毕业论文英文版
北京高考分数-
辽宁科技大学本科生毕业设计
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The Basic of Injection Molding Machine
Injection
molding
is
a
manufacturing
process
for
producing
parts
from
both
thermoplastic and thermosetting plastic
materials. Material is fed into a heated barrel,
mixed,
and
forced
into
a
mold
cavity
where
it
cools
and
hardens
to
the
configuration
of
the
mold
cavity.
After a product is designed, usually by an
industrial designer or an engineer, molds are
made
by
a
moldmaker
(or
toolmaker)
from
metal,
usually
either
steel
or
aluminium,
and
precision-machined to form the features
of the desired part. Injection molding is widely
used
for manufacturing a variety of
parts, from the smallest component to entire body
panels of car
History
In
1868 John Wesley Hyatt developed a plastic
material he named Celluloid which had
been invented in 1851 by Alexander
Parks. Hyatt improved it so that it could be
processed
into finished form. In 1872
John, with his brother Isaiah, patented the first
injection molding
machine.
This
machine
was
relatively
simple
compared
to
the
machines
we
use
today.
It
basically worked like a large
hypodermic needle injecting plastic through a
heated cylinder
into a mold. The
industry progressed slowly over the years
producing products such as collar
stays, buttons, and hair combs until it
exploded in the 1940s because World War 2 created
a
huge demand for inexpensive, mass-
produced products. In 1946 James Hendry built the
first
screw injection machine. This
machine allowed material to be mixed before
injection, which
meant
colored
plastic
or
recycled
plastic
could
be
added
to
the
virgin
material
and
mixed
thoroughly
before
being
injected.
Today
screw
injection
machines
account
for
95%
of
all
injection
machines.
The
industry
has
evolved
over
the
years
from
producing
combs
and
buttons
to
producing
a
vast
array
of
products
for
many
industries
including
automotive,
medical,
aerospace, consumer, toys, plumbing, packaging,
and construction.
Applications
Injection molding is used to create
many things such as milk cartons, containers,
bottle
caps, automotive dashboards,
pocket combs, and most other plastic products
available today.
辽宁科技大学本科生毕业设计
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Injection molding is the most common
method of part manufacturing. It is ideal for
producing
high volumes of the same
object. Some advantages of injection molding are
high production
rates,
high
tolerances
are
repeatable,
wide
range
of
materials
can
be
used,
low
labour
cost,
minimal scrap losses,
and little need to finish parts after molding.
Some disadvantages of this
process are
expensive equipment investment, running costs may
be high, and parts must be
designed
with molding consideration.
Design Considerations for the Process
It is important when designing products
for injection molding that you consider how they
will be formed in the machine, how they
will be taken out of the machine, and the
structure of
the final product. Some
important guidelines are:
1. Use
approximately uniform wall thicknesses throughout
your designs.
2. Keep walls thin -
typically between 1/32
reduces cost by
minimizing use of material. Thin walls also reduce
problems with material
shrinkage.
Although some unevenness will occur due to
shrinkage, walls as thick as 1/5
be
used. Keep wall thickness at least wall length /
50..
3. To strengthen
parts, instead of using thicker walls, use
additional structures such as ribs.
Use
fillets at the base of ribs..
4. Round
corners and edges wherever possible
5.
Lighter colors hide flow patterns better than dark
colors.
6. Keep holes at least
.015
Equipment
Injection
molding machines consist of a material hopper, an
injection ram or screw-type
plunger,
and a heating unit. They are also known as
presses, they hold the molds in which the
components
are
shaped.
Presses
are
rated
by
tonnage,
which
expresses
the
amount
of
clamping
force
that
the
machine
can
exert.
This
force
keeps
the
mold
closed
during
the
辽宁科技大学本科生毕业设计
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injection process. Tonnage can vary
from less than 5 tons to 6000 tons, with the
higher figures
used
in
comparatively
few
manufacturing
operations.
The
total
clamp
force
needed
is
determined by the projected area of the
part being molded. This projected area is
multiplied
by a clamp force of from 2
to 8 tons for each square inch of the projected
areas. As a rule of
thumb, 4 or 5
tons/in
2
can be used for
most products. If the plastic material is very
stiff, it will
require more injection
pressure to fill the mold, thus more clamp tonnage
to hold the mold
closed. The required
force can also be determined by the material used
and the size of the part,
and larger
parts require higher clamping force.
Power Requirements
The power required for this process of
injection molding depends on many things and
varies
materials
used.
Manufacturing
Processes
Reference
Guide
states
that
the
power
requirements
depend
on
material's
specific
gravity,
melting
point,
thermal
conductivity,
part size, and molding rate.
Cost
The
cost
of
manufacturing
molds
depends
on
a
very
large
set
of
factors
ranging
from
number
of
cavities,
size
of
the
parts
,
complexity
of
the
pieces,
expected
tool
longevity,
surface finishes and many others. The
initial cost is great, however the piece part cost
is low,
so with greater quantities the
overall price decreases.
n
Effects on the material
properties
The
mechanical
properties
of
a
part
are
usually
little
effected.
Some
parts
can
have
internal
stresses
in
them.
This
is
one
of
the
reasons
why
it's
good
to
have
uniform
wall
thickness
when
molding.
One
of
the
physical
property
changes
is
shrinkage.
A
permanent
chemical
property
change
is
the
material
thermoset,
which
can't
be
remelted
to
be
injected