| SLS (SELECTIVE LASER SINTERING) |
  SLS(Selective Laser Sintering) prototyping methods are usually used to make complex structure parts for loading test. SLS(Selective Laser Sintering) was developed and patented by Dr. Carl Deckard at the University of Texas at Austin in 1989. SLS is an additive manufacturing technique that uses a high power laser to fuse small particles of plastic, metal, ceramic, or glass powders into a mass representing a desired 3-dimensional object. The laser selectively fuses powdered material by scanning cross-sections generated from a 3-D digital description of the part on the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed. Compared to other methods of additive manufacturing, SLS can produce parts from a relatively wide range of commercially available powder materials, including polymers (nylon, also glass-filled or with other fillers, and polystyrene), metals (steel, titanium, alloy mixtures, and composites) and green sand. The physical process can be full melting, partial melting, or liquid-phase sintering. And, depending on the material, up to 100% density can be achieved with material properties comparable to those from conventional manufacturing methods. In many cases large numbers of parts can be packed within the powder bed, allowing very high productivity. SLS is performed by machines called SLS systems. SLS technology is in wide use around the world due to its ability to easily make very complex geometries directly from digital CAD data. While it began as a way to build prototype parts early in the design cycle, it is increasingly being used in limited-run manufacturing to produce end-use parts. One less expected and rapidly growing application of SLS is its use in art. Unlike some other additive manufacturing processes, such as SLA(Stereolithography) and FDM(Fused Deposition Modeling), SLS does not require support structures due to the fact that the part being constructed is surrounded by unsintered powder at all times. Highlights of Selective Laser Sintering * Patented in 1989. * Considerably stronger than SLA; sometimes structurally functional parts are possible. * Laser beam selectively fuses powder materials: nylon, elastomer, and soon metal; * Advantage over SLA: Variety of materials and ability to approximate common engineering plastic materials. * No milling step so accuracy in z can suffer. * Process is simple: There are no milling or masking steps required. * Living hinges are possible with the thermoplastic-like materials. * Powdery, porous surface unless sealant is used. Sealant also strengthens part. * Uncured material is easily removed after a build by brushing or blowing it off. Introduction of Selective Laser Sintering Chief advantages of SLS(Selective Laser Sintering) over SLA (Stereo Lithography Apparatus) revolve around material properties. Many varying materials are possible and these materials can approximate the properties of thermoplastics such as polycarbonate, nylon, or glass-filled nylon. As the figure below shows, an SLS machine consists of two powder magazines on either side of the work area. The leveling roller moves powder over from one magazine, crossing over the work area to the other magazine. The laser then traces out the layer. The work platform moves down by the thickness of one layer and the roller then moves in the opposite direction. The process repeats until the part is complete.  |
