SLS vs. SLM: Differences and Comparisons
Learn about the differences between these two 3D printing technologies.
Selective laser sintering (SLS) is an additive manufacturing (AM) process in which a laser methodically sinters the particles of a polymer-based powder and builds parts layer by layer. It is one of our most popular 3D printing processes at Xometry; to learn more, visit our SLS 3D printing service page.
Selective laser melting (SLM) is another form of AM but utilizes a metal powder (pure or alloy) instead. Despite these similarities, the three main differences between SLS vs. SLM are the material used to build the parts, the process used to build them, and the cost.
Since a metal powder is melted in SLM, the build process between the two machines is different. An inert gas (argon or nitrogen) must be pumped into the build chamber to facilitate melting. Consequently, high temperatures present within SLM systems necessitate sufficient cooling for parts before they are removed.
For both SLS and SLM, build times can be long. Also, the complexity of their technologies makes both processes relatively expensive. Regardless, one main advantage of SLS is that it can produce parts reflective of a plastic-injected part faster. SLM’s main advantage is that it can produce metal parts that otherwise would be non-machineable. Both systems can be excellent ways to expedite time-to-market via rapid prototyping and low-to-medium volume production.
In this article, we dive deeper into the differences and similarities of SLS vs. SLM to help provide a better understanding of which system is best for a project.
SLS Definition and Comparison to SLM
SLS was developed in the mid-1980s at the University of Texas at Austin with funding from the US Department of Defense. Patents for these AM processes have long expired, and many companies have developed lower-cost options for 3D-printer systems since.
SLS builds parts using a CO2 laser that selectively sinters and fuses thermoplastic polymer granules. When a layer is completed, the build platform descends and another layer of powder is deposited for sintering. This process repeats until the part is completed. Completed parts must cool, for up to 12 hours, before they are cleaned with compressed air or other blasting media. Compared to SLM, SLS can be considered an identical process except for thermoplastics rather than metals.
To learn more, see our guide on What is SLS.
Advantages of SLS Compared to SLM
- SLS-printed parts have excellent mechanical properties.
- SLS easily makes parts complex geometries since no supports are needed.
- SLS allows the recycling and reusing of unsintered powders.
Disadvantages of SLS Compared to SLM
- SLS printers have long lead times since only industrial-scale SLS printers are widely available.
- SLS parts commonly have poor and grainy surface finishes and may require post-processing to achieve desired surface finishes.
- Warping and oversintering can occur on large, flat surfaces and small holes in SLS-printed parts.
SLM Definition and Comparison to SLS
SLM was developed at the turn of the 21st century at the Fraunhofer Institute in Germany. The potential impact SLM has on the manufacturing industry is immense. A range of metals can be used in SLM processes and SLM parts have properties equivalent to metal parts fabricated through traditional processes.
Like SLS, SLM builds parts using a high-powered laser and a powdered material. Unlike SLS, SLM systems melt powders to build parts and form compact, homogenous structures. Moreover, entire layers of a part are melted at once. When a layer has solidified, the build platform descends. Another layer of powdered metal is deposited for the process to repeat until the part is completed. The entire printing process occurs within a controlled environment; inert gases like argon or nitrogen are pumped into the system to facilitate melting. Completed parts must cool sufficiently before being removed from the printer.
SLM is similar to SLS in terms of process. The only major difference is the material used: SLS creates plastic parts, and SLM creates metal parts. The image below shows a typical SLM 3D printer:
Advantages of SLM Compared to SLS
- SLM can reduce manufacturing lead times and tooling costs.
Disadvantages of SLM Compared to SLS
The disadvantages of SLM compared to SLS are listed below:
- SLM systems are expensive due to their costly technology and equipment.
- SLM requires extensive post-processing to achieve desired surface finishes.
- SLM requires increased material usage due to the need for support for overhangs on parts during printing.
| Attribute | SLS | SLM |
|---|---|---|
Attribute Uses thermoplastic powder | SLS Yes | SLM No |
Attribute Uses metal powder | SLS No | SLM Yes |
Attribute Inert gas needed | SLS No | SLM Yes |
Attribute Extensive range of materials | SLS No | SLM Yes |
Attribute Use for functional prototypes and small-to-medium-sized production | SLS Yes | SLM Yes |
Attribute Extensive post-processing required | SLS Yes | SLM No |
Attribute Need for supports | SLS No | SLM Yes |
Attribute Complex geometries | SLS Yes | SLM Yes |
Attribute Costly | SLS Yes | SLM Yes |
Table. SLS vs. SLM Comparison
Comparisons of SLS and SLM
Technology comparison: Both SLS and SLM systems have similar complex technologies and processes. They use high-powered lasers, thermoplastic or metal powders, and specialized 3D-printing environments. The primary differences between the two forms of AM as it relates to technology are the addition of gas and the need for a special printing environment for SLM processes.
Material comparison: SLS prints parts from thermoplastic powders such as Nylon 11, Nylon 12, and its derivatives. SLM prints parts from pure metal or alloys. While nylons are predominantly used in SLS, the possible materials that can be used with SLM are much more extensive.
Product applications comparison: Possible product applications of SLS vs. SLM depend on whether a thermoplastic or metal part would be more ideal. While both AM methods can provide parts that are environmentally stable, deciding between the two ultimately comes down to two factors: load bearing and weight. SLM may be the better option if higher loads are exerted on the parts. If light weight is more critical, SLS may be better.
Print volume comparison: The print volumes for SLS and SLM are similar since the two AM methods are nearly identical. SLS printers can have print volumes up to 550 x 550 x 750 mm while SLM printers can have volumes up to 350 x 350 x 350 mm. There isn’t a substantial difference in print volume between the two.
Surface finish comparison: SLS printers produce parts with excellent surface finishes, but sometimes leave surfaces feeling grainy and powdery. Surfaces can be post-processed with blasting media such as water jet or sand, spray painting, or lacquering. SLM printers can produce metal parts with exceptional surface finishes that seldom require post-processing. SLM parts can be post-processed to increase corrosion resistance.
Cost comparison: Because both SLS and SLM systems use complex, advanced technologies, they can be expensive. SLS systems start as low as $18,000 and can go as high as $100,000. SLM printers are more costly. They range from $55,000 to $350,000.
Summary
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