Mô tả:
ADVANCED MANUFACTURING
ENGINEERING
4: Casting Processes and Equipment
December 2016
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Introduction
• Casting is a manufacturing process where a solid is
melted, heated to proper temperature (sometimes treated
to modify its chemical composition), and is then poured
into a cavity or mould, which contains it in the proper
shape during solidification.
• In a single step, simple or complex shapes can be made
from any metal that can be melted.
• Cast parts range in size from a few of mm and grams
(such as the individual teeth on a zipper), to over 10
metres and many tonnes (such as the huge propellers).
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Introduction
• Casting has marked advantages in the production of
complex shapes, parts having hollow sections or internal
cavities, parts that contain irregular curved surfaces
(except those made from thin sheet metal), very large
parts and parts made from metals that are difficult to
machine.
• Due to these obvious advantages, casting is one of the
most important of the manufacturing processes.
• http://youtu.be/7BI4v0Gqc7k 40 secs
• http://youtu.be/M95bhPrDwA0 7 mins
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Parts Made by Casting
• •Big parts: engine blocks and heads for automotive
vehicles, wood burning stoves, machine frames, railway
wheels, pipes, church bells, big statues, and pump
housings
• •Small parts: dental crowns, jewellery, small statues, and
frying pans
• •All varieties of metals can be cast, ferrous and
nonferrous
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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). (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.
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Casting products
Mymachining.com
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Casting
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Casting
• Process in which molten metal flows by gravity or other force
into a mould where it solidifies in the shape of the mould cavity
• The term casting also applies to the part made in the process
• Steps in casting seem simple:
• 1. Melt the metal
• 2. Pour it into a mould
• 3. Let it freeze
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Temperature & Density for Castings
• Temperature as a function of time for the solidification of
pure metals. Note that freezing takes place at a constant
temperature. (b) Density as a function of time.
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Capabilities and Advantages of Casting
• Can create complex part geometries
• Can create both external and internal shapes
• 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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Disadvantages of Casting
• Limitations on mechanical properties
• Poor dimensional accuracy and surface finish for some
processes; e.g., sand casting
• Safety hazards to workers due to hot molten metals
• Environmental problems
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Casting technology
• Today, it is nearly impossible to design anything that
cannot be cast by one or more of the available casting
processes.
• However, as in all manufacturing techniques, the best
results and economy are achieved if the designer
understands the various options and tailors the design to
use the most appropriate process in the most efficient
manner.
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Casting technology
• The various processes differ primarily in the mould
material (whether sand, metal, or other material) and the
pouring method (gravity, vacuum, low pressure, or high
pressure).
• All of the processes share the requirement that the
materials solidify in a manner that would maximise the
properties, while simultaneously preventing potential
defects, such as:
• shrinkage voids,
• gas porosity, and
• trapped inclusions.
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Classification of casting processes
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Classification of Casting Processes
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Casting processes
• Green Sand Moulding
• Dry Sand moulding
• Precision casting methods
• Chemically Bonded Sand Moulding Processes
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The Mould in Casting
• Contains cavity whose geometry determines part shape
• Actual size and shape of cavity must be slightly oversized
to allow for shrinkage of metal during solidification and
cooling
• Moulds are made of a variety of materials, including sand,
plaster, ceramic, and metal.
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Temperature distribution
• Temperature distribution at the mould wall and liquid-
metal interface during solidification of metals in casting
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Green sand moulding
• Green sand is by far the most diversified moulding
method used in current metal casting operations.
• The green sand process utilises a mould made of
compressed or compacted moist sand packed around
a wood or metal pattern.
• The term "green" denotes the presence of moisture in
the moulding sand, and indicates that the mould is not
baked or dried.
• http://youtu.be/QFLArEHFFHo 4/8 mins
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Sand casting
https://www.youtube.com/watch?v=JwjJ0DlE3fA#action=share
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