Transcript Summary of Casting Processes, Their Advantages and Limitations

CHAPTER 11
Metal-Casting Processes
Kalpakjian • Schmid
Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-1
TABLE 11.1
Process
Summary of
Casting
Processes
Advantages
Limitations
Sand
Almost any metal cast; no limit
to size, shape or weight; low
tooling cost.
Some finishing required;
somewhat coarse finish; wide
tolerances.
Shell mold
Good dimensional accuracy and
surface finish; high production
rate.
Part size limited; expensive
patterns and equipment
required.
Expendable pattern
Most metals cast with no limit
to size; complex shapes
Patterns have low strength and
can be costly for low quantities
Plaster mold
Intricate shapes; good
dimensional accu- racy and
finish; low porosity.
Limited to nonferrous metals;
limited size and volume of
production; mold making time
relatively long.
Ceramic mold
Intricate shapes; close
tolerance parts; good surface
finish.
Limited size.
Investment
Intricate shapes; excellent
surface finish and accuracy;
almost any metal cast.
Part size limited; expensive
patterns, molds, and labor.
Permanent mold
Good surface finish and
dimensional accuracy; low
porosity; high production rate.
High mold cost; limited shape
and intricacy; not suitable for
high-melting-point metals.
Die
Excellent dimensional accuracy
and surface finish; high
production rate.
Die cost is high; part size
limited; usually limited to
nonferrous metals; long lead
time.
Centrifugal
Large cylindrical parts with
good quality; high production
rate.
Equipment is expensive; part
shape limited.
Kalpakjian • Schmid
Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-2
Die-Casting Examples
(a)
(b)
Figure 11.1 (a) The Polaroid PDC-2000 digital camera with a AZ91D die-cast, high purity
magnesium case. (b) Two-piece Polaroid camera case made by the hot-chamber die casting
process. Source: Courtesy of Polaroid Corporation and Chicago White Metal Casting, Inc.
Kalpakjian • Schmid
Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-3
General Characteristics of Casting Processes
TABLE 11.2
Process
Sand
Shell
Expendable
mold
pattern
Typical
materials
cast
Minimum
Maximum
All
All
0.05
0.05
No limit
100+
5-25
1-3
4
4
1-2
2-3
0.05
No limit
5-20
4
0.05
50+
1-2
0.005
100+
0.5
<0.05
--
All
Nonferrous
Plaster
(Al, Mg, Zn,
mold
Cu)
All
(High melting
Investment
pt.)
Permanent
mold
All
Nonferrous
(Al, Mg, Zn,
Die
Cu)
Centrifugal
All
Weig ht (kg)
Typical
surface
finish
(mm, Ra)
Section thic kness (mm)
Shape
Dimensional
Porosity* complexity* accuracy*
Minimum
Maximum
3
2
3
2
No limit
--
1
2
2
No limit
3
1-2
2
1
--
1-3
3
1
1
1
75
300
2-3
2-3
3-4
1
2
50
50
5000+
1-2
2-10
1-2
1-2
3-4
3-4
1
3
0.5
2
12
100
*Relative rating: 1 best, 5 worst.
Note : These ratings are only general; significant variations can occur, depending on the methods used.
Kalpakjian • Schmid
Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-4
Casting Examples
Figure 11.2 Typical grayiron castings used in
automobiles, including
transmission valve body
(left) and hub rotor with
disk-brake cylinder (front).
Source: Courtesy of Central
Foundry Division of General
Motors Corporation.
Figure 11.3 A cast
transmission housing.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-5
Sand Mold Features
Figure 11.4 Schematic illustration of a sand mold, showing various features.
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Manufacturing Engineering and Technology
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Steps in Sand Casting
Figure 11.5 Outline of production steps in a typical sand-casting operation.
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Manufacturing Engineering and Technology
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Pattern Material Characteristics
TABLE 11.3
a
Characteristic
Wood
Aluminum
Rating
Steel
Plastic
Cast iron
Machinability
E
G
F
G
G
Wear resistance
P
G
E
F
E
Strength
F
G
E
G
G
Weightb
E
G
P
G
P
Repairability
E
P
G
F
G
Resistance to:
Corrosionc
E
E
P
E
P
Swellingc
P
E
E
E
E
aE, Excellent; G, good; F, fair; P, poor.
bAs a factor in operator fatigue.
cBy water.
Source : D.C. Ekey and W.R. Winter, Introduction to Foundry Technology. New York.
