Ethiopian Technical University
Faculty of Mechanical Technology-department of Manufacturing
Technology
Advanced Metal Casting Technology (MAT515)
Open Book Test One
By: Bizuayehu Tadesse Azene
ID.No. MTR/489/13 Section 1
Submitted To Instructor: Dr. Asmamaw Tegegne (PhD)
June 2021
Addis Ababa Ethiopia
Questions
1. List down the Following Metals according To Their Cast ability And Reason out Your Answer
in Detail. Metals: stainless Steel, Zinc, High Carbon Steel, Gray Cast Iron, Brass and
Aluminum Alloys
2. Given Are Sand Casting, Centrifugal Casting, Squeeze Casting, Die Casting, Shell Casting,
Investment Casting. List Down According To Their Processing Cost, precision, Range Of
Production, Materials to Be Cast, Skill Required. Resean Out Your Answer In Detail
1
Answer
1. Gray Cast Iron
Castings of gray cast iron have relatively few shrinkage cavities and low porosity. Various forms
of gray cast iron are ferritic, pearlitic, and martensitic. Because of differences in their structures,
each type has different properties. Typical uses of gray cast iron are in engine blocks, electromotor
housings, pipes, and wear surfaces for machines. Also, its high damping capacity has made gray
iron a common material for machine-tool bases. Gray cast irons are specified by a two-digit
ASTM designation. For example, class 20 specifies that the material must have a minimum tensile
strength of 20 ksi (140 MPa).
2. Zinc
Zinc based Alloys. A low-melting-point alloy group, zinc-based alloys have good corrosion
resistance, good fluidity, and sufficient strength for structural applications. These alloys
commonly are used in die casting, particularly for parts with thin walls and intricate shapes.
3. Aluminum alloys.
Aluminum alloys have a wide range of mechanical properties, mainly because of various
hardening mechanisms and heat treatments that can be used with them. These alloys have high
electrical conductivity and generally good atmospheric corrosion resistance. However, their
resistance to some acids and all alkalis is poor, and care must be taken to prevent galvanic
corrosion. They are nontoxic, lightweight, and have good machinability. Except for alloys with
silicon, they generally have low resistance to wear and abrasion. Aluminum-based alloys have
numerous applications, including architectural and decorative uses. An increasing trend is their use
in automobiles, for components such as engine blocks, cylinder heads, intake manifolds,
transmission cases, suspension components, wheels and brakes.
4. Brass
Brass is an alloy of copper and zinc, in proportions which can be varied to achieve varying
mechanical, electrical, and chemical properties. ... The composition of brass, generally 66%
copper and 34% zinc, makes it a favorable substitute for copper based jewelry as it exhibits greater
resistance to corrosion.
5. High Carbon Steel
High carbon steel. Because of the high temperatures required to melt steels (up to about 1650°C,
or 3000°F), casting them requires considerable experience. The high temperatures involved
present difficulties in the selection of mold materials, particularly in view of the high reactivity of
steels with oxygen during the melting and pouring of the metal. Steel castings possess properties
that are more uniform (isotropic) than those made by mechanical working processes if welded,
need to be heat treated to restore mechanical properties. Used in equipment for railroads, mining,
chemical plants, oil fields, and heavy constructions.
6. Stainless Steel
Stainless Steels. Casting of stainless steels involves considerations similar to those for steels.
Stainless steels generally have long freezing ranges and high melting temperatures. They can
develop several structures, depending on their composition and processing parameters. Cast
stainless steels are available in various compositions, and they can be heat treated and welded.
Cast stainless-steel products have high heat and corrosion resistance, especially in the chemical
and food industries.
Quotation 2
1. SAND CASTING
Sand casting, the most widely used casting process, utilizes expendable sand molds to form
complex metal parts that can be made of nearly any alloy. Because the sand mold must be
destroyed in order to remove the part, called the casting, sand casting typically has a low
production rate. The sand casting process involves the use of a furnace, metal, pattern, and sand
mold. The metal is melted in the furnace and then ladled and poured into the cavity of the sand
mold, which is formed by the pattern. The sand mold separates along a parting line and the
solidified casting can be removed.
