Metal Casting Processesstaff.psu.edu.eg/sites/default/files/habdelhafez/files/metal-casting_processes-2.pdfInvestment Casting Procedure: 1. Wax Injection: Wax replicas (patterns of

Metal –Casting Processes

Source : Manufacturing Processes for Engineering Materials,5rd Edition., S. Kalpakjian and S. Schmid, 2008 , Additional references in the last slide

Casting

Expendable mold

Sand casting

Shell casting

Investment casting

Lost foam casting

Multiple –use mold

Die casting

Permanent mold casting


Outline

Why study metal casting ?

Benefits of Metal Casting

History of Metal Casting

Overview of Metal Casting Science

Solidification of Metals

Cast Structures: Pure Metals

Cast Structures: Alloys

Effect of Cooling Rate

Structure Property Relationships

Why Study Metal Casting ?

4

Over 75 million metric tons of cast components are produced annually

worldwide

What is Metal Casting ?

5

Benefits of Metal Casting

Near “Net-Shape” manufacturing

Does not waste material like machining

Can produce intricate shapes

Can produce hollow structures

Can produce internal features

It is very cost effective as compared to

other processes

6

History of Metal Casting

One of the oldest sciences

Started around 4000 BC

Today has modern methods like

investment casting, die casting etc.

It is used to produce heavy items like

engine blocks as well as light items like

jewelry

Relevance to Saudi Arabia - I

Relevance to Saudi Arabia - II

9

Science of Metal Casting

The following sciences are involved in

Metal Casting:

1. Flow of Molten Material into the Mold

Cavity

2. Solidification of Molten Metal

3. Heat transfer During Solidification

4. Mold and Molten Material Study

10

In this lecture we will primarily focus on Solidification

Cast Structures

Cast structure developed during solidification of

metals and alloys depends on:

1. composition of the particular alloy

2. the rate of heat transfer

3. flow of the liquid metal during the casting

process

Solidification of Metals: Pure Metals - I

12

Solidification of Metals: Pure Metals - II

13

Pure metals have defined melting points and

solidification takes place at a constant temperature.

Alloys solidify over a range of temperatures.

Q1. How does SOLIDIFICATION effect the Cast

Structure ?

Q2. How does SOLIDIFICATION effect

Mechanical Properties ?

14

Let us see in the following Slides

Cast Structures : Pure Metals

Solidification Process by Dendrite Growth (movie)

Grain Structure of an Ingot: Aluminum Alloy

16

1. Solidification starts at the edges

2. Grain growth takes place from

the edges towards the center

3. Note Columnar grain structure

5. Center Solidifies at last :

Note Porosity

4. Note Equiaxed grains near

center

Cast Structure of Pure Metals & Alloys

17

(a) Pure Metals

Columnar grain structure:

Weak Mechanical

Properties


18

(a) Pure Metals (b) Solid Solution Alloys


Weak Mechanical

Properties

Equiaxed

grains:

Better

Mechanical

Properties


19


(c) Heterogeneous

nucleation of grains :

Alloys


Weak Mechanical

Properties

Equiaxed

grains:

Better

Mechanical

Properties

Q: Why do smaller grains have better

Mechanical Properties ?

Hall – Petch Relationship

Y = Yi + k/ d(1/2)

Where Y = Improved Yield Strength

Yi = Basic Yield Stress

d = grain size (diameter)

k = dislocation constant

20

So we see smaller grain sizes lead to Higher

Yield Strength

Mid lecture Summary

The aim is to control mechanical

properties throughout a production

process

In the case of castings the aim is to

end up with a small grain size with

better mechanical properties

In castings the grain size is primarily

affected by 2 things:

1. Alloying Elements

2. Solidification Rate 21

Next Let us try to understand how alloying

elements affect solidification ?

