Dire Dawa university

School of Mechanical and Industrial Engineering

Manufacturing Engineering

A REPORT ON FUNDAMENTAL ASPECTS OF CASTING

Reported by:

1. Mohammed Mussa

2. Musse Ousman

Course Name: advanced casting

Summited to : Dr Simegn (PHD)

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 1. Contents
A Report on Fundamental of Metal Casting ................................... Error! Bookmark not defined.
1. Introduction .....................................................................................................................................................1
2. Fundamentals of metal castings ....................................................................................................................2
2.1 Heat Transfer Between the Metal and the Mold ..............................................................................2
2.1.1 Factors affecting heat transfer: ......................................................................................................2
2.2 Solidification of Pure Metal and Alloys................................................................................................3
2.2.1 pure metal ...............................................................................................................................................3
2.2.2 alloy ...........................................................................................................................................................4
2.3 Shrinkage in Cast Metals ...........................................................................................................................5
2.4 Progressive and Directional Solidification.........................................................................................6
3. Findings....................................................................................................................................................................7
4. Discussion ...............................................................................................................................................................8
5. Conclusion...............................................................................................................................................................8
6. References...............................................................................................................................................................9

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 1. Introduction

Casting is a manufacturing process in which a liquid material is usually poured into

a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify.

The solidified part is also known as a casting, which is ejected or broken out of the mold

to complete the process. Casting materials are usually metals and thermosetting materials

that cure after mixing two or more components together; examples

are epoxy, concrete, plaster and clay. Casting is most often used for making complex

shapes that would be otherwise difficult or uneconomical to make by other methods.

Heavy equipment like machine tool beds, ships' propellers, etc. can be cast easily in the

required size, rather than fabricating by joining several small pieces. This report detailed

information about four essential concepts in casting that are heat transfer between metal

and mould, solidification behavior of pure metals and alloys, shrinkage in cast metal, and

solidification techniques especially progressive and directional solidification. The

purpose of the report is to understand how these factors influence the quality, integrity,

and characteristics of cast metal products.

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 2. Fundamentals of metal castings

2.1 Heat Transfer Between the Metal and the Mold

. A typical temperature distribution at the mold liquid–metal interface. Heat from the

liquid metal is given off through the mold wall and to the surrounding air. The

temperature drops at the air–mold and mold–metal interfaces is caused by the presence of

boundary layers and imperfect contact at these interfaces. This process determines the

initial cooling rate and sets the stage for the solidification process. Factors such as mold

material, surface roughness, and thermal conductivity affect the efficiency of heat

transfer. The heat transfer during the complete cycle (from pouring, to solidification, and

to cooling to room temperature) is another important consideration in metal casting. Heat

flow at different locations in the system is a complex phenomenon and depends on

several factors relating to the material cast, the mold, and process parameters. For

instance, in casting thin sections, the metal flow rates must be high enough to avoid

premature chilling and solidification. On the other hand, the flow rate must not be so high

as to cause excessive turbulence—with its detrimental effects on the casting process.

Metals with high thermal conductivity (like copper) cool quickly, whereas sand molds

provide slower heat dissipation, allowing for more controlled solidification .

2.1.1 Factors affecting heat transfer:

Heat transfer, especially in processes involving molten metal and molds, is influenced by

several crucial factors. The thermal conductivity of the metal itself is paramount; a

higher conductivity allows for more rapid heat dissipation. Similarly, the mold

material's thermal conductivity plays a significant role, with materials like metal molds

facilitating more efficient heat transfer compared to less conductive options such as sand

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molds. Beyond material properties, the mold design also considerably impacts heat

transfer. Factors like the mold's surface area and overall geometry directly influence the

rate at which heat can be transferred from the molten metal. Finally, the initial

temperature difference between the molten metal and the mold is a fundamental driving

force, with a larger difference resulting in a more rapid rate of heat transfer.

2.2 Solidification of Pure Metal and Alloys

After molten metal is poured into a mold, a sequence of events takes place during

solidification and cooling of the metal to ambient temperature. These events greatly

influence the size, shape, uniformity, and chemical composition of the grains formed

throughout the casting, which, in turn, influence the overall properties of the casting. The

significant factors affecting these events are the type of metal cast, the thermal properties

of both the metal and the mold, the geometric relationship between volume and surface

area of the casting, and the shape of the mold. Pure metals solidify at a fixed temperature,

creating a uniform structure. In contrast, alloys solidify over a temperature range, often

forming dendritic structures with varying compositions due to solute redistribution. The

solidification path directly affects grain size, mechanical properties, and the presence of

casting defects. Understanding this behavior is critical for controlling the microstructure

of the final product. The significant factors affecting these events are the type of metal

cast, the thermal properties of both the metal and the mold, the geometric relationship

between volume and surface area of the casting, and the shape of the mold.

2.2.1 pure metal

Because a pure metal has a defined melting, or freezing, point, it solidifies at a constant

temperature, as shown in Fig. 1. Pure aluminum, for example, solidifies at 660°C, iron at

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1537°C, and tungsten at 3410°C. After the temperature of the molten metal drops to its

freezing point, its temperature remains constant while the latent heat of fusion is given

off. The solidification front (the solid– liquid interface) moves through the molten metal

from the mold walls in toward the center. The solidified metal, called the casting, is then

removed from the mold and allowed to cool to ambient temperature. As shown in Fig. 1b

and metals shrink while cooling and, generally, also shrink when they solidify .