McGraw-Hill, 1958.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-8
Patterns for Sand Casting
Figure 11.6 A typical metal
match-plate pattern used in
sand casting.
Figure 11.7 Taper on patterns for
ease of removal from the sand mold.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-9
Examples of Sand Cores and Chaplets
Figure 11.8 Examples of sand cores showing core prints and chaplets to support cores.
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Manufacturing Engineering and Technology
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Page 11-10
Squeeze Heads
Figure 11.9 Various designs
of squeeze heads for mold
making: (a) conventional
flat head; (b) profile head;
(c) equalizing squeeze
pistons; and (d) flexible
diaphragm. Source: ©
Institute of British
Foundrymen. Used with
permission.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-11
Vertical Flaskless Molding
Figure 11.10 Vertical flaskless molding. (a) Sand is squeezed between two halves of the pattern. (b)
Assembled molds pass along an assembly line for pouring.
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© 2001 Prentice-Hall
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Sequence of Operations for Sand Casting
Figure 11.11 Schematic illustration of the sequence of operations for sand casting. Source: Steel
Founders' Society of America. (a) A mechanical drawing of the part is used to generate a design for the
pattern. Considerations such as part shrinkage and draft must be built into the drawing. (b-c) Patterns
have been mounted on plates equipped with pins for alignment. Note the presence of core prints designed
to hold the core in place. (d-e) Core boxes produce core halves, which are pasted together. The cores will
be used to produce the hollow area of the part shown in (a). (f) The cope half of the mold is assembled by
securing the cope pattern plate to the flask with aligning pins, and attaching inserts to form the sprue and
risers. (continued)
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Sequence of Operations for Sand Casting (cont.)
Figure 11.11 (g) The flask is rammed with sand and the plate and inserts are removed. (g) The drag half is
produced in a similar manner, with the pattern inserted. A bottom board is placed below the drag and aligned
with pins. (i) The pattern, flask, and bottom board are inverted, and the pattern is withdrawn, leaving the
appropriate imprint. (j) The core is set in place within the drag cavity. (k) The mold is closed by placing the
cope on top of the drag and buoyant forces in the liquid, which might lift the cope. (l) After the metal solidifies,
the casting is removed from the mold. (m) The sprue and risers are cut off and recycled and the casting is
cleaned, inspected, and heat treated (when necessary).
Kalpakjian • Schmid
Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-14
Surface Roughness for Various Metalworking Processes
Figure 11.12 Surface roughness in casting and other metalworking processes. See also Figs. 22.14 and
26.4 for comparison with other manufacturing processes.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-15
Dump-Box Technique
Figure 11.13 A common
method of making shell
molds. Called dump-box
technique, the limitations are
the formation of voids in the
shell and peelback (when
sections of the shell fall off
as the pattern is raised).
Source: ASM International.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-16
Composite Molds
Figure 11.14 (a) Schematic illustration of a semipermanent composite mold. Source: Steel
Castings Handbook, 5th ed. Steel Founders' Society of America, 1980. (b) A composite
mold used in casting an aluminum-alloy torque converter. This part was previously cast in
an all-plaster mold. Source: Metals Handbook, vol. 5, 8th ed.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-17
Expendable Pattern Casting
Figure 11.15
Schematic
illustration of the
expendable
pattern casting
process, also
known as lost
foam or
evaporative
casting.
Kalpakjian • Schmid
Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-18
Ceramic Molds
Figure 11.16 Sequence of operations in
making a ceramic mold. Source: Metals
Handbook, vol. 5, 8th ed.
Figure 11.17 A typical ceramic
mold (Shaw process) for casting
steel dies used in hot forging.
Source: Metals Handbook, vol.
5, 8th ed.
Kalpakjian • Schmid
Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-19
Figure 11.18
Schematic
illustration of
investment
casting, (lostwax process).
Castings by this
method can be
made with very
fine detail and
from a variety of
metals. Source:
Steel Founders'
Society of
America.
Investment
Casting
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Manufacturing Engineering and Technology
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Page 11-20
Investment Casting of a Rotor
Figure 11.19 Investment casting of an integrally cast rotor for a gas turbine. (a) Wax pattern assembly.
