CHAPTER 11
Metal-Casting Processes
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Typical gray-iron 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.
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A cast transmission housing
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Chapter 11
Expendable mold
mold
1 個 workpiece
…
mold
Permanent mold
n 個 workpiece
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Steps in Sand Casting
Figure 11.2 Outline of production steps in a typical sand-casting operation.
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Sand Mold Features
Figure 11.3 Schematic illustration of a sand mold, showing various features.
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Sequence of Operations for Sand Casting
Figure 11.11 (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.
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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 (i) The pattern, flask, and bottom board are inverted, and the pattern is withdrawn, leaving the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).
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Sand
green molding sand 生砂 (砂、黏土、水)
Pattern
1 pattern→n mold ( pattern使用鋁或木材等較易加工的材質)
Taper 錐度 (利於拔模，通常是1°~3 °)
Core print 砂心座
Core print
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Patterns for Sand Casting
Figure 11.4 A typical metal match-plate pattern used in sand casting.
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Figure 11.5 Taper on patterns for ease of removal from the sand mold.
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Examples of
Sand Cores
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Examples of Sand Cores and Chaplets
Figure 11.6 Examples of sand cores showing core prints and chaplets to support cores.
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Lost Foam / Evaporative casting
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Evaporative Pattern Casting of 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 脫蠟鑄造
Pattern (wax)
Mold (ceramics)
Metal casting
優點：
• 可做複雜造型 (∵wax易加工修整，可拼裝複雜造型)
• 表面光滑 (∵ slurry磨粒細)
缺點：
• 無法做大型鑄件
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Investment Casting
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 Founder’s
Society of America.
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Die casting 壓鑄
…
die
n 個 casting
die casting 的材質通常是Al或Cu，熔點比steel 低，故使
用steel die。當casting 材質是steel，就必須使用熔點更高
的模具材料。
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Die-Casting Examples
(a)
(b)
Figure 11.1 (c) The Polaroid PDC-2000 digital camera with a AZ91D die-cast, high purity
magnesium case. (d) 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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-- Good Surface Finish
-- Fine-Grain Structure
-- Volume Production
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Hot-Chamber Die-Casting
Figure 11.17 Schematic illustration of the hot-chamber die-casting process.
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Hot-Chamber Die-Casting Machine
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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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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Cold-Chamber Die-Casting Machine
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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Hot- and Cold-Chamber Die-Casting
-- Metals of low-melting point
(Zn, Sn, Pb)
-- 103 / hr
-- P = 15MPa
-- Metals of high-melting point (Al, Cu, Mg)
-- To avoid contamination at high temperature
-- P = 20-150MPa  fine details (<0.5mm
thin wall)
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Die-Casting Die Cavities
Figure 11.19 Various types of cavities in a die-casting die.
Source: Courtesy of American Die Casting Institute.
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Figure 11.18
Die：Workpiece =1000：1
25~3000 ton 鎖模力
Estimate of Clamping force (鎖模力)
die casting pressure  50M Pa  50N/mm 2
a die cavity of cross section  10 mm
4
2
 Clamping force  50  10 4 N  55 ton
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Advantage of die casting
Fine detail (thin wall<0.5 mm, compared to > 3mm in
sand casting)
Fine surface finish
Fine-grain structure (fast cooling → grain size small)
Highly automated process
Disadvantage of die casting
High equipment cost
(machine：106~107 NTD；die：104~105 NTD)
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TABLE 11.1
Process
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.
Investment
Intricate shapes; excellent
surface finish and accuracy;
almost any metal cast.
Part size limited; expensive
patterns, molds, and labor.
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.
Summary of Casting Processes
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General Characteristics of Casting Processes
TABLE 11.2
Typical
Process
Sand
Shell
Expendable
mold
pattern
Weig ht (kg)
materials
cast
Minimum
Maximum
All
All
0.01
0.01
No limit
100+
Typical
surface
finish
(mm, Ra)
5-25
1-3
Section thic kness (mm)
Shape
Dimensional
Porosity* complexity* accuracy* Minimum
3-5
4-5
1-2
2-3
All
0.01
100+
5-20
3-5
1-2
Nonferrous
Plaster
(Al, Mg, Zn,
mold
Cu)
0.01
50+
1-2
4-5
1-2
All
(High melting
Investment
pt.)
0.001
100+
0.3-2
5
1
Permanent
mold
All
0.1
300
2-6
2-3
2-3
Nonferrous
(Al, Mg, Zn,
Die
Cu)
<0.01
50
1-2
1-3
3-4
Centrifugal
All
0.01
5000+
2-10
1-2
3-4
*Relative rating: 1 best, 5 worst.
Note : These ratings are only general; significant variations can occur, depending on the methods used.
Maximum
3
2
3
2
No limit
--
3
2
--C7
2
1
--
1
1
75
1
2
50
1
3
0.5
2
12
100
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Surface Roughness for
Various Metalworking Processes
Surface roughness in casting and other metalworking processes. See also related chapters for
comparison with other manufacturing processes.
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Crystal Growing
(c)
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 single-crystal ingot produced by the Czochralski process. Source: Courtesy of Intel Corp.
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Ch 11
精讀：11.1~11.2.1, 11.3.2, 11.4.5
略讀：11.3.1, 11.5: Single-crystal Growing
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