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Transcript of Lect2 Casting
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Metal-Casting Processes andEquipment
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Solidification Processes
Starting work material is either a liquid or is in ahighly plastic condition, and a part is createdthrough solidification of the material
• Solidification processes can be classifiedaccording to engineering material processed:
• Metals
• Ceramics, specifically glasses• Polymers and polymer matrix composites(PMCs)
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Casting
Process in which molten metal flows by gravity or otherforce into a mold where it solidifies in the shape ofthe mold cavity
• The term casting also applies to the part made in theprocess
• Steps in casting seem simple:
1. Melt the metal
2. Pour it into a mold
3. Let it freeze
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Capabilities and Advantages ofCasting
• Can create complex part geometries
• Can create both external and internalshapes
• Some casting processes are net shape; others are near net shape
• Can produce very large parts• Some casting methods are suited to mass
production
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Disadvantages of Casting
• Different disadvantages for different castingprocesses:
• Limitations on mechanical properties
• Poor dimensional accuracy and surfacefinish for some processes; e.g., sandcasting
• Safety hazards to workers due to hotmolten metals
• Environmental problems
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Parts Made by Casting
• Big parts: engine blocks and heads forautomotive vehicles, wood burning stoves,machine frames, railway wheels, pipes,
church bells, big statues, and pumphousings
• Small parts: dental crowns, jewelry, small
statues, and frying pans• All varieties of metals can be cast, ferrous
and nonferrous
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Typical Cast Parts
(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) ThePolaroid 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.
(a)
(b)
(c)
(d)
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
The Mold in Casting
• Contains cavity whose geometry determinespart shape
•Actual size and shape of cavity must beslightly oversized to allow for shrinkage ofmetal during solidification and cooling
• Molds are made of a variety of materials,including sand, plaster, ceramic, andmetal
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Temperature & Density for Castings
Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
FIGURE 5.1 (a) Temperature as a function of time for the solidification of pure metals. Note thatfreezing takes place at a constant temperature. (b) Density as a function of time.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Two-Phased Alloys
FIGURE 5.2 (a) Schematic illustration of grains, grain boundaries, and particles dispersed throughout the structure of atwo-phase system, such as lead-copper alloy. The grains represent lead in solid solution of copper, and the particles arelead as a second phase. (b) Schematic illustration of a two-phase system, consisting of two sets of grains: dark andlight. Dark and light grains have their own compositions and properties.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Phase Diagram for Nickel-Copper
FIGURE 5.3 Phase diagram for nickel-copper alloy system obtained by a low rate of solidification. Note that pure nickeland pure copper each have one freezing or melting temperature. The top circle on the right depicts the nucleation ofcrystals; the second circle shows the formation of dendrites; and the bottom circle shows the solidified alloy with grainboundaries.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Irn-Iron Carbide Phase Diagram
FIGURE 5.4 (a) The iron-iron carbide phase diagram. (b) Detailed view of the microstructures above and below theeutectoid temperature of 727°C (1341°F). Because of the importance of steel as an engineering material, this diagramis one of the most important phase diagrams.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Texture in Castings
FIGURE 5.5 Schematic illustration of three cast structures of metals solidified in a square mold: (a) puremetals, with preferred texture at the cool mold wall. Note in the middle of the figure that only favorableoriented grains grow away from the mold surface; (b) solid-solution alloys; and (c) structure obtained byheterogeneous nucleation of grains.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Alloy Solidification & Temperature
FIGURE 5.6 Schematic illustration of alloy solidification and temperature distribution in the solidifying metal.Note the formation of dendrites in the semi-solid (mushy) zone.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Solidification Patterns for Gray CastIron
FIGURE 5.7 Schematic illustration of three basic types of cast structures: (a) columnar dendritic; (b)equiaxed dendritic; and (c) equiaxed nondendritic. Source: After D. Apelian.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Cast Structures
FIGURE 5.9 Schematic illustration of cast structures in (a) planefront, single phase, and (b) plane front, two phase. Source: After D.Apelian.
FIGURE 5.8 Schematic illustration of threebasic types of cast structures: (a) columnardendritic; (b) equiaxed dendritic; and (c)equiaxed nondendritic. Source: After D.Apelian.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Mold Features
FIGURE 5.10 Schematic illustration of a typical sand mold showing various features.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Temperature Distribution
FIGURE 5.11 Temperature distribution at the mold wall and liquid-metal interface during solidification of metals in casting
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Skin on Casting
FIGURE 5.12 Solidified skin on a steel casting; theremaining molten metal is poured out at the times indicatedin the figure. Hollow ornamental and decorative objects aremade by a process called slush casting, which is based onthis principle. Source: After H.F. Taylor, J. Wulff, and M.C.
