Step 4
At this point the oven is warming up. It usually takes about 2-3 minutes for the
initial warm-up after that you can form parts in a series with no delay. After the
oven has warmed up bring the frame down (half way) open the thumb screws
and the frame, place the plastic on the bottom frame and tighten the thumb
screws. The frame is adjustable in the rear to accommodate different plastic
thicknesses, simply loosen the screws in the back (
lower screws
) and adjust.
Bring the frame up all the way to the oven (make sure it is straight so it heats up
evenly. The sag rate will depend on the plastic thickness/type, mold shape, mold
height, but 2-3 inches is a good starting point (more for taller molds). If you are
using thicker plastics or other forms of plastics that are harder you may need to
heat the plastic longer and the opposite for thinner plastics.
The key thing to remember is that the plastic on the frame should be heated
evenly including all four corners
. You can use a rounded stick or pencil to
touch the plastic momentarily when it
’s sagging to get a feel of how you are doing
on the corners. The more the plastic is heated the more detail will be transferred
to the finished part, but this must be balanced so webbing does not occur. If
webbing occurs either the plastic is too thin (try thicker plastic), you are trying to
form multiple awkward objects at once, plastic has stretched too much or you
need to raise the mold. This can be accomplished by cutting a piece of wood 2-3
inches high depending on the severity of the web slightly larger or same size as
your mold (follow the contour of the mold) and placing it underneath the mold.
You may need to drill some holes in the spacer you created for suction. This will
cause the webbing to occur below the mold where it
’s not important in some
cases. It is always better to keep the mold at room temperature or warmer since
a cold mold will cause the hot plastic to cool faster as it touches it (especially
when using thinner plastics). You can place your mold(s) on the platen while the
machine is warming up to keep them warm.
Step 5
At this point turn on the suction source, and bring the frame down (make sure
you bring it down all the way so the hot plastic makes contact with the frame and
acts as a gasket). This movement should be quick and you should bring it down
in a way that you come down level on all sides. As soon as the hot plastic goes
over the mold and makes good contact with the forming area it will be sucked
over the mold. Turn your suction source off once the plastic has cooled (you can
leave the heater on if you are going to form more parts). The distance between
the oven and the platen will not allow the plastic to get soft again. If you lift the
plastic early (while still soft) it may deform. If you have trouble getting your mold
