Selective laser sintering
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Selective laser sintering (SLS) is an additive manufacturing technique used for the low volume production of prototype models and functional components. Selective Laser Sintering uses lasers as its power source to sinter powdered material, binding it together to create a solid structure. It is often confused with another similar process called Selective Laser Melting (SLM), the difference being that it only sinters the powders together as opposed to achieving a full melt. 
Selective Laser Sintering (SLS) was developed and patented by Dr. Carl Deckard and academic adviser, Dr. Joe Beaman at the University of Texas at Austin in the mid-1980s, under sponsorship of DARPA. Deckard and Beaman were involved in the resulting start up company DTM, established to design and build the Selective Laser Sintering Machines. In 2001, 3D Systems the biggest competitor of DTM and SLS technology acquired DTM. The most recent patent regarding Deckard's SLS technology was issued 28 January 1997 and expired 28 Jan 2014.
A similar process was patented without being commercialized by R. F. Housholder in 1979.
An additive manufacturing layer technology, SLS involves the use of a high power laser (for example, a carbon dioxide laser) to fuse small particles of plastic, metal (direct metal laser sintering), ceramic, or glass powders into a mass that has a desired three-dimensional shape. The laser selectively fuses powdered material by scanning cross-sections generated from a 3-D digital description of the part (for example from a CAD file or scan data) 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.
Because finished part density depends on peak laser power, rather than laser duration, a SLS machine typically uses a pulsed laser. The SLS machine preheats the bulk powder material in the powder bed somewhat below its melting point, to make it easier for the laser to raise the temperature of the selected regions the rest of the way to the melting point.
Unlike some other additive manufacturing processes, such as stereolithography (SLA) and fused deposition modeling (FDM), SLS does not require support structures due to the fact that the part being constructed is surrounded by unsintered powder at all times, this allows for the construction of previously impossible geometries.
Materials and applications
Some SLS machines use single-component powder, such as direct metal laser sintering, powders are commonly produced by ball milling. However, most SLS machines use two-component powders, typically either coated powder or a powder mixture. In single-component powders, the laser melts only the outer surface of the particles (surface melting), fusing the solid non-melted cores to each other and to the previous layer.
Compared with other methods of additive manufacturing, SLS can produce parts from a relatively wide range of commercially available powder materials. These include polymers such as nylon (neat, glass-filled, or with other fillers) or polystyrene, metals including steel, titanium, alloy mixtures, and composites and green sand. The physical process can be full melting, partial melting, or liquid-phase sintering. 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 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.
- 3D printing
- Desktop manufacturing
- Digital fabricator
- Direct digital manufacturing
- Fab lab
- Instant manufacturing, also known as "direct manufacturing" or "on-demand manufacturing"
- Rapid manufacturing
- Rapid prototyping
- RepRap Project
- Solid freeform fabrication
- Von Neumann universal constructor
- "How Selective Laser Sintering Works". THRE3D.com. Retrieved 7 February 2014.
- Deckard, C., "Method and apparatus for producing parts by selective sintering", U.S. Patent 4,863,538, filed October 17, 1986, published September 5, 1989.
- Lou, Alex and Grosvenor, Carol "Selective Laser Sintering, Birth of an Industry", The University of Texas, December 07, 2012. Retrieved on March 22, 2013.
- Housholder, R., "Molding Process", U.S. Patent 4,247,508, filed December 3, 1979, published January 27, 1981.
- Prasad K. D. V. Yarlagadda; S. Narayanan (February 2005). GCMM 2004: 1st International Conference on Manufacturing and Management. Alpha Science Int'l. pp. 73–. ISBN 978-81-7319-677-5. Retrieved 18 June 2011.
- Watch and Learn about Selective Laser Sintering 3D printing
- DMLS – DEVELOPMENT HISTORY AND STATE OF THE ART
- SLS prototype technology overview, advantages, and materials – ProtoCAM
- Step by Step overview of SLS models are built - LPE
- Selective Laser Sintering, Birth of an Industry