The sand casting process involves the following basic steps:
 Placing a pattern (having the shape of the desired casting) in sand to make an imprint, fit in
the pattern and sand in a gating system,
 Incorporating a gating system,
 remove the pattern,
 Allowing the metal to cool until it solidifies,
 Break the sand mold and remove the casting.
 Removing the casting
Advantages:
I.
Can produce very large parts
II.
Can form complex shapes
III.
Many material options
IV.
Low tooling and equipment cost
V.
Scrap can be recycled
VI.
Short lead time possible
Disadvantages:
I.
Poor material strength
II.
High porosity possible
III.
Poor surface finish and tolerance
IV.
Secondary machining often required
V.
Low production rate
VI.
High labor cost
Figure 1.1 Production steps in a typical sand-casting operation.
Sands
Most sand-casting operations use silica sand (SiO2) as the mold material. Sand is inexpensive and
is suitable as a mold material because of its high-temperature characteristics and high melting
point. There are two general types of sand: naturally bonded (bank sand) and synthetic (lake
sand). Because its composition can be controlled more accurately, synthetic sand is preferred by
most foundries. For proper functioning, mold sand must be clean and preferably new. Several
factors are important in the selection of sand for molds, and certain tradeoffs with respect to
properties are involved. Sand having fine, round grains can be packed closely and, thus, forms a
smooth mold surface. Although fine-grained sand enhances mold strength, the fine grains also
lower mold permeability (where fluids and gases penetrate through pores). Good permeability of
molds and cores allows gases and steam evolved during the casting to escape easily.
2. Shell mold casting
 Shell mold casting process is recent invention in casting techniques for mass production and
smooth surface finish. It was originated in Germany during Second World War. It is also
called as Carning or C process. It consists of making a mold that possesses two or more thin
shells (shell line parts, which are moderately hard and smooth with a texture consisting of
thermosetting resin bonded sands. The shells are 0.3 to 0.6 mm thick and can be handled and
stored. Shell molds are made so that machining parts fit together-easily. They are held using
clamps or adhesive and metal is poured either in a vertical or horizontal position. They are
supported using rocks or mass of bulky permeable material. Thermosetting resin, dry powder
and sand are mixed thoroughly in a muller.
 Complete shell molding casting processes is carried in four stages. In this process a pattern is
placed on a metal plate and it is then coated with a mixture of fine sand and Phenol-resin
(20:1). The pattern is heated first and silicon grease is then sprayed on the heated metal pattern
for easy separation. The pattern is heated to 205 to 230°C and covered with resin bounded
sand. After 30 seconds, a hard layer of sand is formed over pattern. Pattern and shell are heated
and treated in an oven at 315°C for 60 sec. Phenol resin is allowed to set to a specific
thickness.
Figure 1.2 shell mold casting process
Advantages
The main advantages of shell molding are:
 Very suitable for thin sections like petrol engine cylinder.
 Excellent surface finish.
 Good dimensional accuracy of order of 0.002 to 0.003 mm.
 Negligible machining and cleaning cost.
 Occupies less floor space.
 Skill-ness required is less.
 Molds can be stored until required.
 Better quality of casting assured.
 Mass production.
Disadvantages
 Initial cost is high.
 Specialized equipment is required.
 Resin binder is an expensive material.
 Limited for small size.
 Future of shell molding process is very bright.
Applications
 Suitable for production of casting made up of alloys of Al, Cu and ferrous metals
 Bushing
 Valves bodies
 Rocker arms
 Bearing caps
 Brackets
 Gears
3. Investment Casting
The investment-casting process, also called the lost-wax process, was first used during the
period from 4000 to 3000 B.C. Typical parts made are components for office equipment, as well
as mechanical components such as gears, cams, valves, and ratchets. Parts up to 1.5 m (60 in.) in
diameter and weighing as much as 1140 kg (2500 lb.) have been cast successfully by this process.
The term investment derives from the fact that the pattern is invested (surrounded) with the
refractory material. Wax patterns require careful handling because they are not strong enough to
withstand the forces encountered during mold making; however, unlike plastic patterns, wax can
be recovered and reused.
