金工实习英文讲义-铸造

Mechanical Engineering Training

Sand Casting

Name:

Student NO.:

Date:

1.

Introduction to Casting

Casting is a manufacturing process by which a liquid material is usually poured into a

mold, which contains a hollow cavity of the desired shape, and then allowed to solidify.

The solidified part is also known as a casting, which is ejected or broken out of the mold to

complete

the

process.

Casting

materials

are

usually

metals

or

various

cold

setting

materials that cure after mixing two or more components together; examples are epoxy,

concrete, plaster and clay. Casting is most often used for making complex shapes that

would be otherwise difficult or uneconomical to make by other methods. Casting is a 6000

year old process. The oldest surviving casting is a copper frog from 3200 BC.

In

this

training

course,

considering

the

availability

of

required

equipment

in

the

training center, we will focus on the training of metal casting methods.

2.

Metal Casting and Its Common Methods

Metal casting is one of the most common casting processes. Metal patterns are more

expensive

but

are

more

dimensionally

stable

and

durable.

Metallic

patterns

are

used

where

repetitive

production

of

castings

is

required

in

large

quantities.

Common

metal

casting methods include Sand Casting, Die Casting and Evaporative- pattern Casting.

Sand Casting

Sand

casting,

also

known

as

sand

molded

casting,

is

a

metal

casting

process

characterized by using sand as the mold material. The term

to

an

object

produced

via

the

sand

casting

process.

Sand

castings

are

produced

in

specialized factories called foundries. Over 70% of all metal castings are produced via a

sand casting process. As the most widely used metal casting methods, it is the main focus

of this training course and will be talked about in detail in the following sections.

Figure 1 Sand Casting

Sand casting is relatively cheap and sufficiently refractory even for steel foundry use.

In addition to the sand, a suitable bonding agent (usually clay) is mixed or occurs with the

sand. The mixture is moistened, typically with water, but sometimes with other substances,

to

develop

strength

and

plasticity

of

the

clay

and

to

make

the

aggregate

suitable

for

molding. The sand is typically contained in a system of frames or mold boxes known as a

1

flask.

The

mold

cavities

and

gate

system

are

created

by

compacting

the

sand

around

models, or patterns, or carved directly into the sand. A demonstration of sand casting is

shown in Figure 1.

Die Casting

Die casting is a metal casting process that is characterized by forcing molten metal

under high pressure into a mold cavity. The mold cavity is created using two hardened tool

steel dies which have been machined into shape and work similarly to an injection mold

during the process. Most die castings are made from non- ferrous metals, specifically zinc,

copper, aluminum, magnesium, lead, pewter and tin based alloys. Depending on the type

of metal being cast, a hot- or cold- chamber machine is used.

The casting equipment and the metal dies represent large capital costs and this tends

to limit the process to high volume production. Manufacture of parts using die casting is

relatively

simple,

involving

only

four

main

steps,

which

keeps

the

incremental

cost

per

item

low.

It

is

especially

suited

for

a

large

quantity

of

small

to

medium

sized

castings,

which

is

why

die

casting

produces

more

castings

than

any

other

casting

process.

Die

castings

are

characterized

by

a

very

good

surface

finish

(by

casting

standards)

and

dimensional consistency.

Figure 2 shows a die casting machine. In later sessions of the training course, you will

have the chance to see the die casting process and make an aluminum model of a fighter

yourself with the machine.

Figure 2 Die Casting Machine

Evaporative-pattern Casting

Evaporative-pattern

casting

is

a

type

of

casting

process

that

uses

a

pattern

made

from a material that will evaporate when the molten metal is poured into the molding cavity.

The most common evaporative- pattern material used is polystyrene foam.

The two major evaporative-pattern casting processes are:

(1)

Lost-foam casting

(2)

Full-mold casting

The main difference is that lost-foam casting uses an unbonded sand and full-mold

casting

uses

a

bonded

sand

(or

green

sand).

Figure

3

shows

patterns

and

according

products made from the patterns in evaporative-pattern casting. Please pay attention to

2