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Injection
Moulding
Injection
Moulding is a method of producing plastic components whereby
heated, liquid plastic is forced under pressure into a metal
moulding die which has been hollowed to leave a cavity exactly
the shape of the required part. The die is made in two parts
which are held together by a force of up to 650 tonnes during
moulding, and can be separated to allow the finished part
to be removed.
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The
advantages of this method of plastic moulding for the
point-of-sale and display industry are: |
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Economies
of scale can be achieved on longer production runs |
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Very
long tool life |
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Availability
of a large range of suitable materials and colours |
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Close
tolerances in finished part size can be achieved |
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High
production throughput |
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Disadvantages:
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Large
investment in tooling required |
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Higher
cost of tooling modifications |
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Longer
turnaround time on production of tools |
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Inability
to pre-print onto materials prior to moulding |
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Some
restrictions on part design to allow easy removal
from tool |
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Step 1
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Step
1 - click
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Injection
moulding dies are usually cut from solid blocks of hardened
tool steel, although on occasions it is possible to
use aluminium for short life-span tools.
The
dies are built in two halves which when pressed together
seal to form a solid block with a cavity inside the
shape of the required part. A range of machine sizes
is required to cater for the full range of die sizes
and these machines are generally referred to by the
pressure which they are capable of applying to hold
the two halves of the die together.
Active Display Group's capabilities range from 80 tonnes
to 650 tonnes which more than adequately covers the
range of products required for the display industry.
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Step
2
Plastic
granules of the material type and colour required for the
finished part are loaded into a hopper which sits above the
injection moulding machine.
These
granules are fed down into a chamber where they are forced
by a 'screw' type mechanism, through a heater that melts them
into a liquid, and eventually into the cavity within the die
- which the plastic completely fills.
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Step
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Chilled
water is then pumped throughout the body of the die to quickly
cool the molten plastic to a temperature where it will retain
its new shape.
Step
3
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Once
the cooling cycle is complete, the two halves of the
die are separated by hydraulic rams, and the completed
part is removed. It is usually necessary to remove the
stalks of plastic (or 'sprues') formed by the holes
in the die which allow the molten plastic to flow into
the die.
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Step
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