Affect of Alloying Element on Solidification

23

Alloy

Pure Metals when cooled , go

directly from Liquid State into a

Solid State

Alloys when cooled , do not go

directly from Liquid to Solid

State,

But pass through a Liquid +

Solid State (Mushy Zone)

Affect of Mold Wall on Solidifying Metal

24

Cold

Mold

Wall

1. First Solidification will take

place immediately next to

the mold wall

6. The center of

the mold will be

the last to

solidify

Hot Molten Liquid Metal in

Mold

2. Second , solidification will

advance from mold wall toward

the inside of the mold.

3. This advance will take place in

the shape of dendrite growth.

4. Dendrites will grow like trees

from the mold wall into the liquid

metal.

5. This growth will take place from

all sides of the mold.

Solidification Rate / Cooling Rate

In Practice Property Structure 0K/ Sec

Sand Molds Poor Large

Dendrites

102 1. Slow

Cooling Rate

Metal Molds Better Small

dendrites*

104 2. High

Cooling Rate

Special

Techniques

Best Amorphous

(no crystals)

106 - 108 3. Ultra High

Cooling Rate

Higher cooling rates also give rise to smaller grains and hence better Yield Strength

( remember Hall Petch Relationship)

STRUCTURE PROPERTY RELATIONSHIPS

26

Structure-property relationships

Columnar dendritic Equiaxed dendritic Equiaxed nondendritic

Recall earlier slide :


28


(c) Heterogeneous


Alloys


Weak Mechanical

Properties

Equiaxed

grains:

Better

Mechanical

Properties


29


(c) Heterogeneous


Alloys

So the Question is :

How do we make this

into this ?

Creating equiaxed grain structures

By adding a grain nucleating agent in the

melt we can have grains nucleating at

multiple sites

Hence resulting in an overall smaller grain

structure

TiBor TiB is a typical grain nucleating agent for aluminum

alloys

Without Tibor: Larger grain size With Tibor: Smaller grain size

Summary - I

Metal castings are used for “Net-

Shape” manufacturing

Solidification of the melt is responsible

for the resulting microstructure

The microstructure is responsible for

Mechanical Properties of the cast part

We can control the microstructure

32

Summary - II

Faster Cooling Rates give smaller grain

structures

Smaller grain structures give higher

Yield Strength (Hall Petch Relationship)

Smaller grain structure can also be

obtained by adding grain size reducers

in the melt

33

34

Metals processed by casting

Sand casting – 60%

Permanent mold casting – 11%

Die casting – 9%

Investment casting – 7%

Centrifugal casting – 7%

Shell mold casting – 6%


Types of Parts Made

Engine blocks

Pipes

Jewelry


Mold Features

The following is a gravity casting system.

2 principles of fluid flow are relevant to gating design:

Bernoulli’s theorem and the law of mass continuity.


Components of Casting

Path: Sprue -> Well -> Runner -> Mold cavity

Riser: Compensate volume loss due to shrinkage

Location of riser?

Core: Make holes

Core print

Draft: Prevent collapse

of sand



Ferrous casting alloys Cast irons represent the largest amount of all metals

cast and can cast into complex shapes.

Types of irons:

Gray cast iron

Ductile iron (nodular iron)

White cast iron

Malleable iron

Compacted-graphite iron

Cast steels

Cast stainless steels


Nonferrous casting alloys

Types of alloys:

Aluminum-based alloys

Magnesium-based alloys

Copper-based alloys

Zinc-based alloys

High-temperature alloys


Expendable-Mold

Permanent-Pattern Casting Processes


1. Sand Casting

Types of sand molds

3 types: green-sand, cold-box, and no-bake

molds.

Green molding sand is mixture of sand, clay,

and water and is inexpensive.

In skin-dried method, castings has high

strength, better accuracy and surface finish.

In no-bake mold process, a synthetic liquid

resin is mixed with the sand and hardened in

room temperature.


Sand Casting




2.Shell-mold casting Can produce castings with close

dimensional tolerances

Good surface finish

Low cost.


2.Shell-mold casting

Shell Moulding

Features:

- Metallic pattern is used.

