Vacuum Forming Plastic

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Vacuum Forming Plastic
Vacuum Forming is an industrial technique which
may be used for batch production or mass
production. A sheet of thermoplastic held by the
use of toggle clamps is heated until the plastic
becomes malleable (soft and flexible). The air
is then sucked out from underneath the plastic
using a vacuum pump. Atmospheric pressure
presses down on top of the plastic sheet which in
turn presses down onto a mould or pattern.The
plastic sheet takes the shape of the mould.This
process enables thermoplastics to be formed into
complicated shapes such as packaging, storage
trays and seed trays.
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The Vacuum forming machine
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Moulds
The Plastic Vacuum formed shape will only ever be
as good as the mould or pattern. It is very
important that the mould is correctly made. The
mould may be made from plywood, hardened clay or
m.d.f. In Industry the mould may be made from
steel or lead. A Steel mould will tend to last
longer than a wooden mould. Stages of making the
mould.1. The sides of the mould must slope
slightly. This is to allow the plastic shape to
be removed after vacuum forming. These are called
Draft Angles.2. The mould must be well sanded,
polished or smoothed depending on the materials
used. Any surface detail which is left on the
mould will be transferred to the plastic
product.3. The mould may have small drill holes
in it to allow the air to be easily sucked
through it by the vacuum pump. This will create
an improved definition or shape. These holes are
called Vent Holes. These holes also prevent small
pockets of air being trapped when the sheet
forms.4. The mould must not be too deep,
otherwise the excess plastic (polystyrene) will
stick together at the corners. This is called
WEBBING. This also affects the thickness of the
sheet on the vertical surfaces as it is drawn
down.
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Examples of vacuum formed trays
A vacuum forming mould.
Note holes to let air out
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The moulds key points
Moulds are usually made from wood or metalwe use
MDF (medium density fibreboard) It is easy to cut
and shape with a file and glass paper Always make
sure that the sides slope so that the mould can
drop out after you have vacuum formed your shape.
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Ideal mould shape
Shapes you can and can't mould... Almost any
shape can be produced, but not necessarily in one
piece. It must be possible to release the plastic
from the mould. This generally means no undercuts
in the shape of the mould parallel vertical
faces can also cause difficulties.
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Bad moulds
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Things that can go wrong
When the plastic is moulded over a tall, steep
shape, depending on the plastic being used, it
can form curtain-like forms. The pic shows it
better than words...
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Step 1
Put the former in the vacuum forming machine and
clamp the plastic into position.
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Step 2
Heat the plastic until it softens to a 'rubber
like' state.
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Step 3
Remove the heat and raise the former into the
softened plastic.
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Step 4
Turn on the vacuum. The plastic will be drawn
around the shape of the former.
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Step 5
When cooled, unclamp the plastic and remove the
former. Trim to the required size and shape
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How it works the movie!Steps 1-5
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Using your design

• Produce a flow chart that illustrates the step by
  step process of manufacturing the mould you will
  need.
• Identify the changes you have had to make to your
  design to make it work with this process.