- [Instructor] Let's take a look at materials
commonly used in prototyping and rapid production.
I'll define the main material types of polymers,
thermoplastics, and elastomers
with example materials, key features, and differences.
Lastly, I'll talk about some of the different forms
these materials can come in,
as that affects which processes they can be used in.
For better or for worse,
there's a ton of crossover between categories
through the shared nature of formable materials.
So there are crossover exceptions in almost every category.
As you can see, polymer is divided first
into thermoplastics and thermosetting categories,
which do not intersect.
And elastomers are generally thermoset,
but some are thermoplastic.
This'll make more sense in a minute.
I promise I'll only talk about the molecular chemistry
of materials for this first differentiation.
The rest is qualitative comparison.
Polymers are the overall main category
of materials that exhibit plastic
or formable characteristics.
It's their unique structure that makes them special.
Polymers consist of extremely long molecular chains
that are represented with overlapping atom loops
and are the basis for the rest of the materials
described in this chapter.
Thermoplastics are a category of polymer
that can be heated and reformed multiple times.
They have high plasticity in their ability
to melt, flow, bend, and repeat.
Remember our ice cube example?
ABS is a common synthetic thermoplastic
used for consumer goods and automotive parts,
which exhibits high impact resistance and durability.
Thermosets are the other main category of polymers,
which have extra toughness due to the fact
that they go through a chemical reaction
called cross-linking where it cures
into its final structure.
The change creates strong bonds that don't melt.
And remember our egg example?
They're usually very heat-resistant,
though at a certain limit they start
to degrade instead of melting.
Melamine and polyester resins are common thermosets
used for sheet applications, like counter surfaces.
They hold up for a very long time.
Elastomers are polymers that have both
formable plastic characteristics
and elastic or squishy characteristics,
which means that when force is applied
they can stretch or compress.
And when force is released,
they can spring back into shape.
Elastomers include materials like silicone,
natural gum tree rubber, and some foams.
Now that the categories have been established,
it's time to talk about the different forms
these materials can come in.
With thermoset materials, the isolated components
are often kept in a liquid form
until they are needed for combination and molding.
With thermoplastic materials, the plastic
is melted with heat in preparation
for extrusion or injection molding.
Pellets are one of the most common forms of thermoplastics
prior to injection or extrusion.
Pellets are useful because they're reasonably
easy to measure and because their high surface area
helps them melt quickly and completely
for pressurized injection.
Powders are finely ground plastics,
generally thermoplastics, using hot mold melting processes,
like rotational molding.
Because powders have an extremely high surface area,
this enables them to melt extremely quickly
and flow into all of the surface details of the mold.
Extrusions are also generally thermoplastics
that have been melted and pushed out of a machine
in a solid cross section.
One of the common extrusions you might have
already run into are filaments.
Filaments are extrusions with round profiles
using 3D printing, kept solid on spools
until heated for re-extrusion to 3D print your part.
Putty charges are commonly thermoset materials
placed in heated molds for thermo-forming.
The material is already in
a semi-solid clay-like consistency.
Other materials in this category
would include both naturally occurring
and synthetic clay and waxes used to create master forms.
Some car companies still use clay sculpting techniques
to help define their designs.
Foams are special because of the way that they're made.
Air is introduced, either by mixing components
that create a chemical reaction,
or by being frothed up mechanically
with an inert gas to encourage bubble formation.
Foams could be made from either
thermoset or thermoplastic materials
to create strong and rigid foams or soft and pliable ones.
An interesting thermoset elastomer foam
is polyurethane foam which combines
highly squishy pliability with high toughness.
This addition of air creates a great application
for flotation devices, impact,
and sound insulation due to its low density.
While this definitely helps overview
the different categories and forms materials can come in,
you'll have to do some exploring on your own
to find the best materials for your project.
Different projects have different needs.
So first establish what you need
and want your part to do
and then research the best material to fit those needs.