- Moulding material: Fine sand + Thermosetting resin

(phenol-formaldehyde)

(5 kg of phenol-formaldehyde in 100 kg of sand)

- Heating arrangement for the pattern (>180 ̊ C)

Casting Processes

Shell Moulding

Advantages:

- Complex parts can be produced .

- Dimensional accuracy is high.

- Surface finish is good (1.25μm to 3.75μm ).

- Moulds are lightweight and may be stored for extended periods of

time.

- Less foundry space required.

- Metal yields are relatively high.

- Sand: Metal ratio are relatively low.

- Incurs lower fettling costs than conv. Sand casting.

Casting Processes

Shell Moulding

disadvantages:

- Not economical for small scale production.

- Resin costs are comparatively high.

- Suitable only for small castings, maximum weight of the component is

10 kg.

Applications:

- Automotive rocker arms and valves.

- Cam shafts, Bushings, Valve bodies, spacers, Brackets. Bearing caps

etc.

3. Ceramic Mold Manufacture

FIGURE 5.18 Sequence of operations in making a ceramic mold.


Description: Green Sand Casting Capabilities

Horacio Elizondo Author

April 2003 Date

Alting,Leo. “Manufacturing Processes Reference Guide.” 1994 Reference

Shape Material Conserve Material Consolidation Function – Sub function


Expendable-Mold,

Expendable-Pattern Casting Processes


1. Expendable-pattern casting (lost foam) Evaporative Pattern Casting

FIGURE 5.20 Schematic illustration of the expendable-pattern casting process, also known as

lost-foam or evaporative-pattern casting.


2. Investment Casting (lost-wax process)

Source: Schematic illustration of investment casting (lost wax process). Castings by this

method can be made with very fine detail and from a variety of metals. Source: Steel

Founders' Society of America. Source : Manufacturing Processes for Engineering Materials,5rd Edition., S. Kalpakjian and S. Schmid, 2008 , Additional references in the last slide

Casting Processes

Investment Casting Procedure:

1. Wax Injection: Wax replicas (patterns of the desired castings are

produced by injection moulding.

2. Assembly: The patterns are attached to a central wax stick, called

a sprue , to form a casting cluster or assembly.

3. Shell Building Coating with Ethyl silicate + Fine silica sand

slurry.

4. Dewax: Once the ceramic shell is dry, the wax is melted out,

creating a negative impression of the assembly within the shell.

Casting Processes

Investment Casting Procedure:

5. Conventional casting: In the conventional process, the shell is

filled with molten metal by gravity pouring.

6. Knockout: When the metal has cooled and solidified, the ceramic

shell is broken off by vibration or water blasting.

Description: Investment Casting Capabilities


April 2003 Date




Investment Casting


Casting Processes

Advantages of Investment Casting :

1. Excellent surface finish

2. Produces very fine details (Jewellery castings etc.)

3. Very thin sections can be made ( as thin as 0.75 mm).

4. Close dimensional tolerances (0.08 – 0.1 mm).

5. Complex shapes can be made.

6. No or negligible finishing operations

7. Castings are free from usual defects.

Casting Processes

Disadvantages of Investment Casting :

1. Production of wax patterns make the process costly.

2. Bigger castings cannot be made (Generally about 0.5

kg).

3. Process is relatively slow.

4. Incorporating the cores is difficult.

Casting Processes

Applications of Investment Casting :

- Jewellery castings

- Art castings

- Difficult to machine alloys

- Milling cutters and other tools

- Impellers and other pump components

- Jet aircraft nozzles

- Parts of sewing machines, locks and rifles

Permanent-Mold Casting Processes


Casting Processes

Permanent mould process

Drawback of sand mould process:

A mould need to be prepared for each of the casting produced.

Specialty of permanent mold process:

A METALLIC MOULD is used in the place of sand mould with which large

number of castings are made. The metallic mould is known as die.

