What is SLA 3D printing?

In this introduction to Stereolithography (SLA) we cover the basic principles of the process that are key to determine whether it is suitable for a specific application. After reading this article you will be familiar with all the important aspects of SLA 3D printing. 

What is stereolithography?

3D printing technology tree highlighting SLA

Stereolithography (SLA) is an additive manufacturing process that belongs to the vat photopolymerization family. Also known as resin 3D printing , there are three main 3D printing technologies associated with vat polymerization: SLA, DLP, and LCD. The three technologies all use a light source to cure a photopolymer reason but with the following differences:

Stereolithography (SLA) uses UV lasers as a light source to selectively cure a polymer resin.

  • Digital light processing (DLP) uses a digital projector as a UV light source to cure a layer of resin.

  • Liquid crystal display (LCD) uses an LCD display module to project specific light patterns.

SLA is one of the most widely used vat photopolymerization technologies. It is used to create objects by selectively curing a polymer resin, layer by layer, using an ultraviolet (UV) laser beam. The materials used in SLA are photosensitive thermoset polymers that come in a liquid form.

How does stereolithography work ?

  1. SLA 3D printing works by first positioning the build platform in the tank of liquid photopolymer, at a distance of one layer height for the surface of the liquid.

  2. A UV laser creates the next layer by selectively curing and solidifying the photopolymer resin.

  3. During the solidification part of the photopolymerization process, the monomer carbon chains that compose the liquid resin are activated by the light of the UV laser and become solid, creating strong unbreakable bonds between each other.

  4. The laser beam is focused in a predetermined path using a set of mirrors, called galvos. The whole cross-sectional area of the model is scanned, so the produced part is fully solid.

  5. After printing, the part is in a not-fully-cured state. It requires further post-processing under UV light if very high mechanical and thermal properties are required.

The photopolymerization process is irreversible and there is no way to convert the SLA parts back to their liquid form. Heating these SLA parts will cause them to burn instead of melting. This is because the materials that are produced with SLA are made of thermoset polymers, as opposed to the thermoplastics that fused deposition modeling (FDM) uses.

Schematic of SLA printer
Schematic of SLA printer


What are the advantages of SLA 3D printing?

  • SLA can produce parts with very high dimensional accuracy and with intricate details.

  • SLA parts have a very smooth surface finish, making them ideal for visual prototypes.

  • Speciality SLA materials are available, such as clear, flexible and castable resins.

What are the disadvantages of SLA 3D printing?

  • SLA parts are generally brittle and not suitable for functional prototypes. 

  • The mechanical properties and visual appearance of SLA parts will degrade over time when the parts are exposed to sunlight.

  • Support structures are always required and post-processing is necessary to remove the visual marks left on the SLA part.

Schematic of SLA printer
Schematic of SLA printer

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