Flemings.
Chvorinov’s Rule:
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Shrinkage
TABLE 5.1 Volumetric solidification contraction orexpansion for various cast metals.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Cast MaterialProperties
FIGURE 5.13 Mechanical properties for
various groups of cast alloys. Compare withvarious tables of properties in Chapter 3.Source: Courtesy of Steel Founders' Societyof America.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
General Characteristics of Casting
TABLE 5.2 General characteristics of casting processes.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Properties & Applications of Cast Iron
TABLE 5.4 Properties and typical applications of castirons.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Nonferrous Alloys
TABLE 5.5 Typical properties of nonferrous casting alloys.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Microstructure for Cast Irons
FIGURE 5.14 Microstructure for cast irons. (a) ferritic gray iron with graphite flakes; (b) ferritic nodular iron, (ductile
iron) with graphite in nodular form; and (c) ferritic malleable iron. This cast iron solidified as white cast iron, with thecarbon present as cementite (Fe 3C), and was heat treated to graphitize the carbon.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Continuous-Casting
FIGURE 5.15 (a) The continuous-casting process for steel. Note that theplatform is about 20 m (65 ft) aboveground level. Source: AmericanFoundrymen's Society. (b) Continuousstrip casting of nonferrous metal strip.Source: Courtesy of Hazelett Strip-Casting Corp.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Production Steps in Sand-Casting
Outline of production steps in a typical sand-casting operation.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Sand Mold
Schematic illustration of a sand mold, showing various features.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Pattern Plate
A typical metal match-plate pattern used in sand casting.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Design for Ease of Removal fromMold
Taper on patterns for ease of removal from the sand mold
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Sand Cores
Examples of sand cores showing core prints and chaplets to support cores.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Vertical Flaskless Molding
Vertical flaskless molding. (a) Sand is squeezed between two halves ofthe 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.
(c)
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
SandCasting
FIGURE 5.16 Schematic illustration of the sequence of operations in sand casting. (a) A mechanical drawing of thepart, used to create patterns. (b-c) Patterns mounted on plates equipped with pins for alignment. Note the presence ofcore prints designed to hold the core in place. (d-e) Core boxes produce core halves, which are pasted together. Thecores will be used to produce the hollow area of the part shown in (a). (f) The cope half of the mold is assembled bysecuring the cope pattern plate to the flask with aligning pins, and attaching inserts to form the sprue and risers. (g) Theflask is rammed with sand and the plate and inserts are removed. (h) The drag half is produced in a similar manner. (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 andsecuring the assembly with pins. (l) After the metal solidifies, the casting is removed from the mold. (m) The sprue andrisers 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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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Shell-Molding Process
FIGURE 5.17 Schematic illustration of the shell-molding process, also called the dump-box technique.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Caramic Mold Manufacture
FIGURE 5.18 Sequence of operations in making a ceramic mold.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Evaporative Pattern Casting
FIGURE 5.20 Schematic illustration of the expendable-pattern casting process, also known aslost-foam or evaporative-pattern casting.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Investment Casting
FIGURE 5.21 Schematic illustration of investment casting (lost wax process). Castings by thismethod can be made with very fine detail and from a variety of metals. Source: Steel Founders'Society of America.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Automated ShellProduction
A robot generates a ceramic shellon wax patterns (trees) for
investment casting. The robot isprogrammed to dip the trees andthen place them in an automateddrying system. With many layers,a thick ceramic shell suitable for
investment casting is formed.
Source : Courtesy of WisconsinPrecision Casting Corporation
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Integrally Cast Rotor for a GasTurbine
Investment casting of an integrally cast rotor for a gas turbine. (a) Waxpattern assembly. (b) Ceramic shell around wax pattern. (c) Wax is meltedout and the mold is filled, under a vacuum, with molten superalloy. (d) Thecast rotor, produced to net or near-net shape. Source : Courtesy of Howmet
Corporation.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Rotor Microstructure
FIGURE 5.22 Microstructure of a rotor that has been investment cast (top) andconventionally cast (bottom). Source: Advanced Materials and Processes , October1990, p. 25. ASM International.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Pressure & Hot-Chamber Die Casting
FIGURE 5.23 The pressure casting
process, utilizing graphite molds for theproduction of steel railroad wheels.Source: Griffin Wheel Division of AmstedIndustries Incorporated.
