Casting (MIT 2.008x Lecture Slides)

2.008x
Casting
MIT 2.008x
Prof. John Hart

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What is casting?
Why is it a useful and
important manufacturing
process?
How does it compare
and contrast to
processes we have
studied already?

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à Casting is the process
whereby a part is produced by
solidification (of a molten
metal) to take the shape of a
mold.
à Why casting?
§ Versatile to many types of
metals
§ Potential for rapid and cost-
effective production
§ Wide range of length scales
(mm to m!)
§ Complex part geometries
(including internal cavities)
Engine block by 160SX (talk) - 160SX (talk)'s file, CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=7899838
Brass rat by Pigsfly33 at English Wikipedia, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=31980643,

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Casting and history
Bessemer steel converter (enabled reduction of
carbon content in Iron à steel), 1865
http://www.metmuseum.org/art/collection/search/257580
https://www.metmuseum.org/toah/works-of-art/28.77/
https://en.wikipedia.org/wiki/Bessemer_process#/media/File:Bessemer_converter.jpg (Public
domain)
Left: Bronze statue of a man,
Hellenistic period, mid-2nd-
1st
century B.C., H. 73 in (185.4 cm)
Below: Herakles (Son of Zeus)

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The engine from the 1903 Wright Flyer had an aluminum crankcase. The Wrights
contracted a local Dayton foundry, the Buckeye Iron and Brass Works, to cast the
aluminum crankcase. Buckeye acquired their raw aluminum from the nearby Pittsburgh
Reduction Company, renamed Alcoa in 1907, the world’s leading producer of aluminum.
http://airandspace.si.edu/explore-and-learn/multimedia/detail.cfm?id=5817

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Global cast iron and steel production
(millions of tons)
World census of casting production:
http://www.afsinc.org/multimedia/contentMCDP.cfm?ItemNumber=16433

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Agenda:
Casting
§ Classification of casting methods
§ Sand casting
§ Die casting
§ Casting process physics:
§ Fluidity and cooling (with
demonstration)
§ Solidification and microstructure
§ Investment casting
§ Comparison and conclusion

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Casting:
2.Classification of
casting methods

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Classification of casting processes
General sequence (all casting processes):
§ Pattern/mold making
§ Melt preparation
§ Mold filling
§ Cooling and solidification
§ Removal (‘breakout’) of the parts
Kalpakjian and Schmid, Manufacturing Engineering and Technology

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Sand casting
Groover, Fundamentals of Modern Manufacturing

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Important criteria for
casting materials
§ Melting point and latent heat
§ Density versus temperature
§ Solubility with other elements
§ Diffusion rates
§ Reactivity (especially to oxygen)
§ Outgassing (vapor pressure)

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3000° C
0° C
1000° C
2000° C
Tungsten Carbide, WC,
Silicon Carbide, SiC
Molybdenum
Alumina Al2O3
Platinum, Pt
Titanium, Ti
IronFE, Plain Carbon Steels, low alloy, stainless
Nickel, Ni
Nickel Allows
Cubic Zirconia, ZrO2
Silicon, Si
Copper, Cu, Bronze, Brass
Aluminum
Magnesium
Zinc, Zn
PTFE (Teflon)
Tin, Sn
HDPE
Nylon
Acetal
Tungsten Carbide (WC)
Silicon Carbide (SiC)
Molybdenum
Alumina (Al2O3;; 2072 oC)
Platinum, Titanium (1668 oC)
Iron and steels, Nickel, Silicon
Copper, Bronze, Brass
Aluminum (660 oC)
Magnesium
Zinc (420 oC)
Tin

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Casting:
3. Sand casting

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Sand casting
https://www.youtube.com/watch?v=HSOtZj2Y8is

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Sand casting
§ Mold cavity is formed by packing
sand around a pattern.
§ Interior geometry is defined by a
core (disposable).
§ The pattern is removed and the
cavity has the desired shape.
§ Sand for the mold is, for example,
90% sand, 3% water and 7% clay.

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Sand casting: key attributes
§ Low surface detail;; post-machining often required for
high tolerances.
§ It’s the most common casting method (by total weight);;
can make VERY large parts.
§ Because mold filling is gravity-driven (more to come
later), must pay most careful attention to flow and
shrinkage.
§ It’s a (relatively) labor-intensive process with long cycle
time (why?)
§ 3D printing of molds and complex cores (though one-
time use) can achieve previously impossible geometries.

