Theory

SLA stands for stereolithography (why stereo? It’s weird I know, also known as vat photopolymerization (photo what?), optical fabrication, photo-solidification, or just resin printing), it exposes photo-sensitive resin to a typically 405nm UV light source, which cures (polymerizes) the liquid resin and produces a solid part.

https://youtu.be/8tn5zA5bNSE

Similar to FDM printing, SLA or resin printing is done in layers as well. A slicer is also used to translate a 3D model to 2D contours, where then a part can be printed layer by layer.

How does it print?

Photo-sensitive resin is poured in a vat/tank, where layers of liquid resin gets solidified/cured onto the build plate. It’s similar to upside-down FDM printing and the build platform drags the printed part out of the pool of resin.

Anatomy

1. Printed part!
2. Resin printing needs support as well! Unlike FDM, however, resin supports are like trees with rods and branches, and the attachment points to parts are often small and pointy. This is to promote breakaway from part and minimize light leakage for better surface finish of part.

1. A tank of liquid resin acting as a reservoir that also submerges the part, keeping material available for exposure.
2. The build platform bonds to the first layers and drags the part out of the pool of resin.
3. Laser (in Form printers) or UV light source cures resin.
4. (Special for Form printers) Mirrors attached to galvanometers controls the position of laser point, tracing the contour of a sliced layer.

For MSLA or Masked SLA printers, a LCD screen in front of a powerful UV light source is used to control the exposure region.