SLA (Stereolithography Apparatus) – Process using photosensitive resins cured by a laser that traces the parts cross sectional geometry layer by layer. SLA produces accurate models with a variety of material choices.
The SLA rapid prototyping process was the first entry into the rapid prototyping field during the 1980’s and continues to be the most widely used technology. The SLA method uses liquid photopolymer resins that are solidified by a laser to generate parts. An SLA machine consists of the following parts: a build platform, resin vat, recoating blade, ultraviolet laser and a scanning device. The build platform, which translates up and down, is suspended in the vat of resin. The build platform is placed slightly under the surface of the resin. A laser beam hardens the resin when it makes surface contact. A scanning device, which controls the laser beam, traces the first cross section of the prototype. The laser will trace the part as well as support structures necessary to support any overhanging features. Once the first cross section is complete, the build platform lowers one layer thickness into the vat. A recoating blade is then used to hasten the process of covering the cross section with liquid resin. Once the first cross section is suitably covered, the next cross section is scanned. This process repeats until the part is complete. Once the part is completed, the build platform is raised and the excess resin is allowed to drain. Depending on the material, a post cure operation is sometimes needed to attain the desired material properties. After any final curing, the support structures that were built to prevent any sagging are removed.