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Voxeljet: 3D printed
sand molds

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Casting:
4. Die casting

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Die casting of aluminum wheel caps
https://www.youtube.com/watch?v=N6ODcxK8_lg

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Die casting: attributes
§ Pressure: ~1-1000 MPa (how
does this compare to IM?)
§ Cycle time: ~10’s of seconds for
average components (tools/toys)
§ Parts have many similarities to
IM, i.e., ejector pin marks,
parting lines, gates/runners.
§ Dies are endangered by heat-
induced cracking and corrosion
(accelerated at high
temperature) à need tool-grade
steel or other special materials.

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Die casting: hot chamber method
: cold chamber method

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Hot Wheels!
Image: http://www.amazon.com/Hot-Wheels-9-Car-Gift-Styles/dp/B006EFMSSM

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Which processes?
20 for $15 (Amazon);; how is that possible?

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DFM: Integral rivets!

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Ferrari F12 Berlinetta
Wheelhouses:
sand casting
Frame components:
High pressure die
casting
Top image: screenshot from http://auto.ferrari.com/en_US/sports-cars-models/car-range/f12-berlinetta/#design-360_exterior-5
Bottom image: http://auto.ferrari.com/en_EN/wp-content/uploads/sites/5/2013/07/architecture11.jpg

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Casting:
5. Fluidity and cooling

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Surface tension and viscosity
Ux(H) = Ux
Ux(y)
Ux(0) = 0
h
Ux
y
U
∂
∂
= µτ
Surface tension, σ Dynamic viscosity, μ
Water (25 C) 0.07 N/m 1×10-3 kg/m-s [Pa-s]
Honey (25 C) ~0.06 ~10
Liquid thermoplastic ~0.03 102-103
Molten aluminum (600 C) 0.90 3×10-3

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Fluid flow
considerations for
good casting
à If gravity-driven, pressure ‘head’
must be sufficient to overcome flow
resistance to fully infiltrate mold
cavity.

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Fluid flow
considerations for
good casting
à Flow must remain laminar to
prevent air entrainment.avoid
abrupt direction change. Trapped
air leads to ‘dross’ (oxide flakes)
à same as
μ (viscosity)

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Testing ‘fluidity’ for casting
Al with increasing
content of
reinforcing
particles (SiC)
Behera et al. “Effect of Reinforcement Particles on the Fluidity and Solidification Behavior of the Stir Cast Aluminum Alloy
Metal Matrix Composites”, American Journal of Materials Science, 2012;; 2(3): 53-61

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Demonstration: Cooling in sand casting vs.
die casting (‘wood’s metal’)

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Solidification time
Time [s]
Temperature[°C] 20
Sand Casting
10
30
40
50
60
70
80
Die Casting
2000 400 600 800 1000 1200

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Chvorinov’s rule
§ V = volume of the
casting
§ A = surface area of the
casting
§ C = mold constant,
depends on mold
material and thermal
properties of casting
metal
tsolidify = C ⋅
V
A
"
#
$
%
&
'
n

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Solidification: sand cast versus die cast
TM!
SAND
SOLID!
LIQUID!
T0!
0
tsolidify = C ⋅
V
A
"
#
$
%
&
'
2
αsand ~0.01 cm2/s
TM!
METAL
SOLID!
LIQUID!
0
T0!
αsteel ~0.1 cm2/s
αaluminum ~0.9 cm2/s
tsolidify = C ⋅
V
A
"
#
$
%
&
'
à Like injection molding, but
mold has low thermal conductivity
à Lower-bound (assumes
constant mold temp)

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Casting:
6. Solidification and
microstructure

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Solidification of pure metals
§ Metal releases latent heat as it freezes;; this accounts for
up to ~50% of the energy transfer.
§ As a result, solid and liquid co-exist in the mold for a
significant time.
1/Temperature

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Formation of cast microstructure
Columnar
Shell zone
(‘Chill’)
grain
y
oy
d
k
+= σσ
Hall-Petch model: smaller grains
give higher strength
σ0 = stress to start dislocation movement
ky = material hardening constant
d = grain size
Grain size is
inversely
proportional to
cooling rate.
Shell has finer
grains à
thinner die
cast parts are
typically
stronger

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Alloys: dendrites and the ‘mushy zone’

2.008xWhat causes the voids?

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Shrinkage!

