Another laser-based additive manufacturing technology is selective laser sintering (SLS). This technology, however, creates a model from dry media instead of liquid.
With SLS, the media, generally plastic or nylon, is placed inside a forming chamber, again containing a movable surface. The media is a particle with a texture somewhere between granulated sugar and flour. The chamber temperature is then raised to just below the melting point for the selected media.
A mirror-directed laser beam draws a profile of the desired model into the warm media. The energy pushes the media’s surface temperature just above its melting point, causing the particles to fuse together or sinter.
The surface then drops a fraction of a millimeter and a wiper sweeps a fresh, level layer of media across the work field. The process repeats again and again, creating a model in much the same manner as most 3D printing processes.
Variations of SLS include direct metal laser sintering (DMLS) or selective laser melting (SLM), which apply a similar technique to metals.
Pros and Cons
A distinct advantage of SLS printing over FDM and SLA is that it can produce parts with much higher strengths. Additionally, the SLS process requires no supports, as the level of the unsintered media rises with that of the sintered product, acting as support material for the model being manufactured. This means complex structures are generally much easier to produce with SLS.
Once sintering is complete, most SLS models require only a gentle post-process media blast, similar to sandblasting, to sweep away any remaining unsintered particles.
SLS is not without its downsides. The main drawback is accessibility. Because the technology requires a high power laser, SLS machines are both expensive and unsafe to operate in anything less than a workshop type of space.
Furthermore, as the process involves particles that are only surface liquefied, finished projects tend to exhibit rough, grainy surfaces. This can be mitigated through the post-print blast cleaning process, but SLS alone will never produce a smooth, shiny surface.
That being said, the technology is a popular choice for rapid industrial manufacturing. As CO2 laser packages continue to drop in price, it is only a matter of time before SLS printing becomes a popular hobby option.