Stereolithography Process, How it Works?

The #stereolithography process, also known as #SLA , uses the photo-#polymerization principle to produce 3D #models using #UV-sensitive #resin. This is not to be confused with STL files, which are 3D printing files. This is #solidified by the passage of a #laser layer after layer. It provides one of the most qualitative printing surfaces of existing 3D printing technologies.
From a historical point of view, Stereolithography is considered the process behind #3D #printing. The first patent application was filed in 1984 by Chuck Hull and marketed by 3D Systems in 1988.
3D SLA printers use liquid printing material and a UV protection cover (usually orange, green, red or yellow). Stereolithography offers a relatively small volume of production compared to other printing technologies.
- How Stereolithography 3D Printing Works
As with any 3D printing technique, a 3D #digital file is required. This can be obtained via CAD #software (SolidWorks, Sculpt or SelfCAD for example). These files, are to a slicer, which cuts the model into thin layers to print. The instructions are then sent to the 3D printer.
Stereolithography #machines contain a resin tray, a #mobile #platform (Z axis), a scraping system (X axis), a UV laser, focusing optics and a mirror galvanometric (X and Y axes).
The laser beam sweeps the surface of the #liquid resin according to the digital 3D model supplied to the #printer. After one layer has been solidified, the platform descends a level. The next section is then solidified. There are as many printing cycles as there are layers necessary to obtain the complete #volume of the piece.
- Post-printing
Once the printing is finished, a step of cleaning the room, using a #solvent (usually isopropyl alcohol also called isopropanol), is necessary in order to remove the excess non-solidified resin. Unlike other techniques such as Selective Laser Sintering (SLS), Fused Deposition Material (FDM), and PolyJet 3D printing, UV post-treatment is usually required to finalize the photo-#polymerization process to maximize the #strength of the #material.
As with fused deposition #technology, SLA uses scaffolds when printing complex shapes. In the manner of a scaffolding, they allow supporting the parts that dash in the vacuum. They are removed during post-processing.
Stereolithography technology offers a slightly #vitreous surface finish but is generally superior to FDM or SLS processes (for the same layer thickness). 
It is not uncommon that the different layers of printing are barely visible. However, few colours are available in SLA.