Stereolithography
Stereolithography, also known as 3-D layering or 3-D printing, allows you to create
solid, plastic, three-dimensional (3-D) objects from CAD drawings in a matter of
hours. Whether you are a mechanical engineer wanting to verify the fit of a part
or an inventor looking to create a plastic prototype of an invention, stereolithography
gives you a fast, easy way to turn CAD drawings into real objects.
3-D printing is a very good example of the age we live in. In the past, it could
conceivably take months to prototype a part -- today you can do it hours. If you
can dream up a product, you can hold a working model in your hands two days later!
The Stereolithography Machine
PT CAM uses a stereolithography machine produced by
3-D Systems and shown here:
This machine has four important parts:
- A tank filled with several gallons of liquid photopolymer. The photopolymer is a
clear, liquid plastic.
- A perforated platform immersed in the tank. The platform can move up and down in
the tank as the printing process proceeds.
- An ultraviolet laser
- A computer that drives the laser and the platform.
The photopolymer is sensitive to ultraviolet light, so when the laser touches the
photopolymer, the polymer hardens.
If you stand next to the stereolithograph apparatus (SLA), you can actually see
the laser as it builds each layer.
This short MPEG file lets you see the laser building a small section of
a model.
The Stereolithography Process
The basic printing process goes like this:
- You create a 3-D model of your object in a CAD program
- A piece of software chops your CAD model up into thin layers - typically five to
10 layers/millimeter
- The 3-D printer's laser "paints" one of the layers, exposing the liquid
plastic in the tank and hardening it
- The platform drops down into the tank a fraction of a millimeter and the laser paints
the next layer
- This process repeats, layer by layer, until your model is complete
This is not a particularly quick process. Depending on the size and number of objects
being created, the laser might take a minute or two for each layer. A typical run
might take six to 12 hours. Runs over several days are possible for large objects
(maximum size for the machine shown above is an object 10 inches (25 cm) in three
dimensions).
You start by creating a 3-D design for your object in a CAD program. This design
is tweaked before building with supports that raise it up off the tray slightly
and with any internal bracing that is required during building. The SLA then renders
the object automatically (and unattended). When the process is complete, the SLA
raises the platform and you end up with your 3-D object. If the object is small,
you can produce several of them at the same time if you like. They all sit next
to each other on the tray.
The following photo shows a tray after building is complete, with several identical
objects that were produced simultaneously:
Once the run is complete, you rinse the objects with a solvent and then "bake"
them in an ultraviolet oven that thoroughly cures the plastic.
What You Can Create with Stereolithography
Stereolithography allows you to create almost any 3-D shape you can imagine. If
you can get it into a CAD program, you can probably create it. The only caveat is
the need for structural integrity during the building process. In some cases, you
need to add internal bracing to a design so that it does not collapse during the
printing or curing phases.
The photo below shows you a typical object that has been created at PT CAM. The
piece is lightweight and has the strength of polystyrene plastic. You can mount
it, drill it, etc., so you can try it out in actual use. For example, a chair manufacturer
will produce different arm rest shapes using stereolithography and try them out
on actual chairs to see how they feel.
This is a close-up of an engine manifold:
For more detail on the manifold, see
this short video.