SLA – Stereolithography (and DLP, CDLP, CLIP)
Stereolithography – the very first 3D printing technology was invented in 1983 by Charles Hull, founder of 3D Systems. The first machine was named SLA-1.
How does it work?
The printer consists of a resin bath, moving build platform, and a curing device. The resin is a UV reactive photopolymer.
For SLA, the curing device is a laser beam, whereas it is a light beamed from a projector for DLP, CDLP or CLIP. The curing device can be located either above or below the resin bath. This configuration determines whether the platform moves up or down during the printing.
Classic SLA
Classic SLA 3D printers have the laser located above the resin bath. When starting a print, the build platform is submerged slightly underneath the resin level and moves down incrementally during the printing process. The size of the increment (usually between 0.01 – 0.1mm) determines the thickness of each layer. The first layer of the printed object is solidified using the laser beam and it sticks to the build platform. A roller moves across the build chamber to smooth out the solidified layer. The platform lowers and the whole process repeats iteratively, creating a solid object as a result.
SLA reversed printing direction
Some SLA 3D printers use a translucent resin bath with a laser located below it. When starting a print, the build platform is submerged at the bottom of the bath and moves up incrementally during the printing process. The size of the increment determines the thickness of each layer. The first layer of the printed object is solidified using the laser beam and it sticks to the build platform. The platform moves up and the whole process repeats iteratively, creating a solid object as a result.
Majority of DLP printers
The majority of DLP, CDLP, and CLIP 3D printers have the curing device located underneath a translucent resin bath. When starting a print, the build platform is submerged at the bottom of the bath and moves up incrementally during the printing process. The size of the increment determines the thickness of each layer. The first layer of the printed object is solidified using the light from the projector, which causes it to stick to the build platform. The platform rises and the whole process repeats iteratively, creating a solid object as a result.
In the case of CDLP or CLIP, the printing process works by projecting a continuous film to achieve the curing, as opposed to the slice by slice method.
DLP – Digital Light Projection
CDLP – Continuous Digital Light Projection
CLIP – Continuous Liquid Interface Production
Support structures
The supports are printed from the same material as the rest of the model. This means they have to be later removed manually (with small pliers or by hand). The support structures are usually quite thin, leaving only subtle marks on the printed model that can be removed by brushing and polishing. Some really complex models can be challenging when it comes to support removal.
Applications:
Prototyping of plastic parts
3D printing of transparent objects
Bio-compatible 3D printing (mouth guards, hearing aid products, dental parts)
3D printing of “burnable” models for metal investment casting
3D printing of transparent objects
Manufacturers: 3D Systems, EnvisionTEC, Formlabs, B9Creations, Carbon3D …