(b) Ceramic shell around wax pattern. (c) Wax is melted out and the mold is filled, under a vacuum,
with molten superalloy. (d) The cast rotor, produced to net or near-net shape. Source: Howmet
Corporation.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-21
Investment and Conventionally Cast Rotors
Figure 11.20 Crosssection and
microstructure of two
rotors: (top)
investment-cast;
(bottom) conventionally
cast. Source: Advanced
Materials and
Processes, October
1990, p. 25 ASM
International
Kalpakjian • Schmid
Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-22
Vacuum-Casting Process
Figure 11.21 Schematic illustration of the vacuum-casting process. Note that the mold has a
bottom gate. (a) Before and (b) after immersion of the mold into the molten metal. Source:
From R. Blackburn, "Vacuum Casting Goes Commercial," Advanced Materials and Processes,
February 1990, p. 18. ASM International.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
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Pressure Casting
Figure 11.22 (a) The bottom-pressure casting process utilizes graphite molds for the production of steel
railroad wheels. Source: The Griffin Wheel Division of Amsted Industries Incorporated. (b) Gravitypouring method of casting a railroad wheel. Note that the pouring basin also serves as a riser. Railroad
wheels can also be manufactured by forging.
Kalpakjian • Schmid
Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-24
Hot- and Cold-Chamber Die-Casting
(a)
(b)
Figure 11.23 (a) Schematic illustration of the hot-chamber die-casting process. (b) Schematic
illustration of the cold-chamber die-casting process. Source: Courtesy of Foundry Management and
Technology.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-25
Cold-Chamber Die-Casting Machine
(a)
Figure 11.24 (a) Schematic illustration of a cold-chamber die-casting machine.
These machines are large compared to the size of the casting because large forces are
required to keep the two halves of the dies closed.
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Manufacturing Engineering and Technology
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Hot-Chamber Die-Casting Machine
(b)
Figure 11.24 (b) 800-ton hot-chamber die-casting machine, DAM 8005 (made
in Germany in 1998). This is the largest hot-chamber machine in the world
and costs about $1.25 million.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
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Die-Casting Die Cavities
Figure 11.25 Various types of cavities in a die-casting die. Source: Courtesy of
American Die Casting Institute.
Figure 11.26 Examples of
cast-in- place inserts in die
casting. (a) Knurled
bushings. (b) Grooved
threaded rod.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
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Properties and Typical Applications of
Common Die-Casting Alloys
TABLE 11.4
Ultimate
tensile
strength
(MPa)
Yield
strength
(MPa)
Elongation
in 50 mm
(%)
320
160
2.5
300
150
2.5
Brass 858 (60 Cu)
380
200
15
Magnesium AZ91 B (9 Al-0.7 Zn)
230
160
3
Zinc No. 3 (4 Al)
280
--
10
320
--
7
Alloy
Aluminum 380 (3.5 Cu-8.5 Si)
13 (12 Si)
5 (4 Al-1 Cu)
Applications
Appliances, automotive components,
electrical motor frames and housings
Complex shapes with thin walls, parts
requiring strength at elevated
temperatures
Plumbing fiztures, lock hardware,
bushings, ornamental castings
Power tools, automotive parts, sporting
goods
Automotive parts, office equipment,
household utensils, building hardware,
toys
Appliances, automotive parts, building
hardware, business equipment
Source : Data from American Die Casting Institute
Kalpakjian • Schmid
Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-29
Centrifugal Casting Process
Figure 11.27 Schematic
illustration of the centrifugal
casting process. Pipes,
cylinder liners, and similarly
shaped parts can be cast with
this process.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
Page 11-30
Semicentrifugal Casting
Figure 11.28 (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 force.
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Manufacturing Engineering and Technology
© 2001 Prentice-Hall
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Squeeze-Casting
Figure 11.29 Sequence of operations in the squeeze-casting process. This process combines the
advantages of casting and forging.
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Single Crystal Casting of Turbine Blades
Figure 11.30 Methods of casting turbine blades: (a) directional solidification; (b) method to produce
a single-crystal blade; and (c) a single-crystal blade with the constriction portion still attached.
Source: (a) and (b) B. H. Kear, Scientific American, October 1986; (c) Advanced Materials and
Processes, October 1990, p. 29, ASM International.
(c)
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Single Crystal Casting
Figure 11.31 Two methods of
crystal growing: (a) crystal
pulling (Czochralski process)
and (b) the floating-zone
method. Crystal growing is
especially important in the
semiconductor industry.
Source: L. H. Van Vlack,
Materials for Engineering.
Addison-Wesley Publishing
Co., Inc., 1982.
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Melt Spinning
Figure 11.32 Schematic
illustration of melt-spinning to
produce thin strips of
amorphous metal.
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Types of Melting Furnaces
Figure 11.33 Two types of melting furnaces used in foundries: (a) crucible, and (b) cupola.
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