Casting Processes

Permanent mould process

Also known as DIE CASTING:

Mould material: Metal or alloy

Types of Die Casting process:

1.Gravity Die Casting

2. Pressure Die Casting:

a. Cold chamber pressure die casting.

b. Hot chamber pressure die casting.

Description: Permanent Mold Casting Capabilities


April 2003 Date




Pressure & Hot-Chamber Die Casting

The pressure casting process, utilizing graphite molds for the production of steel

railroad wheels. Source: Griffin Wheel Division of Amsted Industries Incorporated.

Schematic illustration of the hot-chamber die-

casting process.


Description: Hot Chamber Die Casting Capabilities


April 2003 Date




Cold-Chamber Die Casting

FIGURE 5.25 Schematic illustration of the cold-chamber die-casting process. These machines are large

compared to the size of the casting, because high forces are required to keep the two halves of the die closed

under pressure. Source : Manufacturing Processes for Engineering Materials,5rd Edition., S. Kalpakjian and S. Schmid, 2008 , Additional references in the last slide


Die Casting


Casting Processes

Advantages of die casting:

1. Closer dimensional accuracy.

2. Good surface finish on castings.

3. Useful for mass production (One set of die can produce about 10,000 castings).

4. Less floor space is required.

5. Cycle of operation requires less time.

6. Porosity can be avoided.

7. Faster rate of production.

8. Semi skilled workers can do the job.

9. Less defects compared to sand castings.

10. Casting surface free from sand.

Casting Processes

Limitations of die casting:

1. Cost of the die is high.

2. Not suitable for heavy castings.

3. Suitable only for non-ferrous castings.

4. Not suitable for small scale production.

Casting Processes

Applications of die casting:

1. Carburetor bodies.

2. Hydraulic brake cylinders.

3. Connecting rods and automotive pistons.

4. Oil pump bodies.

5. Aircraft components.

Type Composition (%) Use

C Cr Mo W V Co Ni

H11 0.35 5.0 1.5 - 0.5 - - Zn casting

dies

H12 0.35 5.0 1.5 1.5 0.4 - - Al casting

dies H13 0.35 5.0 1.5 - 1.0 - -

H19 0.40 4.25 - 4.25 2.0 4.25 - Brass &

Bronze

casting dies H20 0.35 2.0 - 9.0 - - -

H21 0.35 3.5 - 9.0 - - -

Die Materials:

Casting Processes

Continuous Casting :

- Used to cast long ingots, square billets etc.

Types of continuous casting

- Vertical continuous casting

- Horizontal continues casting

- Continuous casting in traveling mould

Continuous-Casting

(a) The continuous-casting process for steel. Note

that the platform is about 20 m (65 ft) above

ground level. Source: American Foundrymen's

Society.

(b) (b) Continuous strip casting of nonferrous metal

strip. Source: Courtesy of Hazelett Strip-Casting

Corp.


Continuous Casting in traveling mold :

Advantages of Continuous Casting :

- 100 % casting yield.

- Cheaper to produce ingots (compared to rolling).

- Better surface finish.

- Grain structure can be regulated

- Process is automatic – requires less labor

Casting Processes

Centrifugal casting:

- Developed by A. G. Eckhardt in England during 1809.

- Utilizes the centrifugal forces caused by rotation to distribute the

molten metal in to the mould cavities.

- First used in the 1800’s

- Three types of centrifugal casting

- True centrifugal casting

- Semi centrifugal casting

- Centrifuging

Applications of Continuous Casting :

- Long Billets of any cross section can be obtained

(Round, square, hexagonal, gear toothed.

- Solid and hollow ingots can be made.

- Bushings and pump gears.

- Production of copper bar (wire)

Centrifugal Casting

The centrifugal casting process. Pipes, cylinder liners, and similarly shaped

hollow parts can be cast by this process.


Centrifugal casting:



Semicentrifugal Casting

(a) Schematic illustration of the semicentrifugal casting process. Wheels with spokes can be cast by this

process.

(b) Schematic illustration of casting by centrifuging. The molds are placed at the periphery of the machine, and

the molten metal is forced into the molds by centrifugal forces.


