Selective laser sintering is a method of manufacturing that uses a high-heat laser to melt powder into a predetermined shape. This process is a type of additive manufacturing, meaning the item is built up from materials into a final form. This is in contrast to the more common subtractive manufacturing where material is removed from a piece until it reaches its final shape. Selective laser sintering requires a computer model or description of the final piece. The laser guidance program will read the model and slowly build the shape from the available materials.
The selective laser sintering process begins with the creation of a computer representation of the final piece. This representation is often made using design software so the final piece is easily viewed in a virtual space. If design software isn’t used, it is possible to create mathematical or programed models that exist only as code. These pieces can have extremely tight specifications, but are much more difficult to create.
After the model is created, the selective laser sintering program reads the data and activates the laser. This machine is generally a high-temperature industrial laser, such as a carbon dioxide laser. The heat from the laser fuses together powdered material by hitting it with very hot pulses. The action of the laser stops secondary heating, which prevents unwanted materials from sticking to the work piece or creating unintended melting.
The powder used by selective laser sintering is generally a two-part mixture. The inner kernel of the powder is a dense material that provides weight and structure to the final piece. This inner bit is covered in a material that is easily melted, such as nylon or plastic. When a single part powder is used, it is typically made up of sand or metal — two materials that melt well, but still provide structure. Single-part mixtures often result in a higher-quality finished products, but they generally cost more to produce and require a higher heat to melt.
The laser makes the work piece one layer at a time. The powder is melted into a portion of the final piece and allowed to cool. Then the laser makes the next part and then the next, each with a small cooling time in between. Depending on the materials used, the cooling period may be anywhere from a few seconds down to a nearly imperceptible amount of time. As the piece builds up, it requires no outside support, as the excess powder in the tank supports it on all sides.