Full name of SLS technology is selective laser sintering. It is one of an additive manufacturing (AM) technology that uses a high precision laser to sinter plastic powders like PA11, PA12 and PA6 into a solid structures. Sintering process is based on a 3D model.
SLS has been becoming more and more useful and popular in rapid prototyping and manufacturing processes from decades. Low unit cost of manufacturing the part and high precision and productivity made SLS technology ideal for a range of applications from functional prototyping to shot series manufacturing.
Selective laser sintering was one of the first additive manufacturing techniques. It was developed in the mid-1980s by Dr. Carl Deckard at the University of Texas at Austin. Since then SLS method has been adapted to work with a range of materials, including plastics, metals, glass, ceramics, and various composite material powders. Nowadays the two most commonly used powder bed fusion systems t are plastic-based SLS, and metal-based, known as direct metal laser sintering (DMLS) or selective laser melting (SLM). For many years both have been expensive and complex, so not many could afford to use them in daily rapid prototyping and rapid manufacturing.
Innovation in the field has surged recently, and plastic-based SLS is now poised to follow other 3D printing technologies like stereolithography (SLA) and fused deposition modeling (FDM) to gain widespread adoption with accessible, compact systems.
After patentes have expired the SLS technology has bagan to be more common and avaiable – many new producers started producing SLS devices. At the moment there is over a dozen major manufacturers offering their devices for various segments of users.
How it works
SLS 3D printers use a high power laser to fuse small particles of polymer powder. Different producers use different lasers. It is a myth that the most important here is laser power. Even though the lasers power used in modern SLS is between 40 – 100 W – rarely user uses its full power. What is more important in laser sintering process is stable heating and accuracy of the laser beam dot. Just like all methods of 3D printing, an object printed with an SLS devices starts as a computer-aided design (CAD) file. CAD files are converted to .STL format, which can be understood by a 3D printer.
Objects printed with SLS technology are most commonly made with plastic powder materials, such as nylon( PA11, PA12 and also high temperature PA6), which are dispersed in a thin layer on top of the build platform inside an SLS machine.
A laser, which is digitally controlled tells it what object/ shape to sinter. It pulses down on the platform, tracing a cross-section of the object onto the powder. The laser heats the powder either to just below its boiling point (sintering) or above its boiling point (melting), which fuses the particles in the powder together into a solid form. After one by another layer is formed, the platform of the SLS machine goes down — usually by less than 0.1mm — so a new layer of powder is exposing and ready to sinter and fuse together. The actions is repeating again and again until the object has been ready.
When the object is finally formed, it is usually left to cool in the machine before being removed. But in Sonda SYS SL02 device it is required to left it just too cool down. The object can be removed after 1-2 hours (depending on shape and size) and the other building chamber size can be used almost immediately.
Unlike other methods of 3D printing, SLS requires very little extra tooling, meaning that objects don’t usually have to be sanded or altered once they come out of the SLS machine. SLS technology does not require the use supports to hold an object together while it is being printed. (as when using another 3DP methods, ex. SLA or FDM). So that is making SLS method much less time-consuming than SLA or FDM.
When printing process is complete and objects removed from building chamber, they have to be separated and cleaned of excess powder. This process is usually completed manually at a cleaning station with use of compressed air or a media blaster.
Very important in selective laser sintering method is high level of precision and tight control during printing process. The temperature of the powder must be controlled within 2 °C during the three stages of preheating, sintering, and storing before removal full build parts. It is the term of that allows to minimize warping, stresses, and heat-induced distortion.
SLS parts have a slightly rough, grainy surface finish right out of the printer similar to a medium grit sandpaper. Nylon provides a range possibilities for post-processing, such as tumbling, dyeing, painting, stove enameling, metal coating, bonding, powder coating, and flocking.
Minimal material losses
After printing process completed and part recovery from building chamber the powder is filtered to remove larger particles and can be recycled. Even though unfused powder degrades slightly with exposure to high temperatures, it can be used after being refreshed with new material for subsequent print jobs. This ability to re-use material makes SLS one of the least wasteful manufacturing methods.