- [Narrator] As previously discussed,
CNC is a versatile manufacturing method.
It can make extremely precise final parts
and is a method used to create most factory
plastic forming dies, out of metal.
Another capability of CNC is making volumetric,
one-sided forms for heat-forming sheet plastic.
Vacuum forming is a process,
in which flat, extruded sheet plastic
is shaped over a master form, with heat and suction.
The plastic used in this process can vary,
in thickness and texture, but calls for thermoplastic sheet,
as it may need to be heated and formed multiple times.
There are a few steps to vacuum forming.
First, the sheet is clamped into a sturdy frame,
to keep it square, and is then heated with coils,
by an oven, until it reaches
a right temperature and pliability.
Once the sheet has reached the specified softness and sag,
it will be immediately pulled over the form,
capturing an impression of the detail and allowed to cool.
After the plastic has cooled enough,
to retain the shape of the form, the vacuum pressure ceases,
and the new part in the sheet,
is removed from the vacuum table.
And the excess is trimmed off.
Some facilities recycle these discarded plastic scraps
and recycle them back into the sheet extruding process.
Because of the stretching involved in this process,
the sheet does not maintain perfectly even thickness.
The interior of the part,
will approximately match the exterior
of the geometry of the master form.
This method is not as precise as some of the others
but is relatively cheap
and might be the right method for your project.
This is a technique commonly used
for thin, translucent plastic,
in the application of blister packaging,
divider trays and pills.
Because the sheet material is often thin,
you'll need to watch out for aggressively, pointy geometry,
which can tear the sheet.
The application of fillets is your friend.
Let's say I wanna make a form,
for decorative ceiling panels.
The material used for these master forms
should be inert to heat and not melt on contact.
You can make forms out of any number of materials:
wood, plywood, aluminum, high-density foams
and composite stock, like MDF or LDF.
The advantage of having porous or perforated material
is that the vacuum can pull,
not just around your form, but through it.
And release of the vacuum pressure
will aid in the removal of the formed sheet.
There are, however, restrictions
in the usage of this method.
Too much additional height can result in tearing,
as there are limits to the plastic's ability to stretch.
Other problems can arise, in the form of webbing,
where the walls are too high and straight,
and the material cannot pull down and around this.
It sometimes folds together.
Depending on the thickness and size of your sheet,
taller forms can be made, but every inch,
above the support platform,
makes it harder and more complex to form.
It's not recommended to try and vacuum form geometry
with severe undercuts, sharp sharps,
or if you need perfectly uniform parts.
You can have parts with holes,
but they will have to be cut out of your part,
after the molding process.