The one-piece mold is dried in air and heated to a temperature of 90° to 175°C (200° to 375°F). It
is held in an inverted position for a few hours to melt out the wax. The mold is then fired to 650°
to 1050°C (1200° to 1900°F) for about four hours (depending on the metal to be cast) to drive off
the water of crystallization (chemically combined water) and to burn off any residual wax. After
the metal has been poured and has solidified, the mold is broken up and the casting is removed.
Figure 1.3 investment-casting (lost-wax) process
Advantages of investment casting:
 Parts of great complexity and intricacy can be cast
 Good surface finish and close dimensional tolerances;
 Few or no finishing operations
 Wax can usually be recovered for reuse
 Additional machining is not normally required - this is a net shape
process
 Wide variety of ferrous and nonferrous metals and alloys.
Disadvantages
 Would add significantly to the total cost of the casting, are required.
 Many processing steps are required
 Relatively expensive process
 Price per unit costs can be high
 One mold per batch
 Less strength than die cast parts
 Process is slow
 More steps are involved in production
4. CENTRIFUGAL CASTING
As its name implies, the centrifugal-casting process utilizes inertial forces (caused by
rotation) to distribute the molten metal into the mold cavities—a method that was first
suggested in the early 1800s
Types of Centrifugal casting processes
There are three types of centrifugal casting
1) True centrifugal casting
2) Semi-centrifugal casting and
3) Centrifuged casting
 True Centrifugal Casting. In true centrifugal casting, hollow cylindrical parts (such as
pipes, gun barrels, bushings, engine-cylinder liners, bearing rings with or without flanges,
and street lampposts) are produced by the technique. In this process, molten metal is
poured into a rotating mold.
 Semi centrifugal Casting. It is similar to true centrifugal casting but only with a
difference that a central core is used to form the inner surface.
This casting process is generally used for articles which are more complicated than those
possible in true centrifugal casting, but are axi-symmetric in nature.
Centrifuging. In centrifuging (also called centrifuge casting), mold cavities of any shape
are placed at a certain distance from the axis of rotation. The molten metal is poured from
the center and is forced into the mold by centrifugal forces .The properties of the castings
can vary by distance from the axis of rotation, as in true centrifugal casting.
Advantages:
 Can form very large parts
 Good mechanical properties
 Good surface finish and accuracy
 Low equipment cost
 Low labor cost
 Little scrap generated
Disadvantages:
 Limited to cylindrical parts
 Secondary machining is often required for inner diameter
 Long lead time possible
5. Die Casting
The die-casting process, developed in the early 1900s, is a further example of permanentmold casting. The European term for this process is pressure die casting and should not be
confused with pressure casting. Typical parts made by die casting are housings, businessmachine and appliance components, hand-tool components, and toys.
Types of die casting machines
There are two basic types of die casting machines:
1- Hot-chamber and
2- Cold- chamber machines.
The hot-chamber process involves the use of a piston, which forces a certain volume of
metal into the die cavity through a gooseneck and nozzle. Pressures range up to 35 MPa
(5000 psi), with an average of about 15 MPa (2000 psi).
The metal is held under pressure until it solidifies in the die. To improve die life and to aid in
rapid metal cooling (thereby reducing cycle time) dies usually are cooled by circulating
water or oil through various passageways in the die block. Low-melting point alloys (such as
zinc, magnesium, tin, and lead) commonly are cast using this process. Cycle times usually
range from 200 to 300 shots (individual injections) per hour for zinc, although very small
components, such as zipper teeth, can be cast at rates of 18,000 shots per hour.
Cold-chamber process molten metal is poured into the injection cylinder (shot chamber).
The chamber is not heated—hence the term cold chamber. The metal is forced into the die
cavity at pressures usually ranging from 20 to 70 MPa (3 to 10 ksi), although they may be as
high as 150 MPa (20 ksi).
Figure 1.4 hot-chamber die-casting process.
The machines may be horizontal or vertical, in which case the shot chamber is vertical.
High-melting-point alloys of aluminum, magnesium, and copper normally are cast using this
method, although other metals (including ferrous metals) also can be cast. Molten-metal
temperatures start at about 600°C (1150°F) for aluminum and some magnesium alloys, and
increase considerably for copper-based and iron-based alloys.
