Casting Process. C ASTING P ATTERNMAKING C ASTING P ATTERNMAKING : In pattern making, a physical...

Casting Process

CASTİNG PATTERNMAKİNG :

In pattern making, a physical model of casting, 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 After the pattern is withdrawn, its imprint leaves the mold cavity that is ultimately filled with metal to become the casting.n case, the castings is required to be hollow, such as in the case of pipe fittings, additional patterns, known as cores, are used to develop these cavities.

COREMAKİNG & MOLDİNG : 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 the mold-cavity surface and the core is what finally becomes the casting.Molding is a process that consists of different operations essential to develop a mold for receiving molten metal

ALLOY MELTING AND POURING :

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 to the pouring area wherein the molds are filled

CASTING CLEANING :

•The casting is separated from the mold and transported to the cleaning department. •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.

INDUSTRIAL PROCESS DESCRIPTION The metal casting process has been

divided into the following five major operations:

Obtaining the Casting Geometry :The process is referred as the study of the geometry of parts and plans, so as to improve the life and quality of casting.

Advantages of Good Casting GeometryReduces defects, post casting operations, and rejected castings

Significantly reduce energy and environmental impacts

Saves energy Improves overall quality and life of casting

A key part of designing a mold involves the use of cores. Cores are preformed masses of bonded sand or some other material that are used to make the internal passageways of a casting. Castings may require a single core, a complex assembly of cores or no cores at all. Like castings, cores are made in a mold, called a coldbox.

Typically cores are made of sand and may be combined with other materials that bind the sand together. Metal cores are used in permanent mold and diecasting processes. The type of cores used in each metalcasting process will also be part of your decision making process.

TYPES OF MOLDING PROCESS

1 Expendable Mold1.1 Permanent Pattern

1.1.1 Sand Casting1.1.2 Plaster Molding

1.2 Expendable Pattern

1.2.1 Lost Foam1.2.2 Lost Wax (investment casting)

1 Permanent Mold1.1 Die

1.1.1 Hot Chamber1.1.2 Cold Chamber1.1.3Thixotropic

Mold prepertation =) metal heating =) pouring =) cooling =) processing

EXPANDABLE MOLDPERMANENT PATTERN

SAND CASTING

SAND CASTING

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 cup and a sprue receiving the poured melt, runner – a channel through which the melt is supplied to the gates through which the molten metal enters the mold cavity.

EXPANDABLE MOLDEXPANDABLE PATTERN

INVESTMENT CASTING

•Use gravity to fill the mold.•Mold is destroyed to remove casting•Metal flow is slow•Walls are much thicker than in die casting.•Cycle time is longer than die casting because of inability of mold material to remove heat.The investment casting process uses expendable patterns made of investment casting wax: The wax patterns are commonly prepared by injection molding technology which involves injection of wax into a prefabricated die having the same geometry of the cavity as the desired cast part.

INVESTMENT CASTING


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

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.


LOST FOAM CASTING

INVESTMENT CASTING

Lost foam casting (LFC) is a type of investment casting process that uses foam patterns as 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.


LOST FOAM CASTING

Lost foam casting (LFC) is a type of investment casting process that uses foam patterns as 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.

Lost foam casting

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.

PERMANENT MOLDDIE CASTING

Liquid 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 pressure The mold used in the die casting process is called a die.

In a cold chamber process, the molten metal is ladled into the cold chamber for each shot. There is less time exposure of the melt to the plunger walls or the plunger. This is particularly useful for metals such as Aluminum, and Copper (and its alloys) that alloy easily with Iron at the higher temperatures.

PERMANENT MOLD DIE CASTING

COLD CHAMBER

In a hot chamber process 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 than the 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 MOLD DIE CASTING

HOT CHAMBER

Manifacturing techniques

TERMS OF CASTING

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 and solidifies. 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 used to 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.

TERMS OF CASTING

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 is spinning 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.

SELECTING THE RIGHT METAL CASTING 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, stress distribution also influence the choice of the Metal Casting Process.

Views of the Tooling Designer; Foundry / Machine House needs, customer's exact product requirements, and secondary operations like painting, must be taken care of before selecting the 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 of protective coatings also play their part in the Metal Casting process.

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 larger tolerances

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

SAND CASTİNG

PERMANENT AND SEMI-PERMANENT MOLD CASTING


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 to hydrostatic pressure

Ideal for parts having low profile, no cores and quantities in excess of 300

PLASTER CAST


Smooth "As Cast" finish (25 RMS)

Closer dimensional tolerance 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 closer tolerances than possible with Sand or Permanent Mold Processes

INVESTMENT CAST


Close dimensional tolerance

Complex shape, fine detail, intricate core sections and thin walls are possible

Ferrous and non-ferrous metals may be cast

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 Permanent Mold Castings

The process cost is justified through savings in machining or brazing

Weight savings justifies increased cost

DİE CASTİNG


Good dimensional tolerances are possible

Excellent part-part dimensional consistency

Parts require a minimal post machining

Economical only in very large quantities due to high tool cost

Not recommended for hydrostatic pressure applications

For Castings where penetrant (die) or radiographic inspection are 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

Casting Process. C ASTING P ATTERNMAKING C ASTING P ATTERNMAKING : In pattern making, a physical...

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