Nowadays, 3D printers have been developed for many years. There are more and more 3D printer technologies, materials, processes, etc. It is difficult for ordinary users to recognize meaning of some abbreviations, such as: SLS, SLA, FDM, FFF, ABS, PA, PLA.. .... And we often encounter users' comparisons of 3D printer technology. People often ask: "What is difference between SLA technology and SLS technology?" So in this article we would like to share with you similarities and differences between these two 3D printing materials and technologies to help you find out which technologies are suitable for different 3D printing projects.

Acronym of SLS (Selective Laser Sintering) is defined in Chinese as "selective laser sintering", which is core of this 3D printer technology. Selective laser sintering process is to use a powder spreader to spread a layer of powder material on upper surface of formed part, heat it to a temperature just below sintering point of powder. Control system controls laser beam to scan on powder according to cross-sectional profile of layer, so that temperature of powder is raised to melting point, sintered, and bonded with molded part below. When sintering of cross-section of a layer is completed, worktable is lowered by thickness of one layer, spreading roller spreads a layer of uniform and dense powder on it, sinters cross-section of new layer until the entire model is completed. During molding process, unsintered powder supports cavity and cantilever part of model, there is no need to create a support process structure like SLA process.

 

Chinese definition of SLA (Stereo Lithography Apparatus) is stereo light curing molding technology. It is the first additive manufacturing technology to be theorized and patented in the 1980s. Forming principle is mainly that near-ultraviolet laser beam is focused on a thin layer of liquid photopolymer resin, and plane part of required model is drawn quickly. Thanks to physical characteristics of UV light source, photosensitive resin undergoes a curing reaction under irradiation of UV light, thereby forming a single plane layer of model. Process of applying a new layer of resin on the top and iterating each part of model will finally get a complete 3D printed model. Final step is to clean final model soaked in liquid resin, and usually do not remove support structure.

 

Unlike SLS 3D printers, which are mainly used in industrial production and have strict requirements on environment, SLA 3D printers can be manufactured in an ordinary office environment, which is more friendly to people.

Although current market does not provide standardized resolution parameter range requirements for these two technologies of 3D printers, however, due to different production decisions of each 3D printing manufacturer, we can see that there will be 3D printers with different resolutions on the market. 3D printers of these two technologies use electric platforms. In addition, these two technologies also use focused laser beams to cure 3D printing materials, but because they use completely different wavelengths (SLA is ultraviolet and SLS is infrared), their focus sizes are also quite different. Focus point of ultraviolet lasers is significantly smaller than that of infrared lasers, so SLA 3D printers can usually achieve higher resolution in horizontal and vertical directions!

SLS 3D printers can use a variety of powder materials, the most common is polyamide (usually nylon PA12), they can use different additives to change color, strength, flexibility, stiffness and other properties. You may not know this material, but you must have heard of "nylon" substrate, which has better durability, strength and extraordinary wear resistance.
For SLA 3D printers, usually 3D printing manufacturers recommend using their own photosensitive resin materials, but there are still many third-party manufacturers' materials to choose from, which are usually cheaper than original factory. Generally speaking, many extension materials based on nylon materials are generally developed on the market. They are often harder than nylon substrates but are therefore brittle, have softer and more flexible characteristics, and are very similar to rubber materials.

Surface finish is the first comparison dimension for all users after getting finished product. With SLS printers, a porous solid material is essentially produced during sintering process, because air in powder initially creates tiny bubbles on sintered material. Although this is something you can't see with naked eye, it feels a bit "rough" when you touch it. Solid surface smoother finished product can be printed by polymerization of liquid photosensitive resin after curing.

 

Surface quality of model printed by SLA 3D printer is very good
General nylon powder provides basic options: black and white, used for 3D printing materials for users to choose. By mixing these two colors of materials, gray nylon materials can also be provided to users, but it can be said that choice of this color is still quite limited, and there is no choice of translucent or transparent SLS technology 3D printing materials. Photosensitive resin materials used in SLA 3D printers have more color choices.

For 3D printed models without obvious fixed positions (such as balls), or some models with suspended parts (such as lampshades of desk lamps), almost all 3D printing technologies require supporting materials or structures. SLS 3D printers are an exception, thanks to unsintered powder around model during printing process using SLS technology, which can be used as a support material to achieve support-free printing during printing process.
In 3D printing model structure of some complex structures printed by SLA technology, users usually need to sacrifice a certain model quality so that printed model can add as little support material as possible. Therefore, it is necessary to weigh pros and cons when using SLA 3D printer to print model. When using support structure, printed cost requires post-processing work, but even so, it will still leave a mark where support is removed, which will affect surface finish.

Both technologies have their own advantages and disadvantages, but final choice still depends on user's needs for model. For models that focus on functional use, SLS technology may be the best choice. And if pursuit is to show these conventional applications in models, material strength will not be pursued too much, and SLA technology can better reflect its advantages.
Finally, editor made a parameter comparison table of the two technologies for your reference.