placed
into a mold cavity to form the
interior surface of the casting.
Thus the annul space between themold-cavity surface and the core
is what finally becomes the
casting.
Molding is a process that consistsof different operations essential to
develop a mold for receiving
molten metal
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ALLOYMELTINGANDPOURING:
Melting is a process of preparing
the molten material for casting. It
is generally done in a specifically
designated part of foundry, and
the molten metal is transported tothe pouring area wherein the
molds are filled
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CASTINGCLEANING:
The casting is separated from the mold
and transported to the cleaningdepartment.
Burned-on sand and scale are removed.
Excess metal is removed (Fins, wires,
parting line fins, and gates).
Subsequently the casting can be
upgraded using welding or other such as
procedures.
Final testing and inspection to check for
any defects
Advantages:Improves the surface appearance and finish of casting
Improves overall quality and functionality by removing impurities, such as
sand, scale and excess metal
Finally the sand from the mold is separated and processed through a
reclamation system for further use.
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INDUSTRIALPROCESSDESCRIPTION
The metal casting process has been divided intothe following five major operations:
Obtaining the Casting Geometry:The process is referred as the study of thegeometry of parts and plans, so as to improve
the life and quality of casting.
Advantages of Good Casting GeometryReduces defects, post casting operations, andrejected castings
Significantly reduce energy and environmentalimpacts
Saves energy
Improves overall quality and life of casting
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A key part of designing a mold involves the use ofcores. Cores are preformed masses of bondedsand or some other material that are used to makethe internal passageways of a casting. Castings
may require a single core, a complex assembly ofcores or no cores at all. Like castings, cores aremade in a mold, called a coldbox.
Typically cores are made of sand and may becombined with other materials that bind the sand
together. Metal cores are used in permanent moldand diecasting processes. The type of cores usedin each metalcasting process will also be part ofyour decision making process.
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TYPES OF MOLDING PROCESS
1 Expendable Mold1.1 Permanent Pattern
1.1.1 Sand Casting
1.1.2 Plaster
Molding
1.2 ExpendablePattern
1.2.1 Lost Foam
1.2.2 Lost Wax
(investmentcasting)
1 Permanent Mold1.1 Die
1.1.1 Hot Chamber
1.1.2 Cold Chamber
1.1.3Thixotropic
Mold prepertation =) metal heating =) pouring =) cooling =) processing
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SAND CASTING
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The set of channels through which a molten metal flows
to the mold cavity is called gating system.
Typical gating system consists of a pouring cupand a
spruereceiving the poured melt, runner
a channelthrough which the melt is supplied to the gates through
which the molten metal enters the mold cavity.
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INVESTMENT CASTING
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EXPANDABLEMOLDPERMANENTPATTERN
SHELL MOLDING
Shell moulding is a process for producing simple or complex near
net shape castings, maintaining tight tolerances and a high degree
of dimensional stability. Shell moulding is a method for making high
quality castings. These qualities of precision can be obtained in a
wider range of alloys and with greater flexibility in design than die-
casting and at a lower cost than investment casting.
INVESTMENT CASTING
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Shell molding
Advantages
Better surface finish
Better dimensional tolerances.
Reduced Machining. Less foundry space required.
Semi skilled operators can handle the process.
The process can be mechanized.
Disadvantages
The raw materials are relatively expensive.
The process generates noxious fumes which must be removed.
The size and weight range of castings is limited.
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EXPANDABLEMOLDPERMANENTPATTERN
LOST FOAM CASTING
INVESTMENT CASTING
Lost foam casting(LFC) is a type of investment casting
process that usesfoam patternsas a mold. The method
takes advantage of the properties of foam to simply and
inexpensively create castings that would be difficult to
achieve using other casting techniques.
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EXPANDABLEMOLDPERMANENTPATTERN
LOST FOAM CASTING
Lost foam casting(LFC) is a type of investment casting
process that usesfoam patternsas a mold. The method
takes advantage of the properties of foam to simply and
inexpensively create castings that would be difficult to
achieve using other casting techniques.
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Lost foam casting
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Lost foam, is similar to Investment or Lost wax, in
that the medium, or pattern device, is Expendable,
they melt or evaporate away, leaving the cast part.
They both have advantages, for the type of function
they were designed. One Process's advantage,
could be the other Process's weak area.
These points are brought up in the text portion of
Education Section.
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PERMANENT MOLD
DIE CASTINGLiquid metal injected into reusable steel mold, or die,
very quickly with high pressures .
Die casting is a process in which the molten metal is
injected into the mold cavity at an increased pressureThe mold used in the die casting process is called a die.
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In a cold chamberprocess, the molten metal is ladled intothe cold chamber for each shot. There is less time exposure ofthe melt to the plunger walls or the plunger. This is particularlyuseful for metals such as Aluminum, and Copper (and itsalloys) that alloy easily with Iron at the higher temperatures.
