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NED UNIVERSITY OF ENGINEERING AND TECHNOLOGY

DEPARTMENT: Materials Engineering

COURSE TITLE: MM-203: Melting and Casting of Materials

FALL SEMESTER: 2012

TEACHER: Engr. Humair Ahmed / Engr. Faaz Butt.

Text Book;

1) P L Jain, PRINCIPLES OF FOUNDRY TECHNOLOGY 2009; English: 5th ed.

References;

1. C. W. Ammen, METALCASTING, 1999.

2. ASM HandBook - Vol 15 - Casting (2002s).

2. Peter, Beeley FOUNDRY TECHNOLOGY, Butterworth-Heinemann; 2nd ed., 2006

3. Chakrabarti, A K, CASTING TECHNOLOGY AND CAST ALLOYS, 2005.

5. Heine, R.W., et.al., PRINCIPLES OF METAL CASTING, 3rd. ed., Tata McGraw-Hill

Publ., 1979.

Evaluation;

1. Popup Quizzes (approx. 5): 5%.

2. Test: 10%.3. Assignment: 10%.

4. Attendance: 5%

4. Final examination: 70%

SYNOPSIS OF COURSE:

This course is one of the most important and interesting subject for Materials

Engineering students.

It is advancement from the previously taught subject, the manufacturing processes for

materials (MM-206).

The subject comprises a more emphasis on the manufacturing techniques by castingprocess.

It covers bigger spectrum for manufacture products by the casting techniques with

require attributes specify for certain purpose such as intricacy, features detail,

soundness and others.

REMEMBER!!!!

The true art of memory is the art of attention

Samuel Johnson

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MELTINGANDC

ASTINGOFMATERIA

LS

MELTING

To

bechangedfrom

asolidtoa

liquid

state

especiallyb

y

the

applicationofheat.

Thestateofbeingmelted.

Theprocessofbecomingmelted

CASTING

Castingisa

manufacturingprocess

whereasolidismelted,heatedto

propertem

perature

and

is

then

pouredinto

acavityormold,which

containsit

in

thepropershape

during

solidification.

Thus,in

a

single

step,simple

orcomplex

shapescanb

emadefromanymetal

thatcanbem

elted.

Materials

Thetangiblesubsta

ncethatgoes

intothemakeupofaphysical

object.

EngineeringMaterials:Materials

ofengineeringapplications.

Classificationof

materials,

nextslide

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Everything

isMaterial!!

MetallicMaterials

Metallic:

Iron

Copper

Aluminum

Magnesium

Nickel

Titanium

Lead

Tin

Zinc

Alloysofthesemetals:

Steel(Febased)

Brass(Cu+Zinc)

Bronze(Cu+Tin

)

Theypossessthemetallicpropertiesof:

Luster

Highthermalconductivity

Relativelyductile

Some

have

good

magnetic

properties

T

herearetwofamiliesofmetallicmaterialsFERROUSAND

NONFERROUS.

Nonmeta

llicMaterials

Nonmetallic:

Wood

Brick

Concrete

Glass

Rubber

Plastic

Theirpropertiesvarywidely

Generallytheyten

dtobe:

Lessductile

Weaker

Lessdensethanm

etals

Havepoorelectricalandthermalproperties

N

onmetallicMaterialsared

eveloping

Advancedceramics

Compositematerials

Engineeredplastics

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M

etalliccastings

N

on-metalliccastings

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A

dvantagesofthe

MetallicandNon

metalliccastingp

rocess

C

ertainadvantagesareinhe

rentinthemetalcastingp

rocess.

Theseoftenformthebasisforchoosingcastingover

o

thershapingprocessessuc

hasmachining,forging,w

elding,s

tamping,rolling,extruding,etc.Someofthe

reasons

forthesuccessofthecastingprocessare:

Themostintrica

teofshapes,

bothexternalandinternal,maybecast.

