How stereolithography works?
There are two main types of SLA printers, namely bottom-up and top-down constructions. In bottom-up printers, the build platform goes down to the height of a single layer from the bottom of the vat, and the first layer is cured by the light source through the vat transparent bottom. Then the platform goes up and the next layer is cured. Each time the platform rises, the cured layer has to be detached from the bottom of the vat, and this peeling step restricts the possible build size, as a part too big can deform or detach from the build plate because of the jerks. The bottom-up design is used mainly in desktop devices as it is less expensive in production and easier to operate.
In the top-down construction, the build platform starts from the surface of the polymer in the vat, just lowering under it for one layer height, and then gradually descends while the layers are cured by the light source placed above the vat. Such design allows for larger build volumes and the use of fewer support structures, and it is typical of industrial-grade machines.
Alternative processes: DLP and LCD
Apart from SLA, there are two more types of vat photopolymerization technology which are DLP and LCD resin 3D printing. Both technologies utilize the same process of selective curing liquid polymers with the only difference in the light source used for layer solidification.
DLP (digital light processing) devices employ a light projector, while in LCD (liquid crystal display) machines, also known as masked SLA (MSLA), an LCD matrix serves as a mask to transmit the light from an array of LEDs in the required areas. Both DLP and LCD technologies have the speed advantage over SLA, as they cure the entire layer at once, opposed to point-by-point curing by a laser beam. However, SLA generally boasts smoother surface finish. As all the three technologies are fundamentally similar in workflows and use the same materials, all of them are often referred to as stereolithography, or simply SLA 3D printing.
Credits Sources: https://top3dshop.com/blog/stereolithography-3d-printing-in-detail