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Casting: general defects
§ Misrun: solidification before complete filling
§ Cold shut: lack of fusion due to premature freezing
§ Cold shot: metal splatter entrapped in casting
§ Shrinkage cavity: depression in surface caused by
solidification shrinkage (or hot tear = internal void)

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Casting:
8. Investment casting

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Investment (‘lost wax’) casting
Image from http://www.custompartnet.com/wu/investment-casting

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An industrial investment casting process
Screenshot from: https://www.youtube.com/watch?v=cptlGzWYFEk

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Investment casting: key points
§ Use of wax template enables excellent surface finish
with little/no post-processing.
§ Ceramic shell enables casting of high melting point
metals/alloys.
§ Metal typically poured in vacuum oven (reduces
defects).
§ Very labor intensive à robots!
Why investment casting?
§ Jewelry: complex geometries, high tolerances and fine
features.
§ Jet engine parts: smooth surface finish, compatibility
with high temperature alloys.

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Image from ATI Aerospace (http://www.slideshare.net/johnpsilk/ati-jet-engine);; see also
http://www.geaviation.com/commercial/engines/genx/;; https://www.youtube.com/watch?v=S1ahHWXGx5Y

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Investment casting of turbine blades
à Careful control of solidification can give single crystal blades (= very
high strength and fatigue life under cyclic load at high temperature)
Image at right from http://www.chromalloy.com/files/newspressrelease/7ac07680-0adb-460b-8f27-f7d47745a4c4.pdf
Great article: ‘The metal that brought you cheap flights’ http://www.bbc.com/news/magazine-32749262

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Casting:
9. Comparison and
conclusion

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What casting method was used and why?
Die casting: Small parts, precision
features, good surface finish
Sand casting: Larger parts, rough
surface finish
Investment casting: Complex curves, good surface finish (at right)
1 2
3
Aluminum castings from the sand mold (modified): photograph taken by Glenn McKechnie - Own work, CC BY-SA 2.0,
An investment cast turbocharger turbine, Nuclear valve by Mark Bolton - CC BY-SA 3.0, https://en.wikipedia.org/w/index.php?curid=10729027,

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Why would I:
à Choose die casting instead of
injection molding?
Need metal (strength, durability)
instead of plastic
à Choose investment casting
instead of die casting?
Higher melting point material,
complex internal cavities, high
precision
à Choose machining instead of die
casting?
Higher tolerances;; better control of
microstructure/properties (can use
wrought/forged material)

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Reflection: the big four
Sand Investment Die
Rate Medium Low High
Quality Low Medium High
Cost Low Medium High
Flexibility Low-Medium Medium Low

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Top image from:
http://www.alcoa.com/global/en/innovation/alcoa_micromill.asp
Article: Automotive News, September 14, 2015.

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Continuous casting of aluminum sheet
(Alcoa ‘micromill’ process)
https://www.youtube.com/watch?v=AH2QcNGM87w
http://www.alcoa.com/global/en/innovation/alcoa_micromill.asp
Furnace (molten Al)
Continuously
moving sheet

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References
1 Introduction
Photo of Fire Hydrant by User: KeystonePetPlace on Pixabay. This work is in the public domain.
Photo of Die Cast BMW Car by User: RockyHorror on Pixabay. This work is in the public domain.
Photo of Cast Elbow Pipes by User: Dyanap on Pixabay. This work is in the public domain.
Photo of Wheel Rims by User: Pashminu on Pixabay. This work is in the public domain.
Photo of Jet Engine Turbine by User: Michael Schwarenberger on Pixabay. This work is in the
public domain.
Photo of Engine Block by 160SX (160SX (talk)'s file) on Wikimedia. (CC BY-SA) 3.0
Photo of Propeller Blade by User: seehund on Pixabay. This work is in the public domain.
Photo of MIT Class Ring by User: Pigsfly33 on Wikimedia. (CC BY-SA) 3.0
Image of Herakles Statue © 2000–2016 The Metropolitan Museum of Art
Image of Bronze Statue of a Man © 2000–2016 The Metropolitan Museum of Art

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References
Image of Bessemer Converter Diagram from "Discoveries & Inventions of the Nineteenth Century"
by R. Routledge, published 1900. This work is in the public domain.
Image of Wright Brothers Engine from the National Air and Space Museum © The Smithsonian.
Image of Wright Brothers Flyer from the National Air and Space Museum © The Smithsonian.
Image of US and China Casting Production © American Foundry Society
Image of Global Cast Iron and Steel Production © IKB Deutsche Industriebank AG
2 Classification
Casting Process Classification: Figure II.3 from "Manufacturing Engineering & Technology (7th
Edition)" by Kalpakjian, Schmid. © Upper Saddle River;; Pearson Publishing (2014).
Sand Casting Mold Features: Figure 10.2 b) from "Fundamentals of Modern Manufacturing (4th
Edition)" by Groover. © John Wiley & Sons Inc. (2010).

