MATA KULIAH PROSES PRODUKSI JURUSAN TEKNIK INDUSTRI ITENAS

SEMESTER GANJIL 2008/2009

The Fundamentals of Metal Casting

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1. Definition

Casting is process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity.

The principle of casting seems simple: melt the metal, pour it into mold and let it freeze.

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2. Casting ingots & Casting of the shape

Casting ingots associated with the primary metals industries, simple in shape and intended for subsequent reshaping by processes such rolling or forging.

Shape casting involves the production of more complex geometries that are much closer to the final desired shape of the part or product.

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3. Casting capabilities and advantages

Casting can be used to create complex part geometries, including both external and internal shape.

Some casting process are capable of producing parts to net shape. Other casting processes are near net shape.

Casting can be used to produce very large parts.

The casting process can be performed on any metal that can be heated to the liquid state.

Some casting methods are quite suited to mass production.

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4. Casting disadvantages

Limitations on mechanical properties.PorosityPoor dimensional accuracy and surface finish

for some casting processSafety hazard to human when processing hot

molten metals.Environmental problems.

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5. Mold

The mold contains a cavity whose geometry determine the shape of the cast part.

The actual size and shape of the cavity must be designed slightly oversized to allow for shrinkage that occurs in the metal during solidification and cooling.

Molds are made of a variety of materials, including sand, plaster, ceramic, and metal.

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5.1 Two forms of mold

(a) open mold (b) closed mold

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5.2 Casting process categories (according to type of mold used)

An expandable mold The mold in which the molten metal solidifies must be destroyed in order to remove the casting. These mold are made out of sand, plaster, and similar materials, whose form is maintained by using binders of various kind.

A permanent mold Can be used over and over to produce many castings. It is made of metals that can withstand the high temperature of the casting process

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6. Sand Casting Molds

Cope?Drag?A Flask?The parting line?A Pattern?A core?The gating system?A Downsprue?A runner?

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7. Heating

Heating furnaces is used to heat the metal to a molten temperature sufficient for casting.

The heat energy required is the sum of (1) heat to raise the temperature to the melting point, (2) heat a fusion to convert it from solid to liquid, and (3) heat to raise the molten metal to the desired temperature for pouring.

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7. Heating (continue) 11

8. Pouring The Molten Metal

After heating, the metal is ready for pouring. Introduction of molten metal into the mold, including its flow through the gating system and into the cavity, is a critical step in the casting process.

This step to be successful, the metal must flow into all region of the mold, including most important the main cavity, before solidifying.

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8. Pouring The Molten Metal (continue)

Factors affecting the pouring operation include: The pouring temperature the temperature of the

molten metal as it is introduced into the mold. Pouring rate volumetric rate which the molten

metal is poured into the mold. To slow the metal will chill and freeze before filling the cavity. To excessive turbulence.

Turbulence characterized by erratic variation in the magnitude and direction of the velocity throughout the fluid. The flow is agitated and irregular rather than smooth and streamline, as in laminar flow.

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9. Solidification and Cooling

Solidification involves the transformation of the molten back into the solid state.

Solidification pure metals

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9. Solidification and Cooling (continue)

Phase diagram for alloy system

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9. Solidification and Cooling (continue)

Eutectic Alloys

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10. Solidification Time

Total. Solidification Time time required for the casting to solidify after pouring.

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11. Shrinkage 18

12. Directional Solidification

Directional solidification is used to describe this aspect of the freezing process and the methods by which is controlled.

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13. Riser Design

Riser Design is used in a sand casting mold to feed liquid metal to the casting during freezing in order to compensate for solidification shrinkage

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Thank You

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