Casting Processes

True Centrifugal casting Procedure:

1. Applying ceramic slurry to the mould wall, drying and baking.

2. Rotation of the mould at a predetermined speed (300 to 3000

rpm).

3. Pouring a molten metal directly into the mould (no gating system

is employed).

4. The mould is stopped after the casting has solidified.

5. Extraction of the casting from the mould.

Casting Processes

Centrifugal casting Advantages

1. Formation of hollow cavities in cylinders without cores.

2. Non-metallic and slag inclusions and gas bubbles are forced to the

inner surface of the casting by the centrifugal force.

3. No gating system, hence casting yield is high (100% in many times).

4. Fettling costs are reduced. Cost of production is less.

5. Casting free of gas and shrinkage cavities and porosity.

6. Fine outside details (castings) can be successfully cast.

7. Easy to inspect the castings (defects occur on the surface).

Casting Processes

Centrifugal casting disadvantages

1. More segregation of alloy component during pouring

under the force of rotation.

2. Suitable only for axial symmetrical components.

3. Skilled workers are required for operation.

4. Inaccurate internal diameter.

Casting Processes

Applications of centrifugal casting

1. Cast iron pipes.

2. Liners for I.C. Engines.

3. Bushings.

4. Wheels.

5. Pulleys.

6. Bi-metal steel-bronze bearings.

7. Other parts possessing axial symmetry.


Properties of Die-Casting Alloys

TABLE 5.6 Properties and typical applications of common die-casting alloys.


Rotor Microstructure

Microstructure of a rotor that has been investment cast (top) and

conventionally cast (bottom). Source: Advanced Materials and Processes.


Fluid Flow and Heat Transfer

Bernoulli’s theorem

Based on

- principle of conservation of energy

- frictional losses in a fluid system

Conservation of energy requires that,

Constant 2

2

g

v

g

ph

h = elevation

p = pressure at elevation

v = velocity of the liquid

ρ = density of the fluid

fg

v

g

ph

g

v

g

ph

2

2

2

222

2

111



- Fluid flow

Mass continuity

States that for an incompressible liquid the rate

of flow is constant.

Subscripts 1 and 2 pertain to two different

locations in the system.

2211 vAvAQ Q = volumetric rate of flow

A = cross-sectional area of the liquid stream




- Fluid flow

Sprue profile

Relationship between height and cross-sectional area

at any point in the sprue is given by

Velocity of the molten metal leaving the gate is

When liquid level reached height x, gate velocity is

1

2

2

1

h

h

A

A

ghcv 2

xhgcv 2



- Fluid flow

Flow characteristics Reynold’s Number

Ratio of momentum (inertia) to viscosity

Fluid flow in gating systems is turbulence, as opposed

to laminar flow. (Which flow is preferred?)

Reynolds number, Re, is used to characterize this

aspect of fluid flow.

Higher the Re, greater the tendency for turbulent flow.

vDRe


D = diameter of the channel

ρ = density

n = viscosity of the liquid.


Critical Reynold’s Number

• Re ~ 2,000

– Laminar to turbulent transition

– Eddies begin to form

• Re > 20,000

– very turbulent


How fast would a stream of honey 1 in.

in diameter need to be turbulent?

Density (ρ) = 1.43 g/cm3 (at 20oC)

Viscosity () = 189 poise (at 20.6oC) {1poise=1kg*m^-1*s^-1}

vDRe

9.18

1430254.0Re

vturbulent flow transition

Re ~ 2,000

Re = 2,000 = 1,430 * V * 0.0254/18.9

V = 1,040 m/s (This ignores shear thinning.)

Example 1


(Pa·s), (equivalent second-pascalthe

to N·s/m2, or kg/(m·s)).

http://en.wikipedia.org/wiki/Second

http://en.wikipedia.org/wiki/Pascal_(unit)

The desired volume flow rate of the molten metal into a mold is 0.01 m3/min.

