SLA - Stereolithography

This technology uses a UV-curing photopolymer resin poured into a container with a transparent base. Underneath the that tank is a light source, such as a laser or, in most newer printers, an LCD screen, which cures the resin. A moving platform is lowered into the resin tank, stopping only at a height equal to the desired layer thickness. The light source then cures the first layer of resin, after which the platform rises a few centimetres and then descends, stopping at the height of the next layer. This process is repeated until the model is finished. 

This technology can produce highly precise parts made from a wide range of materials, including general-purpose resins, composites and elastic materials. However, the parts require additional post-processing steps, such as washing off excess uncured resin and UV curing, which increases the cost and reduces user-friendliness.

FDM - Fused Deposition Modeling

FDM is probably the most common 3D printing technology. It involves melting a filament, or sometimes pellets at larger printers, in a print head, which then extrudes the material in the form of a thin string. The print head then moves around, building up a precise model layer by layer.

It works with thermoplastics, most commonly PLA, which is a rigid material that is easy to use, but has less heat- and impact-resistance. There are other materials available with higher strength, heat or impact resistance, such as PETG, ABS, PA and also some glass- or carbon-filled plastics, as well as elastic ones like TPU. Stronger materials usually require higher print temperatures and are more difficult to print.

FDM prints generally require less post-processing. Usually, this just involves removing support structures, which can be done in a matter of seconds if the structures are well designed.

Cleaning

With FDM, the first is removing the supports and sanding down the surface if necessary.

SLA, on the other hand, is trickier, because the parts are covered in uncured resin. To remove this, the parts need to be thoroughly washed in a solvent, such as IPA. The solvent is then exposed to UV light to cure the dissolved resin. The resulting slurry is then filtered and safely disposed of. This makes it possible to reuse the cleaning agent for longer, making a smaller environmental impact.

The clean parts are then left in a UV curing chamber to solidify and develop their final strength and properties. Similar to FDM, the supports are removed and the surfaces sanded if needed.

From this point, the prints are processed in the same way for both technologies.