How Stereolithography Works: A 3D Printing Process

PT CAM uses a stereolithography machine produced by 3D Systems. This machine has four important parts:

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.

SLA Materials

A few primary materials include photosensitive polymers and support structures, which support overhanging features but do not pass the post-processing. Secondary and specialized materials are high heat deflection and high-temperature resins, both of which can withstand high heat deflection temperatures, and flexible and durable resins fit for bending and flexing.

The core of SLA printing involves a laser beam precisely directed by a light-emitting device to cure the polymer resin in a resin tank. The SLA printing process goes something like this:

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 6 to 12 hours. Runs over several days are possible for large objects (maximum size for the relatively old machine shown above is an object 10 inches, or 25 centimeters, in three dimensions).

You start by creating a 3D 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 3D object. If the object is small, you can produce several of them simultaneously 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 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.

Advantages of Using SLA Technology

SLA technology offers several benefits over traditional manufacturing methods like injection molding and fused deposition modeling. It is capable of producing parts with smooth surface finishes, fine features, and high complexity without the need for multiple tools or molds.

Stereolithography allows you to create almost any 3D 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 on this page shows you a typical object that was created at PT CAM. The piece is lightweight and has the strength of polystyrene plastic. Since you can mount and drill pieces, you can try it out in actual use.

For example, a chair manufacturer will produce different armrest shapes using stereolithography and try them out on actual chairs to see how they feel.

Stereolithography is not an inexpensive process. The machines once cost in excess of $250,000 and still get up to tens of thousands of dollars (but you can find desktop SLA printers for much less). You also need to vent them because of the fumes the polymer and the solvents create.

The polymer is extremely expensive as well. CibaTool SL5170 resin, a common photopolymer used in stereolithography, cost about $800/gallon when we visited PT CAM. For these reasons, it is uncommon to find professional 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. It's still not cheap, but compared to purchasing your own SLA and resin or having parts machined, it is a real bargain.

Special thanks to Joel Leonard, Jerry Watkins and Steve Oneyear for their help in creating this article!

We updated this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.