The top of the sprue has a diameter of 20 mm and its length is 200 mm.

What diameter should be specified at the bottom of the sprue in order to

prevent aspiration?

What is the resultant velocity and Reynolds number at the bottom of the sprue

if the metal being cast is aluminium and has a viscosity of 0.004 N-s/m2

Solution

Since d1 = 0.02 m

The metal volume flow rate is Q= 0.01 m3/min = 1.667×10-4 m3/s 1Top, 2 bottom

Therefore

Example 5.2 Design and analysis of a sprue for casting

m/s 531.01014.3

10667.14

4

1

1

A

Qv

2422

1 m 1014.302.044

dA


m/s 45.12 v

Assuming no frictional losses, and recognizing that the pressure at the top and

bottom of the sprue is atmospheric

Thus,

fg

v

g

ph

g

v

g

ph

2

2

2

222

2

111

0

81.92

81.92

531.02.0

2

2

2

v

g

p

g

p atmatm

24

2 m 1015.1 A22vAQ 45.1101.667 2

4 A

2

24

dA

24

41015.1 d

mmd 12


745,11

004.0

2700012.045.1Re

vD

In calculating the Reynolds number

3/2700 mkg

As stated above, this magnitude is typical for casting molds, representing

a mixture of laminar and turbulent flow

An Re value of up to 2000 represents laminar flow

An Re Between 2000 and 20,000 it is a mixture of laminar and turbulent

flow and is generally regarded as harmless in gating systems for casting

Re values in excess of 20,000 represent severe turbulence.


D = diameter of the

channel

ρ = density

n = viscosity of the liquid.


Physical Properties of Materials

TABLE 3.3 Physical

Properties of Various

Materials at Room

Temperature.


Casting Alloys


P.P.P File Prepared by the author and publisher and other sources

Shrinkage

Shrinkage in casting causes dimensional changes.

Cracking is a result of:

1. Contraction of the molten metal

2. Contraction of the metal during phase change

3. Contraction of the solidified metal

For L->S, always think of

Solidification Shrinkage!!



Heat transfer

Heat flow depends on casting material and the

mold and process parameters.

Temperature distribution in the mold-liquid

metal interface is shown below.


Solidification time

Solidification time is a function of the volume of

a casting and surface area (Chvorinov’s rule).

Effects of mold geometry and elapsed time on

skin thickness and its shape are show.

n

C

Area Surface

Volumetion timeSolidifica C = constant

n = 2


Temperature vs. Time

Chvorinov’s rule for solidification time for a conducting mold

Chvorinov’s rule for solidification time for an insulating mold

t = cooling time

K = a constant

V = volume

A = area

2

A

VKt


Solidification time (t)

A

VKt

22

,int_

1

4

casting

casting

moldmoldmoldinitilmoldpomelting

CastingCasting

A

V

ckTTt

casting

casting

initilmoldpomelting

CastingCasting

A

V

TTht

,int_

Solidification time (t) for an insulating mold (α mold << α casting; k mold << k

casting)

Solidification time (t) for a conducting mold (Biot # =hl/k < 0.17)

ΔH = latent heat for the process = Hf + ΣCiΔT

Hf = latent heat of solidification (fusion)

V = volume

A = area

h = heat transfer coefficient

C = specific heat

ρ = density Source : Manufacturing Processes for Engineering Materials,5rd Edition., S. Kalpakjian and S. Schmid, 2008 , Additional references in the last slide

=Thermal Diffusivity

K=Thermal Conductivity

T pf C

Thermal Diffusivity

Conductivity K

Thermal Diffusivity ( )

Cooling time (t) for a solid object for a small Biot number (Biot # =hl/k < 0.17)

finalcastingpomelting

initilcastingmoldcastingcasting

casting

casting

TT

TT

h

C

A

Vt

,int_

,ln


Solidification time – Ex. 1

• You are sand casting a magnesium part with

dimensions of 10 cm by 10 cm by 2.5 cm.

The environment temperature is 25o

C.

