Principle and Working of Stereo Lithography Apparatus (SLA)

SLA is based on photopolymerization, in which liquid photosensitive resin is converted into a solid polymer when exposed to suitable light.

Working

1. A CAD model is converted into layers by slicing software.
2. The build platform is positioned in a vat containing photopolymer resin.
3. A UV laser or projected UV light selectively exposes the resin according to the first layer.
4. Photoinitiators in the resin absorb light and initiate polymerization, causing the exposed resin to solidify.
5. The platform moves by one layer thickness.
6. Fresh liquid resin flows or recoats the build area.
7. The next layer is exposed and bonded to the previous layer.
8. The cycle continues until the complete component is built.
9. The part is removed, washed to remove uncured resin and usually post-cured to achieve the required properties.

Role of photopolymerization

Light initiates chemical reactions that link monomer molecules into polymer chains. The exposure dose, wavelength, resin formulation and curing conditions affect cure depth, dimensional accuracy, surface quality and final mechanical properties.

Conclusion: SLA provides high resolution and fine surface detail because the part is formed by controlled optical curing of liquid resin.