FIGURE 1 (a) Temperature as a function of time for the solidification of pure metals;

note that freezing takes place at a constant temperature. (b) Density as a function of time.

2.2.2 alloy

Solidification in alloys starts when the temperature is below the liquidus, TL, and is

complete when it reaches the solidus, Ts (Fig. 2). inside this temperature range, the alloy

is in a mushy or pasty state, consisting of columnar dendrites. Dendrites have three-

dimensional arms and branches (secondary arms), which eventually interlock.

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The width of the mushy zone, where both liquid and solid phases are present, is an

important factor during solidification is described in terms of temperature difference and

is known as freezing zone .

Freezing zone = TS-TL ------------------------------------------------------------------- 1

Figure 2: alloy solidification and temperature distribution in the solidifying metal.

2.3 Shrinkage in Cast Metals

Because of the thermal expansion characteristics that metals have they tend to shrink

(contract) during solidification and while cooling to room temperature. Shrinkage, which

causes dimensional changes and sometimes warping and cracking, is the result of the

following three sequential events:

1. Contraction of the molten metal as it cools prior to its solidification

2. Contraction of the metal during phase change from liquid to solid

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3. Contraction of the solidified metal (the casting) as its temperature drops to ambient

temperature.

The largest shrinkage occurs during the phase change of the material from liquid to solid,

but this can be reduced or eliminated through the use of risers or pressure-feeding of

molten metal. The amount of contraction during the solidification of various metals is

shown in Table 1; note that some metals (such as gray cast iron) expand. The reason is

that graphite has a relatively high specific volume, and when it precipitates as graphite

flakes during solidification of the gray cast iron, it causes a net expansion of the metal.

Shrinkage.

Failure to manage shrinkage can result in defects like internal voids or surface

depressions. The use of risers and proper mould design helps mitigate these issues .

2.4 Progressive and Directional Solidification

If the feeder can be placed on the thickest section of the casting, with progressively

thinner sections extending away, then the condition of progressive solidification towards

the feeder can usually be achieved in other word solidification occur when solidification

starts at the mould walls and moves inward which may lead to shrinkage if not properly

controlled. Directional solidification is a technique where the solidification front moves

in a controlled direction, typically toward a riser that supplies molten metal to

compensate for shrinkage. It ensures a sound casting, especially for critical parts

requiring high structural integrity. The unidirectional solidification of castings has a long

history, promoted initially by the desire to obtain high soundness; the high temperature

gradient shortening the pasty zone so that feeding could occur to the roots of the

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dendrites with greater efficiency. Directional solidification (DS) is mostly usedto imply

unidirectional solidification. It has been used for permanent magnet manufacture, but its

main use has been for turbine blades for jet engines. In practice, DS has nearly always

been carried out vertically in an upward direction. It was not suspected that this particular

mode of freezing would yield an additional important effect; a significant reduction in the

bifilm population. This occurs partly (i) by the vertically directed freezing allowing

bifilms to float upward, away from the freezing front, and (ii) because of the unusually

long time available for this flotation because of the relatively slow rate of advance of the

front during DS, and (iii) any residual bifilms will have the best chance to be pushed

ahead of the advancing solidification front, thereby keeping the solid relatively free from

serious defects.

3. Findings

- Heat transfer rates vary significantly with mold materials and affect solidification speed.

- Pure metals offer predictable solidification but alloys require careful monitoring due to

segregation.

- Shrinkage is inevitable, but proper design (risers, chills) can prevent defects.

- Directional solidification yields better quality castings by guiding defect formation to

non-critical areas.

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 4. Discussion

The report emphasizes the interconnectedness of thermal and physical phenomena in

casting. The way heat is transferred and how metals solidify directly influences casting

integrity. For alloys, controlling the solidification range is crucial to avoid chemical

inhomogeneity. Moreover, shrinkage management is essential to prevent structural

failures. The adoption of directional solidification techniques reflects advanced control in

modern casting practices, essential for producing reliable and high-performance parts.

5. Conclusion

This report has explored four key elements of casting: heat transfer, solidification,

shrinkage, and solidification techniques. Understanding these aspects allows engineers to

optimize casting conditions for better product quality. Future work may focus on

computational modelling of heat flow and solidification for even more precise control,

particularly in complex alloy systems.

Recommendations:

1. Use simulations to predict solidification paths and shrinkage zones.

2. Select mould materials based on desired cooling rates.

3. Implement directional solidification where high-quality castings are needed.

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 6. References

1. Kalpakjian, S., & Schmid, S. R. (2014). *Manufacturing Engineering and

Technology*. 7th ed. Pearson Education.

2. ASM International (1990). *ASM Handbook, Volume 15: Casting*. ASM

International.

3. Matiskova, D., Gasper, R., & Mura, J. (2013). Thermal Factors of Die Casting and

Their Impact on the Service Life of Moulds and the Quality of Castings. Acta

Technica Jaurinensis, 6(1), 3-10

4. Campbell, J. (2015). *Complete Casting Handbook: Metal Casting Processes,

Metallurgy, Techniques and Design*. 2nd ed. Butterworth-Heinemann.

5. Ravi, B. (2005). *Metal Casting: Computer-Aided Design and Analysis*. Prentice-

Hall of India.

6. Flemings, M. C. (1974). *Solidification Processing*. McGraw-Hill.

7. Degarmo, E. P., Black, J. T., & Kohser, R. A. (2011). *Materials and Processes in

Manufacturing*. 11th ed. Wiley.

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