CHAPTER 1
OVERVIEW OF CASTING
TECHNOLOGY
Ass.Pr.Dr. Nguyen Ngoc Ha
1. CASTING OF METAL
• Metal-Casting Processes
– First casting were made
during 4000 – 3000 BC
– In time many casting
processes have been
developed
– Many parts can be made
from castings
• Engine blocks
• Cameras
• Gun barrels
• Cook ware
• Etc
Ancient Greece; bronze
statue casting circa 450BC
Iron works in early
Europe,
e.g. cast iron
cannons from
England circa
1543
1. CASTING OF METAL
• Process
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in which molten metal flows by
gravity or other force into a mold where it
solidifies in the shape of the mold 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 mold
3. Let it freeze
Example – Sand Casting
Example – Die Casting
Example – Investment Casting
Evaporative Pattern Casting
(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
General characteristics of casting processes
2. 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
3. DISADVANTAGES OF CASTING
• Different disadvantages for different casting
processes:
– 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
4. 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, pump housings
• Small parts
– Dental crowns, jewelry, small statues, frying pans
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) 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.
5. THE MOLD IN CASTING
• Contains cavity whose geometry determines
part shape
– Actual size and shape of cavity must be slightly enlarged
to allow for shrinkage of metal during solidification and
cooling
– Molds are made of a variety of materials, including sand,
plaster, ceramic, and metal
Open Molds and Closed Molds
• Two forms of mold: (a) open mold and (b)
closed mold for more complex mold geometry
with gating system leading into the cavity
Two Categories of Casting Processes
1. Expendable mold processes – use an
expendable mold which must be destroyed to
remove casting
– Mold materials: sand, plaster, and similar materials,
plus binders
2. Permanent mold processes – use a
permanent mold which can be used to
produce many castings
– Made of metal (or, less commonly, a ceramic refractory
material
Two Categories of Casting Processes
6. CASTING TERMINOLOGY
6. CASTING TERMINOLOGY
• Flask
The box containing the mold
• Cope
The top half of any part of a 2-part mold
• Drag
The bottom half of any part of a 2-part mold
• Core
A shape inserted into the mold to form internal
cavities
• Core Print
A region used to support the core
6. CASTING TERMINOLOGY
• Mold Cavity
The hollow mold area in which metal solidifies into the
part
• Riser
An extra cavity to store additional metal to prevent
shrinkage
• Gating System
Channels used to deliver metal into the mold cavity
• Pouring Cup
The part of the gating system that receives poured metal
• Sprue
Vertical channel
6. CASTING TERMINOLOGY
• Runners
Horizontal channels
• Parting Line / Parting Surface
Interface that separates the cope and drag of a 2-part
mold
• Draft
Taper on a pattern or casting that allows removal from
the mold
• Core Box
Mold or die used to produce cores
• Casting
The process and product of solidifying metal in a mold
7. STEPS IN CASTING
1. Prepare mold for pour
2. Pour molten metal into sand mold
3. Allow metal to solidify
4. Break up the mold to remove casting
5. Clean and inspect casting
6. Heat treatment of casting is sometimes
required to improve metallurgical properties
7. STEPS IN CASTING
8. TRENDS
1. Continuing mechanization & automation of
the casting process
2. Increasing demand for high-quality castings
3. Computer-aided design
4. Rapid (free-form) pattern making
Computer modeling of casting processes
• Rapid advances in computers and modeling analysis led
innovations in modeling different aspects of casting
including: fluid flow, heat transfer, and microstructures
developed during solidification; under various casting-
process conditions.
• Specifically, software may provide:
Modeling fluid flow in molds (Bernoulli’s and
continuity). Predict velocity and pressure of the
molten metal in the gating system all the way into
the mold cavity.
Modeling of heat transfer in casting.
Fluid flow and heat transfer (with surface conditions,
thermal properties of materials) are coupled.
Modeling the development of microstructure in
casting.
Computer modeling of casting processes
• The benefits of such user-friendly software are to
increase productivity, improve quality, and easily
plan and estimate cost. Also quicker response to
design changes.
• Several commercial software programs now are
available for modeling of casting processes:
1. Magmasoft,
2. ProCast,
3. Solidia, and
4. AFSsolid.
9. ECONOMICS OF CASTING
• The cost of the cast part (unit cost) depends
on several factors: including materials, tooling,
equipment, and labor.
• Preparations for casting a product include the
production of molds and dies that require raw
materials, time, and effort – all of which also
influence product cost.
Cost Characteristics of Casting
Cost Characteristics of Casting
• As shown in table 12.6, relatively little cost is
involved in molds for sand casting. On the
other hand, molds for various processes and
die-casting dies require expensive materials
and a great deal of preparation.
• There are also major costs involved in making
patterns for casting.
• Costs also are involved in melting and pouring
the molten metal into molds and in heat
treating, cleaning, and inspecting the casting.
Cost Characteristics of Casting
• Heat treatment in an important part of the
production of many alloys groups (especially
ferrous castings) and may be necessary to
produce improved mechanical properties.
• The equipment cost per casting will decrease as
the number of parts cast increase. Sustained
high-production rates, therefore, can justify the
high cost of dies and machinery.
• However, if the demand is relatively small, the
cost-per-casting increases rapidly. It then
becomes more economical to manufacture the
parts by sand casting.
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