- [Instructor] Press molding, or compression molding,
is a manufacturing version of making waffles.
Material is introduced to a heated mold,
and then compressed with pressure,
squeezing out excess material along the parting line.
Often used with thermoset materials,
the heat in the mold helps cure
the material into its final form.
Both thermoplastic and thermoset plastics
can be used in this process,
depending on the end use of the part.
A common use example of press molding
would be the outsoles for shoes or rubber rainboots.
I designed this trivet with this method
of manufacture in mind.
If you look at this in a cut through,
you can see there are significant
thickness variations between the thickest
and the thinnest parts of the design.
Because the silicone is a thermoset,
it won't melt under the heat.
You can get some depth out of press molding with open shapes
but this process is best suited for larger flat shapes.
You might choose press molding
when your project start to exceed
sizes suitable for injection molding,
or because the machinery costs less.
You can even have variable wall thicknesses
with this method because the parts are generally thicker,
and solid overall.
Since the compression is the only force
introduced to the material,
it lacks some of the integrated stresses,
and results in a relatively stable part.
The mold halves no longer have to be cavity and core.
They could both be cavity sections for thick parts.
Keep in mind that compression molding
also has ejector pins.
So this will affect your design.
Because of the squeezing action of this method,
flash material can come outta the sides
along the parting, and that will need
to be trimmed off later.
Of note, compression molding was the original method
to form big light products.
And is well suited to molding fiber embedded,
or composite materials.
Because composite materials often don't flow as easily,
compression molding can make accurate parts
with chopped synthetic or organic fibers
embedded in the plastic.