Asaresult,manyother

operations,suchasmachining,forging,andwelding,canbeminimized

oreliminated.

Constructionmay

besimplified.Objectsm

aybecastinasinglepie

cewhichwouldotherwise

require

assemblyofseveralpiecesifmadebyothermethods.

Metalcastingisa

processhighlyadaptabletotherequirementsofmassproduction.Largenumbersof

agivencastingm

aybeproducedveryrap

idly.

Forexample,inthe

automotiveindustryhundredsof

thousandsofcastengineblocksandtransmissioncasesareproducedea

chyear.

Extremelylarge,heavymetalobjectsmaybecastwhentheywouldbedifficultoreconomically

impossibletoproduceotherwise.Largepum

phousing,valves,andhydroelectricplantpartsweighingup

to200tonsillustratethisadvantageoftheca

stingprocess.

Someengineerin

gpropertiesareobtaine

dmorefavorablyincastm

etal.

Adecidedeconomicadvantagemayexis

tasaresultofanyoneoracombinationofpointsmentioned

above.

SurpriseQuiz:

1)DefineMeltingan

dCastingPracticeintermsofitsimportance.(

Max:

5lines)

2)Writeanythreesa

fetyissuesrelatedtotheM

eltingandcastingofmaterials.

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CASTING OF MATERIALS

The metal casting industry plays a key role in all the majorsectors of our economy.

There are castings in locomotives, cars trucks, aircraft, office buildings, factories,

schools, and homes.

Metal Castingis one of the oldest materials shaping methods known.

Casting means pouring molten metal into a mold with a cavity of the shape to bemade, and allowing it to solidify.

When solidified, the desired metal object is taken out from the mold either by breaking

the mold or taking the mold apart. The solidified object is called the casting.

By this process, intricate parts can be given strength and rigidity frequently not

obtainable by any other manufacturing process.

The mold, into which the metal is poured, is made of some heat resisting material.

Sand is most often used as it resists the high temperature of the molten metal.

Permanent molds of metal can also be used to cast products.

Advantages

The metal casting process is extensively used in manufacturing because of its many

advantages.

1. Molten material can flow into very small sections so that intricate shapes can be made by

this process. As a result, many other operations, such as machining, forging, and welding,

can be minimized or eliminated.

2. It is possible to cast practically any material that is ferrous or non-ferrous.

3. As the metal can be placed exactly where it is required, large saving in weight can be

achieved.

4. The necessary tools required for casting molds are very simple and inexpensive. As a

result, for production of a small lot, it is the ideal process.

5. There are certain parts made from metals and alloys that can only be processed this way.

6. Size and weight of the product is not a limitation for the casting process.

Limitations

1. Dimensional accuracy and surface finish of the castings made by sand casting processes

are a limitation to this technique. Many new casting processes have been developed which

can take into consideration the aspects of dimensional accuracy and surface finish. Some of

these processes are die casting process, investment casting process, vacuum-sealed moldingprocess, and shell molding process.

2. The metal casting process is a labor intensive process

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METAL CASTINGS

Metal castings form integral components of devices that perform useful functions for human

beings:

The cast component has a shape, size, chemical composition and metallurgical

microstructure which is determined by engineering decisions arrived at by:

A. Design Engineers (Mechanical Engineers)

B. Pattern Makers (Skilled craftsman, CAD)

C. Casting Engineers (Materials/Metallurgical Engineers)

D. Manufacturing Engineers (Mechanical, Materials/Metallurgical Engineers)

It should be noted that the casting may only be a small part of the useful device

(usually in more sophisticated devices like an automobile where there may be

hundreds of components), or it may be the entire device (simple device like a frying

pan).

Metal Casting Process

The metal casting process is the simplest, most direct route to a near net shape

product, and often the least expensive.

This process in its fundamental form requires a mold cavity of the desired shape and

molten metal to pour into the mold cavity.

Humans beings have been producing castings for thousands of years, most often

pouring molten metal into molds made of sand.

