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How Stereolithography 3-D Layering WorksbyMarshall Brain

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Inside this Article

1. Introduction to How Stereolithography (3-D Layering) Works2. The Stereolithography Machine3. The Stereolithography Process4. What You Can Create with Stereolithography5. Costs of Stereolithography6. Lots More Information7. See more

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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 mechanicalengineer wanting to verify the fit of a part or an inventor looking to create a plastic prototype of aninvention, 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! In this edition ofHow Stuff Works, we will take a tour of

thestereolithography service bureau at PT CAM (Piedmont Triad Center for Advanced Manufacturing)

so that you can understand everything involved and see some actual 3-D models that this technology has

produced!

The Stereolithography Machine

PT CAM uses a stereolithography machine produced by3-D Systemsand shown here:

Stereolithography Image Gallery
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3-D Systems stereolithography machine at PT CAM.

See morepictures of stereolithography.

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
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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 10inches (25 cm) in three dimensions).

A typical CAD drawing ready to be rendered on the 3-D printer.This particular piece is a plastic money clip that PT CAM givesaway to visitors. Note the supports (in red) that separate the

money clip from the tray and support it is it is being built. About50 of these money clips can be created in a single run.

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.


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The platform in the tank of photopolymer at the beginning of a

print run.

The following photo shows a tray after building is complete, with several identical objects that were

produced simultaneously:

The platform at the end of a print run, shown here withseveral identical objects.

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.


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The ultraviolet "oven" used to cure completed objects.

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:


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For more detail on the manifold, seethis short video.

Costs of Stereolithography

Stereolithography is not an inexpensive process. The machines themselves usually cost in excess of

$250,000. They have to be vented because of fumes created by the polymer and the solvents. The

polymer itself is extremely expensive. CibaTool SL5170 resin, a common photopolymer used in

stereolithography, typically costs about $800/gallon. For these reasons, it is uncommon to find

stereolithography machines anywhere but in large companies. However, there are service bureaus that can make the advantages of stereolithography available to

smaller shops and individuals. For example,PT CAMwill do stereolithography for $55/hour, as well as

allowing companies to purchase blocks of time for as low as $30/hour. That's not cheap, but compared to

purchasing your own SLA and resin or having parts machined, it is a real bargain. You can e-mail your

CAD design to PT CAM and, in many cases, get your parts shipped back to you in a day or two. The

short cycle time is one of the most appealing things about stereolithography!Special thanks to Joel Leonard, Jerry Watkins and Steve Oneyear for their help in creating this article!
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