Figure, 1.5 cold- chamber die-casting process.
Advantages
1. It is very quick process
2. It is used for mass production
3. castings produced by this process are greatly improved surface finish
4. Thin section (0.5 mm Zn, 0.8 mm Al and 0.7 mm Mg) can be easily casted
5. Good tolerances
6. Well defined and distinct surface
7. Less nos. of rejections
8. Cost of production is less
9. Process require less space
10. Very economic process
11. Life of die is long
12. All casting has same size and shape.
Disadvantages
6. Cost of die is high.
7. Only thin casting can be produced.
8. Special skill is required.
9. Unless special precautions are adopted for evaluation of air from die-cavity some air is
always entrapped in castings causing porosity.
10. It is not suitable for low production.
Applications
1. Carburetor bodies 2. Hydraulic brake cylinders 3. Refrigeration castings 4. Washing
machine 5. Connecting rods and automotive pistons 6. Oil pump bodies 7. Gears and gear
covers 8. Aircraft and missile castings, and
11. Squeeze Casting
The squeeze-casting Squeeze casting is a combination of casting and forging in which a
molten metal is poured into a preheated die, and the upper die is closed to create the mold
cavity after solidification begins. The pressure applied by the upper die in squeeze casting
causes the metal to completely fill the cavity, resulting in good surface finish and low
shrinkage
Squeeze casting can be used for both ferrous and non-ferrous alloys, but aluminum and
magnesium alloys are the most common due to their lower melting temperatures.
Automotive parts are a common application
The casting operation
The casting operation consists of preheating the die containing the preform typically to
300-400 C. The molten metal is then poured into the die and the punch is driven into the
die cavity at a constant ram speed of about 10 m/s. In most cases the optimum pressure is
20 to 30 Mp. The pressure is maintained during solidification and additional 5-10 minutes
further cooling period. The ram is then withdrawn and the composite ejected.
Two basic forms of the process may be distinguished; depending on natural the pressure is
applied.
i)
the direct squeeze casting mode
ii)
(ii) the indirect squeeze casting mode
Figure 1.6 Squeeze casting Process
ADVANTAGE OF SQUEEZE CASTING
1- Better mechanical properties.
2- Fine structure minimum porosity.
3- Smooth surface.
4- High productivity.
5- Possible application in composite products.
6- Little or no machining required post casting process
LIMITATION OF SQUEEZE CASTING
2- Reduced life of the metallic mold.
3- Need to high accurately control.
4- Costs are very high due to complex tooling.
5- No flexibility as tooling
Summary of Casting Processes
Process
Sand Casting
Centrifugal Casting
Squeeze Casting
Die Casting
Shell Casting
Investment Casting
Advantages
 Almost any metal can be cast; no
limit to part size, shape, or weight;
low tooling cost
 Skill-ness required is less.
 Large cylindrical or tubular parts
with good quality; high production
rate
Limitations
 Some finishing required;
relatively coarse surface finish;
wide tolerances
 Better mechanical properties.
 Fine structure minimum porosity.
Smooth surface.
Excellent dimensional accuracy and
surface
finish; high production rate
Good dimensional accuracy and surface
finish; high production rate
Intricate part shapes; excellent surface
finish and accuracy; almost any metal
can be cast

Expensive equipment; limited
part shape

Skilled workers are required for
operation

Reduced life of the metallic
mold.
Costs are very high due to
complex tooling.
No flexibility as tooling
High die cost; limited part size;
generally
limited to nonferrous metals;
long lead time
Special skill is required.
Part size limited; expensive
patterns and equipment
Skill-ness required is less
Part size limited; expensive
patterns, molds, and labor








General cost chracterctic of casting process
Process
Cost
Production rat
Pieces per hr.
Die
Equipment
Labor
Sand Casting
L
L
L-M
< 20
Centrifugal Casting
M
H
L- M
< 50
Squeeze Casting
H
H
H
Die Casting
H
H
L-M
< 200
Shell Casting
L-M
M-H
L-M
< 50
Investment Casting
M-H
L-M
H
< 1000
L= low M= medium H =high