This is schematically shown below, a figure defining the basic components of a mold

cavity (cope, drag, parting line, riser, sprue, pouring basin, etc)

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Engineering skills are used to help design a system which will allow the metal caster

to produce asound (pore free) casting, free from defects (sand inclusions, slag,

cracks, etc.), with the correct dimensionsand combination of mechanical properties to

satisfy the designers requirements for the intended application.

Producing a good casting requires a design effort to:

1. Create agating system (pouring basin, sprue, runner)to bring molten metal into the

mold cavity free from entrapped slag, sand or gases.

2. Provide a riser which feeds liquid metalinto the casting cavity as the liquid is cooling and

solidifying (all liquid metals will shrink as they cool and most liquid metals will shrink as

they solidify). The riser may have to provide up to 5 - 7% by volume for the casting as it

solidifies.

3. Control heat flow, out of the casting so that the last liquid to solidify is in the riser.

4. Control the rate of heat flowso as to control the nature of the solidified product.

Modern industrial castings are produced by a wide variety of processes, processes which are

broadly defined in terms of:

I. The type of mold material(sand, permanent, etc.);

II. The mannerin which the molten metal is introduced into the cavity (gravity,

pressure, vacuum);

III.

The state of the metal(percent which is liquid);IV. The state of the mold cavityitself (air, vacuum, solid, gas).

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EXPENDABLE MOLD CASTING

Expendable mold casting is a process that refers to temporary, non-reusable molds that haveto be broken to remove the materials cast. Expendable casting uses a variety of materials forthe mold - plaster, concrete, resins, and wax.

1) Sand casting

Sand casting is one of the most popular and simplest types of casting that has been used for

centuries. Sand casting allows for smaller batches to be made compared to permanent mold

casting and at a very reasonable cost. Not only does this method allow manufacturers tocreate products at a low cost, but there are other benefits to sand casting, such as very small

size operations. From castings that fit in the palm of your hand to train beds (one casting can

create the entire bed for one rail car), it can all be done with sand casting. Sand casting alsoallows most metals to be cast depending on the type of sand used for the molds.

The sand is bonded together using clays, chemical binders, or polymerized oils (such as

motor oil). Sand can be recycled many times in most operations and requires littlemaintenance.

2) Shell molding

Shell molding is similar to sand casting, but the molding

cavity is formed by a hardened "shell" of sand instead of

flask filled with sand. The sand is finer than sand casting

sand and is mixed with a resin so that it can be heated by

the pattern and harden into a shell around the pattern.

Because of the resin it gives a much finer surface finish.

The process is easily automated and more precise thansand casting. This process is ideal for complex itemsthat are small to medium sized.

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3) Investment casting

Investment casting (known as lost-wax casting in art) is a process that has been practiced for

thousands of years, with the lost-wax process being one of the oldest known metal forming

techniques. From 5000 years ago, when beeswax formed the pattern, to todays high

technology waxes, refractory materials and specialist alloys, the castings ensure high-quality

components are produced with the key benefits of accuracy, repeatability, versatility and

integrity.

Investment casting derives its name

from the fact that the pattern is

invested, or surrounded, with a

refractory material. The wax patterns

require extreme care for they are not

strong enough to withstand forces

encountered during the mold making.

One advantage of investment casting isthat the wax can be reused.

The process is suitable for repeatable

production of net shape componentsfrom a variety of different metals and

high performance alloys. Compared to

other casting processes such as die casting or sand casting, it can be an expensive process,

however the components that can be produced using investment casting can incorporate

intricate contours, and in most cases the components are cast near net shape, so requiringlittle or no rework once cast.

4) Evaporative-pattern casting

This is a class of casting processes that use pattern materials that evaporate during the pour,

which means there is no need to remove the pattern material from the mold before casting.

