Chapter 11
Metal-Casting Processes
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Summary of Casting Processes
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Typical Cast Parts
(c)
(a)
(b)
(d)
Figure 11.1 (a) Typical gray-iron castings used in automobiles, including the transmission
valve body (left) and the hub rotor with disk-brake cylinder (front). Source: Courtesy of
Central Foundry Division of General Motors Corporation. (b) A cast transmission housing.
(c) The Polaroid PDC-2000 digital camera with a AZ191D die-cast high-purity magnesium
case. (d) A two-piece Polaroid camera case made by the hot-chamber die-casting process.
Source: Courtesy of Polaroid Corporation and Chicago White Metal Casting, Inc.
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Characteristics of Casting
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Production Steps in Sand-Casting
Figure 11.2 Outline of production steps in a typical sand-casting operation.
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Sand Mold
Figure 11.3 Schematic illustration of a sand mold, showing various features.
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Pattern Plate
Figure 11.4 A typical metal match-plate pattern used in sand casting.
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Design for Ease of Removal from Mold
Figure 11.5 Taper on patterns for ease of removal from the sand mold
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Sand Cores
Figure 11.6 Examples of sand cores showing core prints and chaplets to support cores.
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Vertical Flaskless Molding
(c)
Figure 11.7 Vertical flaskless molding. (a) Sand is squeezed between two
halves of the pattern. (b) Assembled molds pass along an assembly line
for pouring. (c) A photograph of a vertical flaskless molding line. Source:
Courtesy of American Foundry Society.
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Sequence of
Operations for
Sand-Casting
Figure 11.8 Schematic illustration of the sequence of operations for sand casting. (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 on next slide.
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Sequence of
Operations for
Sand-Casting,
Cont.
(g) The flask is rammed with sand and rthe plate and inserts are removed. (h) 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 securing the assembly with pins.
The flasks the are subjected to pressure to counteract 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). Source: Courtesy of Steel Founders Society of America
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Shell-Molding Process
Figure 11.9 The shell-molding process, also called dump-box technique.
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Sequence of Operations in Making a Ceramic Mold
Figure 11.10 Sequence of operations in making a
ceramic mold. Source: Metals Handbook, Vol. 5, 8th ed.
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Expandable-Pattern Casting Process
Figure 11.11 Schematic illustration of the expandable-pattern casting process, also
known as lost-foam or evaporative casting.
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Evaporative Pattern Casting of an Engine Block
(a)
(b)
Figure 11.12 (a) Metal is poured into mold for lost-foam casting of a 60-hp. 3-cylinder
marine engine; (b) finished engine block. Source: Courtesy of Mercury Marine.
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Investment Casting Process
Figure 11.13 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: Courtesy of Steel Founders Society of America.
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Integrally Cast Rotor for a Gas Turbine
Figure 11.14 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: Courtesy of
Howmet Corporation.
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Comparison of Investment-Cast and
Conventionally Cast Rotors
Figure 11.15 Cross-section and microstructure of two rotors: (top)
investment-cast; (bottom) conventionally cast. Source: Advanced
Materials and Processes, October 1990, P. 25. ASM International.
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Vacuum-Casting
Figure 11.16 Schematic illustration of the vacuum-castin process. Note that
the mold has a bottom gate. (a) Before and (b) after immersion of the mold
into the molten metal. Source: After R. Blackburn.
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Hot-Chamber Die-Casting
Figure 11.17 Schematic illustration of the hot-chamber die-casting process.
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Cold-Chamber Die-Casting
Figure 11.18 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 dies closed under pressure.
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Properties and Applications of Die-Casting Alloys
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Types of Cavities in Die-Casting Die
Figure 11.19 Various types of cavities in a die-casting die.
Source: Courtesy of American Die Casting Institute.
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Centrifugal-Casting Process
Figure 11.20 (a) Schematic illustration of the centrifugal-casting process. Pipes,
cylinder liners, and similarly shaped parts can be cast with this process. (b) Side
view of the machine.
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Semicentrifugal Casting and Casting by Centrifuging
Figure 11.21 (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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Squeeze-Casting
Figure 11.22 Sequence of operations in the squeeze-casting process.
This process combines the advantages of casting and forging.
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Methods of Casting Turbine Blades
(c)
Figure 11.23 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) After B. H. Kear, (c) Courtesy of ASM International.
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Crystal Growing
Figure 11.24 Two methods of crystal growing: (a)
crystal pulling (Czochralski process) and (b) the
floating-zone method. Crystal growing is important
especially in the semiconductor industry. (c) A singlecrystal ingot produced by the Czochralski process.
Source: Courtesy of Intel Corp.
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(c)
Melt-Spinning
(b)
Figure 11.25 (a) Schematic illustration of melt-spinning to produce thin strips of
amorphous metal. (b) Photograph of nickel-alloy production through melt-spinning.
Source: Siemens AG
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Types of Melting Furnaces
Figure 11.26 Two types of melting furnaces used in foundries:
(a) crucible, and (b) cupola.
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