Unlike the desktop printer you use to print documents, SLA machines don’t extrude ink or some other liquid onto a surface. Instead an SLA machine starts with an excess of liquid plastic, some of which is cured, or hardened, to form a solid object. SLAs have four main parts: a tank that can be filled with liquid plastic (photopolymer), a perforated platform that is lowered into the tank, an ultraviolet (UV) laser and a computer controlling the platform and the laser. In the initial step of the SLA process, a thin layer of photopolymer (usually between 0.05-0.15 mm) is exposed above the perforated platform. The UV laser hits the perforated platform, “painting” the pattern of the object being printed.The UV-curable liquid hardens instantly when the UV laser touches it, forming the first layer of the 3D-printed object. Once the initial layer of the object has hardened, the platform is lowered, exposing a new surface layer of liquid polymer. The laser again traces a cross section of the object being printed, which instantly bonds to the hardened section beneath it. This process is repeated again and again until the entire object has been formed and is fully submerged in the tank. The platform is then raised to expose a three-dimensional object. After it is rinsed with a liquid solvent to free it of excess resin, the object is baked in an ultraviolet oven to further cure the plastic. Objects made using stereolithography generally have smooth surfaces, but the quality of an object depends on the quality of the SLA machine used to print it.
The amount of time it takes to create an object with stereolithography also depends on the size of the machine used to print it. Small objects are usually produced with smaller machines and typically take between six to twelve hours to print. Larger objects, which can be several meters in three dimensions, take days.