The two main processes are lost-foam casting and full-mold casting.

i. Lost-foam casting

Lost-foam casting is a type of evaporative-pattern casting process that is similar to

investment casting except foam is used for the pattern instead of wax. This process takes

advantage of the low boiling point of foam to simplify the investment casting process by

removing the need to melt the wax out of the mold.

ii. Full-mold casting

Full-mold casting is an evaporative-pattern casting process which is a combination of sand

casting and lost-foam casting. It uses a expanded polystyrene foam pattern which is then

surrounded by sand, much like sand casting. The metal is then poured directly into the mold,which vaporizes the foam upon contact.

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NON-EXPENDABLE CASTING TECHNIQUES

Non-expendable casting involves the use of permanent or long-lasting molds which do notneed to be broken in order to remove the cast material once it has set or cooled.

1) Permanent mold casting

Permanent mold casting uses metal as a mold and requires a set-up time of weeks.Typically, cast iron or Meehanite (a dense cast iron) is used as the mold material and

the cores are made from metal or sand.

Cavity surfaces are coated with a thin layer of

heat resistant material such as clay or sodium

silicate.

The molds are pre-heated up to 200C before

the metal is poured into the cavity.

When cooling the mold, care has to be taken to

ensure proper thermal balance, by using

external water cooling or appropriate radiationtechniques

The process is highly automated, as the only

necessary input is the coating applied regularly.

Typically, permanent mold casting is used in forming iron, aluminum, magnesium,

and copper based alloys.

Typical parts include gears, splines, wheels, gear housings, pipefittings, fuel injection

housings, and automotive engine pistons.

2)

Die Casting Die-casting is similar to permanent mold

casting except that the metal is injected into

the mold under high pressures. This results in

a more uniform part, generally good surface

finish and good dimensional accuracy.

For many parts, post-machining can be totally

eliminated, or very light machining may berequired to bring dimensions to size.

Die casting molds, called dies, tend to beexpensive as they are made from hardened

steel-also the cycle time for building these

tend to be long.

The die casting method is especially suited for

applications where many small to medium sized parts are needed with good detail, a

fine surface quality and dimensional consistency.

Most die castings are made from nonferrous metals, specifically zinc, copper, and

aluminum based alloys.Stronger and harder metals such as iron and steel cannot be

die-cast.

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3) Centrifugal casting

Centrifugal casting is both gravity- and

pressure-independent.

A permanent mold is rotated about its axis at

high speeds (300 to 3000rpm) as the molten

metal is poured.

The molten metal is centrifugally thrown

towards the inside mold wall, where it solidifies

after cooling.

The casting is usually a fine grain casting with

a very fine-grained outer diameter, which is

resistant to atmospheric corrosion, a typical

situation with pipes.

The inside diameter has more impurities and inclusions, which can be machined away.

Typical materials that can be cast with this process are iron, steel, stainless steels, and

alloys of aluminum, copper and nickel.

Continuous casting

In continuous casting, molten metal is pouredinto an open-ended, water-cooled copper

mold, which allows a 'skin' of solid metal to

form over the still-liquid centre.

The strand, as it is now called, is withdrawn

from the mold and passed into a chamber ofrollers and water sprays; the rollers support

the thin skin of the strand while the sprays

remove heat from the strand, gradually

solidifying the strand from the outside in.

After solidification, predetermined lengths of

the strand are cut off by either mechanical

shears or travelling oxyacetylene torches andtransferred to further forming processes, or to

a stockpile.

Cast sizes are referred to as strips (which are a few

millimeters thick by about five meter wide), billets

(which can from 90 to 160mm square), and slabs

(which are 1.25m wide by 230mm thick).

Continuous casting represents vast savings in time,labor, energy, and capital. By casting the steel

directly into semifinished shapes, the following

steps are eliminated: ingot teeming, stripping, and

transfer; soaking pits; and primary rolling.

Continuous casting also increases yield and product quality. Metals such as steel,copper and aluminium are continuously cast, with steel being the metal with thegreatest tonnages cast using this method.