• Determine the time for the part to solidify if

the metal is poured at its melting point.

• Determine the time for the part to solidify if

the metal is poured at 50oC above its melting

point, so as to alleviate the potential problem

of short shots.

Solidification time


C = specific heat

ρ = density

• N.B. solidification is a phase change

that occurs at the melting point

• Insulating mold:

– kmold = 0.6 << kcasting = 156 W/m-K

– mold = 3.4 x 10-7 << casting = 6.6 x 10-5 m2/s

• Solidification time:

22

,int_

1

4

casting

casting


CastingfCasting

A

V

ckTTt

• = 384 kJ/kg

• = 1700 kg/m3

• Tm = 650oC

• To = 25oC

• km = 0.6 x 10-3

kW/m-K

• = 1500 kg/m3

• cm = 1.16 kJ/kg-K

f


ρ = density

• V = 0.1 x 0.1 X 0.025 = 2.5 x 10-4

m3

• A = 2 x (0.1 x 0.1) + 4 X (0.1 x 0.025) =

A = 0.03 m2

• (V/A) = 8.33 x 10-3

m

• (V/A)2 = 6.94 x 10

-5 m

2

kJ/kg843x038.1384

T

pf C

ΔH = latent heat for the process

st

t

A

V

ckTTt

So

casting

casting


CastingfCasting

57

10×94.61.16×1500×10×6.0

1

25650

384×1700

4

1

4

5

3

2

22

,int_

• Now, we have to take into account

cooling the liquid from (650 + 50)oC to

650 oC

• So, the latent heat of solidification ( )

will be increased by cpT

22

,int_

1

4

casting

casting


CastingfCasting

A

V

ckTTt

f

453kJ/kg50x 38.1384

T

pf C

• For liquid magnesium

– cp = 1.38 kJ/kg-K

• So

CT 50650700

st

t

A

V

ckTTt

So

casting

casting


CastingfCasting

79

10×94.61.16×1500×10×6.0

1

25650

453×1700

4

1

4

5

3

2

22

,int_

(a bit slower)

• In both cases, we need to be careful

that the part does not freeze before

filling the mold (short shot).

• To be conservative, complete the pour

in 79 – 57 = 22 s

– superheating-allowed time

Conducting mold

• We can perform a similar analysis

when the mold conducts as well as the

metal being cast and the interface

resistance dominates.

• Die casting is an example.

casting

casting

initilmoldpomelting

CastingCasting

A

V

TTht

,int_


ΔH = latent heat for the process = Hf + ΣCiΔT


V = volume

A = area

h = heat transfer coefficient

C = specific heat

ρ = density


=Thermal Diffusivity

K=Thermal Conductivity

T pf C

.h=The overall heat transfer coefficient


casting

casting

initilmoldpomelting

CastingCasting

A

V

TTht

,int_

Material properties:

Data for solid materials at room temperature

Thermal

conductivity

(k) (W/m-oC)

Density (ρ)

(kg/m3)

Specific heat (C)

(kJ/kg-oC)

Material

0.60 1500 1.16 Sand

202 2700 0.90 Aluminum

92 8910 0.44 Nickel

156 1700 1.07 Magnesium

385 8970 0.39 Copper

42.7 7125 0.441 Gray cast iron


Viscosity

() (mPa-s)

Specific heat (C)

(kJ/kg-oC)

Latent heat of

solidification

(fusion)

(Hf) (kJ/kg)

Melting point

(oC) Material

1.3 1.05 396 660 Aluminum

--- 0.73 297 1453 Nickel

1.04 1.38 384 650 Magnesium

2.1 0.52 220 1083 Copper

5.25 0.34 211 1251 Gray cast

iron

Data for liquid materials


moldtotaltotal

gate

moldf hhh

gA

At

2

2

total

bapouring

sprueofbottom

sprueoftop

sprueoftop

spreueofbottom

h

h

v

v

A

A sin,

..

..

..

..