PERMANENT MOLDDIE CASTING
COLD CHAMBER
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In a hot chamberprocess the pressure chamber is connected to
the die cavity is immersed permanently in the molten metal. The inlet
port of the pressurizing cylinder is uncovered as the plunger moves
to the open (unpressurized) position. This allows a new charge of
molten metal to fill the cavity and thus can fill the cavity faster thanthe cold chamber process. The hot chamber process is used for
metals of low melting point and high fluidity such as tin, zinc, and
lead that tend not to alloy easily with steel at their melt temperatures.
PERMANENT MOLDDIE CASTING
HOT CHAMBER
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Manifacturing techniques
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TERMSOFCASTNG
Riser: A column of metal placed in the mold to feed
the casting as it shrinks and solidifies. Also known
as a "feed head."
Riser:A column of metal placed in the mold to feed the casting as it shrinks andsolidifies. Also known as a "feed head."
Runner: The channel through which the molten metal is carried from the sprue to the
gate.
Cores:A separated part of the mold, made of sand and generally baked, which is usedto create openings and various shaped cavities in the casting.
Gate:A channel through which the molten metal enters the casting cavity.
Sand:A sand which binds strongly without losing its permeability to air or gases.
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TERMSOFCASTNG
Binders: Materials used to hold molding sand together.
Parting Line: Joint where mold separates to permit removal of the pattern. The axe
which shows how and where to open the mold
Centrifugal Casting: Process of filling molds by pouring metal into a mold which isspinning or revolving about an axis. Cast iron pipe can be created using this method.
Chaplet:A metal support used to hold a core in place in a mold. Not used when
a core print will serve.
Draft: Slight taper given to a pattern to allow drawing from the sand.
Pouring: Filling the mold with molten metal.
Shrinkage: The decrease in volume when molten metal solidifies.
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SELECTINGTHERIGHTMETALCASTING
PROCESS
For any Metal Casting Process, selection of right alloy, size,shape, thickness, tolerance, texture, and weight, is very vital.
Special requirements such as, magnetism, corrosion, stressdistribution also influence the choice of the Metal CastingProcess.
Views of the Tooling Designer; Foundry / Machine House needs,
customer's exact product requirements, and secondaryoperations like painting, must be taken care of before selectingthe appropriate Metal Casting Process.
Tool cost.
Economics of machining versus process costs.
Adequate protection / packaging, shipping constraints,
regulations of the final components, weights and shelf life ofprotective coatings also play their part in the Metal Castingprocess.
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Advantages Disadvantages Recommended
Application
Least Expensive in
small quantities (less
than 100)
Ferrous and non -
ferrous metals may be
cast
Possible to cast very
large parts.
Least expensive
tooling
Dimensional
accuracy inferior to
other processes,
requires largertolerances
Castings usually
exceed calculated
weight
Surface finish of
ferrous castings
usually exceeds 125
RMS
Use when
strength/weight
ratio permits
Tolerances,
surface finish and
low machining cost
does not warrant a
more expensive
process
SANDCASTING
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PERMANENTANDSEMI-PERMANENTMOLD
CASTING
Advantages Disadvantages Recommended
Application
Less expensive
than Investment or
Die Castings
Dimensional
Tolerances closer
than Sand Castings
Castings are dense
and pressure tight
Only non-ferrous
metals may be cast
by this process
Less competitive
with Sand Cast
process when three
or more sand cores
are required
Higher tooling cost
than Sand Cast
Use when
process
recommended for
parts subjected tohydrostatic
pressure
Ideal for parts
having low
profile, no coresand quantities in
excess of 300
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PLASTERCAST
Advantages Disadvantages Recommended
Application
Smooth "As Cast"
finish (25 RMS)
Closer dimensionaltolerance than Sand
Cast
Intricate
shapes and fine
details including
thinner "As Cast"
walls are possible
Large parts
cost less to cast than
by Investment
process
More costly than
Sand or Permanent
Mold-Casting
Limited number of
sources
Requires minimum
of 1 deg. draft
Use when parts
require smooth "As
Cast" surface finish
and closertolerances than
possible with Sand
or Permanent Mold
Processes
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INVESTMENTCAST
Advantages Disadvantages Recommended
Application
Close dimensional
tolerance
Complex shape, finedetail, intricate core
sections and thin walls
are possible
Ferrous and non-
ferrous metals may becast
As-Cast" finish (64 -
125 RMS)
Costs are higher than
Sand, Permanent
Mold or Plaster
process Castings
Use when
Complexity
precludes use of
Sand or PermanentMold Castings
The process cost is
justified through
savings in
machining orbrazing
Weight savings
justifies increased
cost
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DIECASTING
Advantages Disadvantages Recommended
Application
Good dimensional
tolerances are
possible
Excellent part-part
dimensional
consistency
Parts require a
minimal postmachining
Economical only in very
large quantities due to
high tool cost
Not recommended forhydrostatic pressure
applications
For Castings where
penetrant (die) or
radiographic inspectionare not required.
Difficult to guarantee
minimum mechanical
properties
Use when quantity of
parts justifies the high
tooling cost
Parts are not
structural and are
subjected to
hydrostatic pressure
Recommended