Stereolithography is a manufacturing method where parts are built layer-by-layer using a laser and liquid resin. This is an additive manufacturing process, meaning the part is built up from nothing, as opposed to the more common subtractive process, where material is removed from a work piece to create a finished part. A stereolithography apparatus (SLA) performs the process, but the designs used are typically made using specialized computer-aided design program. These machines are one of the common ways of performing rapid prototyping.
A SLA is actually a very simple machine. The bulk of the machine is the vat where the resin is poured and the part is produced. The bottom of this vat contains a platform that will move up and down in order to facilitate the part’s creation. Above the vat, a free-moving, typically ultraviolet, laser points down into the work area.
When the vat is filled, the platform sits one thickness under the surface of the resin. A thickness varies, but it is the depth that the laser will penetrate into the vat, usually a very small space. When the laser shoots down into the resin, it instantly cures a small amount of material. The platform then descends one thickness and the laser fires again. The platform continues to descend until the entire part is created.
The material in the vat is typically a photopolymer resin. These synthetic materials have special properties when exposed to some form of heat or light. The types of resins used in stereolithography turn directly from a liquid to a solid when exposed to certain wavelengths. This prevents most stereolithography-produced parts from needing a curing phase.
One of the more common uses of stereolithography is in rapid prototyping. When a company is testing a product, it is generally very cost-inefficient to retool existing manufacturing machines to create the prototype. Most teams will use some form of rapid prototyping, where unusual parts are made specifically for the test product. Many of these rapid processes use additive techniques, since one machine can make a huge variety of different parts.
The resins used in the creation process are non-supportive. This means that if a part is unstable, supports will need to be created along with the piece in order to hold its weight. When the part is finished in the SLA, it will need to have the supports removed by hand. Other types of rapid prototyping processes are supportive, meaning no additional supports are made during creation.