Filling time for a bottom-gated mold

For no aspiration

Mold filling time estimate

gategatevA

volumeMoldt

.




k=202w/m-oc ,.h=5000w/m2-c


Melting Practice and Furnaces

Melting has a direct bearing on the quality of castings.

Fluxes are inorganic compounds that refine the molten

metal by removing dissolved gases and various

impurities.

The metal charge may be composed of commercially

pure primary metals, which can include remelted or

recycled scrap.


Three pieces being cast have the same volume but different shapes. One is

a sphere, one a cube, and the other a cylinder with a height equal to its

diameter. Which piece will solidify the fastest and which one the slowest?

Use n = 2.

Solution

The volume is unity

Respective surface areas are

Respective solidification times t are

Example 5.3

Solidification times for various solid shapes

54.522 :Cylinder

66 : Cube

84.44

34 :Sphere

2

2

3/2

rhrA

aA

A

2area Surface

1tion timeSolidifica

CtCCt cylindersphere 033.0 028.0 043.0 c ubet


Bibliography (References)

. Manufacturing Processes for Engineering Materials,5rd Edition., S. Kalpakjian and S. Schmid, Prentice Hill

2008

Materials and Processes in Manufacturing, 10th Edition, E. Paul DeGarmo, J. T. Black, Ronald A.

Kohser,2007.

Manufacturing Engineering & Technology , Serope Kalpakjian , 6th Edition, Prentice Hall,2009.

TECNOLOGI CO DE MONTERREY Mechanical Manufacturing, Professor Arturo Molina , October 2004.

E. Paul DeGarmo et al, “Materials And Processes in Manufacturing”, Wiley Publishing Company 2003.

John E. Schey, “Introduction To Manufacturing Processes” McGraw-Hill Book Company,1988.

Courtney, T. H., “ Mechanical Behavior of Materials”, N. Y., McGraw-Hill, 1990.

E., George E. and George F., “ The Testing of Engineering Materials”, McGrraw-Hill Book Company.

1982.

“Hardness Tests”, Metals Park, Ohio: ASM International, 1987.

Harmer E., George E. and George F., “ The Testing of Engineering Materials”, McGrraw-Hill Book

Company. 1982.

Halmshaw R. “ Non-Destructive Testing”, Edward Arnold, 1991.

Courtney, T. H., “ Mechanical Behavior of Materials”, N. Y., McGraw-Hill, 1990.

Jonathan S. Colton , Manufacturing Processes and Engineering, Georgia Institute of Technology, 2009.

Pohlandt K., “ Material Testing for Metal forming Industry”, N.Y Springer 1989.

Lawrence E. Doyle, “Manufacturing Process And Materials For Engineers”, Prentice-Hall, Third

Edition.

T.T. EL-Midany & M.A. Mansour , Manufacturing Technology, King Abdulaziz University.

S.F. Kvav et al., Machine Tool Operations, McGraw-Hill Book Company.

Geoffrey Boothroyd, Fundamentals of Metal Machining and Machine Tools, McGraw-Hill Book

Company.

Cold and Hot Forging Fundamentals and Applications, Taylan Altan ,al, ASM,2007.

Fundamentals of Metal Forming ,Robert H. Wagoner,Jean-Loup,Wiley,1997.

Metal Forming ,Willam F. Hosford Robert M. ,second Edition, PTR, 1993.

http://eu.wiley.com/WileyCDA/Section/id-302479.html?query=E.+Paul+DeGarmo

http://eu.wiley.com/WileyCDA/Section/id-302479.html?query=J.+T.+Black

http://eu.wiley.com/WileyCDA/Section/id-302479.html?query=Ronald+A.+Kohser

http://eu.wiley.com/WileyCDA/Section/id-302479.html?query=Ronald+A.+Kohser

Documents

Metal Casting Processesstaff.psu.edu.eg/sites/default/files/habdelhafez/files/metal-casting_processes-2.pdfInvestment Casting Procedure: 1. Wax Injection: Wax replicas (patterns of