Selective Laser Sintering (SLS)
Selective Laser Sintering (SLS) is a powerful additive manufacturing technology. It can be used to produce complex, durable, strong and fully functional parts. It is one of the most popular technologies for both, rapid prototyping and small batch series production (‘rapid manufacturing’). The most common material is PA12 (‘Polyamide 12’), called PA2200 when in powder form or commonly known as ‘Nylon’. The material is durable, flexible when thin and strong when printed in thicker structures.
Unlike most other 3D printing technologies, Laser Sintering does not require any support structures so imposes few limitations on your design. As a result, it has become the method of choice for 3D printing complex geometries. Those characteristics have made SLS an established production method for functional prototypes and small batch production of a wide range of plastic products.
A plastic powder (typically PA12, with a grain size of around 60 microns) is spread evenly on a build platform. The material is compacted by a scraper or drum and heated up. On this dense layer, a laser draws the first layer of the object. During this process, the laser sinters the powder (heats to near its melting point), allowing it to fuse with adjacent powder granules. This process continues repeatedly until the whole object is completed. During printing, the object is stabilized by the un-sintered compacted powder around it, eliminating the need for a support structure.
After printing is completed, the parts must cool-down slowly, which takes in total around 10 hours or more. After cooling, the objects are extracted from the printer, excess powder is removed, and the parts are cleaned by glass bead blasting.
Because of the slow print cycle and long cool-down, the printing times are long – taking up to 2 or even 3 days even before conducting post-production finishing.
Illustration of the printing process by 3D Systems
Laser sintering is used for both, rapid prototyping and rapid manufacturing of end-use parts. PA12 is a commonly used plastic in a wide range of applications across all major industries, e.g. aerospace, automotive industry, electrical appliances or medical technology. There are plenty of advantages of PA12, which have made the probably most popular polymer in industrial 3D printing: mechanic strength, heat resistance, biocompatibility and durability. Furthermore, the sintering process creates light parts with densities of just approx. 0.95 g/cm³, which makes it a great technology for light weight applications.
Due to the high mechanic strength and heat resistance, PA 12 is the most common material for functional prototypes. Besides these characteristics, it imposes virtually no limits on the geometry, since support structures are not needed. In rapid prototyping, laser sintering is typically used to produce cases, mechanical parts, fixtures or structural components.
The mechanical and thermic properties of PA12 make it a commonly used material for end-use plastic parts. Typical applications are the small production of plastic parts below injection molding quantities (typically 300 – 1.000 parts).
While laser sintering does not offer similar surface quality with resin technologies, like stereolithography or polyjet / mutlijet modeling, it has the advantage of stability and creating extremely complex shapes. Another advantage is that the material PA12 can be dyed quite easily, so that different parts can be ordered in different colors. It is therefore a commonly used technology to create resistant and complex visual models.
- No support structures required – very complex parts can be printed
- Material characteristics perfect for functional and end-use parts
- Interlocking and moving parts can be printed in one piece
The most commonly used material for laser sintering is PA12 (PA2200). However, there are lots of other polymers used, e.g. PA11, PA6 or PA12 compounds (carbon reinforced, aluminum-PA12 mix called Alumide, etc.). Other popular material types are elastomers, such as TPU or TPA. Other available materials include special purpose plastics like PEEK or even metal powders.
PA12 / PA2200 (‚Nylon‘)
PA12/PA2200 is the most used material for laser sintering. The material color is white, but it can be dyed into all major colors. It’s mechanic and thermic properties are perfect for mechanic, structural and all kind of plastic end-use parts.
Alumide is a compound of PA12 and aluminum powder. Compared to pure PA12, it is more rigid and has improved thermic properties. However, the material has a lower abrasion resistance and should not be used for dynamic or moving parts.
Laser sintered PA12 and Alumide parts can be well processed after printing. Our post-process options include:
- Polishing (tumbling, creates nice, smooth surfaces but could impact some small details and round some edges)
- Dyeing (Black, Blue, Red, Yellow, other colors on request)
- Impregnation (water-proofing)
- Spray painting (individual colors)
- Shot peening (creating a dense, semi-glossy and scratch resistant surface)
Selective Laser Sintering was invented and patented by Dr. Carl Deckard and his Professor Dr. Joe Beaman of the University of Texas at Austin. In a project for Defense Advanced Research Projects Agency (DARPA).
During the project, the research team filed their first patents in the mid 1980’s (‘Method and apparatus for producing parts by selective sintering‘). Based on this technology, Deckard and Beaman founded a spin-off company called Desk Top Manufacturing Corporation (DTM Corp.).
DTM became a part of 3D Systems in 2001 and the majority of DTM’s patents for SLS expired in early 2014. This opened the market to a broader range of manufacturers. Today, there is a larger number of companies producing SLS machines, among them the current market leader in the technology EOS.
Interestingly, in 1979 the researcher Ross F. Housholder developed a very similar technology, which he decided not to commercialize. It took another 10 years before the technology actually hit the market.
Drawing of one of the latest patents from 1997, (c) GooglePatents
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