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References
3 Sand Casting
Video of Sand Casting © 2006 - 2016 ChinaSavvy. All Rights Reserved.
Sand Casting Mold Features: Figure 10.2 b) from "Fundamentals of Modern Manufacturing (4th
4 Die Casting
Video of Die Casting © 2016 Die Castings China
Hot Chamber Die Casting: Figure 11.13 1) and 2) from "Fundamentals of Modern Manufacturing
(4th Edition)" by Groover. © John Wiley & Sons Inc. (2010).
Cold Chamber Die Casting: Figure 11.14 1) and 2) from "Fundamentals of Modern Manufacturing
(4th Edition)" by Groover. © John Wiley & Sons Inc. (2010).
Image of Ferrari F12 Berlinetta by Ferrari S.p.A. Copyright 2016. All Rights Reserved.
Image of Ferrari Aluminum Chassis by Ferrari S.p.A. Copyright 2016. All Rights Reserved.

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References
5 Fluidity / Cooling
Gated Casting with Risers: Figure 10.8 from "Manufacturing Engineering & Technology (7th
Spiral Test Casting: Figure 10.9 from "Manufacturing Engineering & Technology (7th Edition)" by
Kalpakjian, Schmid. © Upper Saddle River;; Pearson Publishing (2014).
Image of Changing Fluidity Index © 2012 Scientific & Academic Publishing
Temperature Distribution at Mold Wall: Figure 10.10 from "Manufacturing Engineering &
Technology (7th Edition)" by Kalpakjian, Schmid. © Upper Saddle River;; Pearson Publishing
(2014).
6 Solidification
Temperature Evolution over Time: Figure 10.1 a) from "Manufacturing Engineering & Technology
(7th Edition)" by Kalpakjian, Schmid. © Upper Saddle River;; Pearson Publishing (2014).
Change in Specific Density: Figure 10.1 b) from "Manufacturing Engineering & Technology (7th

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References
Casting Cross-Section: Figure 10.2 b) from "Manufacturing Engineering & Technology (7th
Phase Diagram: Figure 10.4 from "Manufacturing Engineering & Technology (7th Edition)" by
Kalpakjian, Schmid. © Upper Saddle River;; Pearson Publishing (2014).
7 Defects
Shrinkage and Cavity Formation: Figure 10.8 2) and 3) from "Fundamentals of Modern
Manufacturing (4th Edition)" by Groover. © John Wiley & Sons Inc. (2010).
Shrinkage Allowances: Table 12.1 from "Manufacturing Engineering & Technology (7th Edition)"
by Kalpakjian, Schmid. © Upper Saddle River;; Pearson Publishing (2014).
Common Casting Defects: Figure 11.22 a) - d) from "Fundamentals of Modern Manufacturing (4th

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References
8 Investment Casting
Image of Investment Casting Process © 2009 CustomPartNet
Video of Investment Casting Process ©2011 Wisconsin Precision Casting Corporation
Image of Jet Engine Materials © 2016 ATI. All Rights Reserved.
Single Crystal Turbine Blade: Figure 11.25 b) and c) from "Manufacturing Engineering &
Technology (7th Edition)" by Kalpakjian, Schmid. © Upper Saddle River;; Pearson Publishing
(2014).
Image of Wax Patterns for Turbine Blades © SouthComm Publishing Company 2015.
9 Conclusion
Photo of Threaded Faucet Connection by User: byrev on Pixabay. This work is in the public
domain.
Photo of Bearing by User: petitgiovanni on Pixabay. This work is in the public domain.

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References
Photo of Toy Truck by User: da_hammer on Pixabay. This work is in the public domain.
Photo of Sand Cast Parts by User: Graibeard on Wikimedia. (CC BY-SA) 2.0
Photo of Investment Cast Turbocharger Turbine Blades by MarkBolton at English Wikipedia. (CC
BY-SA) 3.0
Photo of Valve for Nuclear Power Station by MarkBolton at English Wikipedia. (CC BY-SA) 3.0
Compatison of Casting Methods: Table 11.2 from "Manufacturing Engineering & Technology (7th
Image of Micromill © 2016 Alcoa Inc.
Article on F150 Production © Crain Communications, Inc.
Image of Ford F150 Chassis © 2014 Sustainable Enterprises Media, Inc.
Image of Ford F150 © 2016 Ford Motor Company
Image of Micromill Plant © 2016 Alcoa Inc.
Video of Micromilling © 2016 Alcoa Inc.

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