FIGURE 5.24 Schematic illustration of the hot-
chamber die-casting process.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Cold-Chamber Die Casting
FIGURE 5.25 Schematic illustration of the cold-chamber die-casting process. These machines arelarge compared to the size of the casting, becausehigh forces are required to keep the two halves ofthe die closed under pressure.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Properties of Die-Casting Alloys
TABLE 5.6 Properties and typical applications of common die-castingalloys.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Types of Cavities in Die-Casting Die
Various types of cavities in a die-casting die. Source: Courtesy of American Die Casting Institute.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Centrifugal Casting
FIGURE 5.26 Schematic illustration of the centrifugal casting process. Pipes, cylinder liners,
and similarly shaped hollow parts can be cast by this process.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Semicentrifugal Casting
FIGURE 5.27 (a) Schematic illustration of the semicentrifugal casting process. Wheels with spokes canbe cast by this process. (b) Schematic illustration of casting by centrifuging. The molds are placed at theperiphery of the machine, and the molten metal is forced into the molds by centrifugal forces.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Squeeze-Casting
FIGURE 5.28 Sequence of operations in the squeeze-casting process. This process combinesthe advantages of casting and forging.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Turbine Blade Casting
FIGURE 5.29 Methods of casting turbine blades: (a) directional solidification; (b) method toproduce a single-crystal blade; and (c) a single-crystal blade with the constriction portion stillattached. Source: (a) and (b) After B.H. Kear, (c) Courtesy of ASM International.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Crystal Growing
FIGURE 5.30 Two methods of crystal growing: (a) crystal pulling (Czochralski process) and (b) floating-zone method. Crystal growing is especially important in the semiconductor industry. (c) A single-crystalsilicon ingot produced by the Czochralski process. Source: Courtesy of Intel Corp.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Melt-Spinning Process
FIGURE 5.31 (a) Schematic illustration of the melt-spinning process to produce thin strips of
amorphous metal. (b) Photograph of nickel-alloy production through melt-spinning. Source: Courtesy of Siemens AG.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Types of Melting Furnaces
Two types of melting furnaces used in foundries: (a) crucible,and (b) cupola.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Austenite-Pearlite Transformation
FIGURE 5.32 (a) Austenite to pearlitetransformation of iron-carbon alloys as afunction of time and temperature. (b) Isothermaltransformation diagram obtained from (a) for atransformation temperature of 675°C (1247°F).(c) Microstructures obtained for a eutectoidiron-carbon alloy as a function of cooling rate.Source: Courtest of ASM International.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Phase Diagram for Aluminum-Copper
FIGURE 5.33 (a) Phase diagram for the aluminum-copper alloy system. (b) Variousmicrostructures obtained during the age-hardening process.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Outline of Heat Treating
TABLE 5.7 Outline of heattreatment processes forsurface hardening.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Heat Treatment Temperature Ranges
FIGURE 5.34 Temperature ranges for heat treating plain-carbon steels, as
indicated on the iron-iron carbide phase diagram.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Casting Processes Comparison
TABLE 5.8 Casting Processes, and their Advantages and Limitations.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Chills
FIGURE 5.35 Various types of (a) internal and (b) external chills (dark areas at corners), used incastings to eliminate porosity caused by shrinkage. Chills are placed in regions where there is a largervolume of metal, as shown in (c).
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Hydrogen Solubility in Aluminum
FIGURE 5.36 Solubility of hydrogen in aluminum. Note the sharp decrease in solubility as the molten metal begins to solid
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Elimination of Porosity in Castings
FIGURE 5.37 (a) Suggested design modifications to avoid defects in castings. Note that sharp corners
are avoided to reduce stress concentrations; (b, c, d) examples of designs showing the importance ofmaintaining uniform cross-sections in castings to avoid hot spots and shrinkage cavities.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Design Modifications
FIGURE 5.38 Suggesteddesign modifications to avoiddefects in castings. Source: Courtesy of The NorthAmerican Die CastingAssociation.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
© 2008, Pearson EducationISBN No. 0-13-227271-7
Economics of Casting
FIGURE 5.39 Economic comparison of making a part by two different casting processes. Note that because of the highcost of equipment, die casting is economical mainly for large production runs. Source: The North American Die CastingAssociation.
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Manufacturing Processes for Engineering Materials, 5th ed.Kalpakjian • Schmid
Lost-Foam Casting of Engine Blocks
FIGURE 5.40 (a) An engine block for a 60-hp 3-cylinder marine engine, produced by the lost-foamcasting process; (b) a robot pouring molten aluminum into a flask containing a polystyrene pattern. Inthe pressurized lost-foam process, the flask is then pressurized to 150 psi (1000 kPa). Source: Courtesy of Mercury Marine