Stereolithography is widely known as the first 3D printing process to be commercialized. Stereolithography is a laser-based process that works with photopolymer resins that react with a laser to form a precise object later. The laser beam is directed at X-Y angles across the surface of the resin according to 3D data delivered to a computer (.stl file) where the resin is fixed precisely where the laser strikes the surface. When the layer is complete, it returns to the Z position and then repeats the process until the object is completed.
Due to the nature of this process, printing support is required for some parts, especially those with hanging parts. These parts are removed manually after printing. Objects made by this process must be cleaned and treated by chemical processes. Stereolithography is generally accepted as one of the most precise 3D printing processes. However, limiting factors include post-press processing and material stability over time, which can become brittle.
DLP (Digital Light Processing)
This process is similar to stereolithography because it works with photopolymers. The main difference is that light is the source. DLP uses a conventional light source, such as an arc lamp, with a liquid crystal display or a curved mirror, which is applied to the entire surface. DLP produces high-precision parts with excellent resolution, but also requires material support as in stereolithography. However, one of the advantages of DLP over SL is that a small amount of resin is required to carry out the process, which generally results in less waste and lower production costs.
Laser sintering / Laser melting
Laser sintering is a term that refers to a laser-based 3D printing process that works with powder material. The laser is traced over a substrate with powdered material based on 3D data obtained by a computer, in the X and Y axes. When the laser interacts with the surface of the powder material, it sinters the particles and creates a solid shape. After finishing each layer, the powder substrate falls off, and the roller processes the powder and so on until the whole printing process is completed. The printing chamber is completely closed so that it can maintain a precise temperature during the melting of the powder material. However, due to the high temperature required for laser sintering, the cooling time is longer. Porosity is also a problem with this process, so some applications require mixing with other material to improve mechanical properties.
Laser sintering can process plastic and metal materials. The parts produced in this way are more durable than the pieces produced in the SL or DLP process, although the end surface of the object and the precision are not high.
Extrusion / FDM
Plastic extrusion 3D printing is the most common 3D printing process. The most famous name is FDM or fusion deposition modeling. The process takes place by melting plastic deposited using a heated extruder, layer by layer on a platform based on 3D data obtained from a .stl file.
Stratasus has developed a wide range of industrial materials for the FDM process that is suitable for manufacturing applications. The most commonly used materials for this process are ABS and PLA. The FDM process requires support in the material during printing due to objects that have hanging parts. These auxiliary parts are easily separated after the printing of the object is finished because water-soluble materials are used. Alternatively, when plastic is used during printing as a support, then the part must be separated by hand by breaking, filing, and subsequent processing of the model to achieve a better appearance of the surface.