SLS vs. FDM: Differences and Comparisons
Learn about the differences between these two 3D printing technologies.
Selective laser sintering (SLS) and fused deposition modeling (FDM) are two types of additive manufacturing (AM), otherwise known as 3D printing. Both are regularly employed for rapid prototyping and low-to-medium-volume production. SLS machines methodically fire a laser to sinter the particles of a polymer-based powder to build parts layer-by-layer. FDM machines, on the other hand, melt and extrude a polymer filament through a nozzle, depositing it along a prescribed path to form parts layer-by-layer. While the two types of AM have many similarities, their differences will determine whether SLS vs. FDM is better for you.
The three main differences between the two include: they operate via different processes, they require different types of post-processing, and one is significantly more expensive than the other. Because SLS machines selectively fuse small particles, dedicated support structures aren’t needed. This enables the creation of complex geometries, interior features, and undercuts. It also makes post-processing simpler. SLS parts have excellent mechanical properties similar to those of plastic-injected parts. However, all this precision makes SLS more expensive. FDM is more cost-effective than SLS. It is still capable of producing parts at similar speeds, but with lower resolutions.
In this article, we will dive deeper into the differences and similarities of SLS vs. FDM.
SLS Definition and Comparison to FDM
SLS was developed in the mid-1980s at the University of Texas at Austin with funding from the US Department of Defense. Since the patents have long expired, many companies have developed lower-cost 3D-printer systems themselves that use the same basic technology.
Most SLS systems create parts via a CO2 laser that selectively sinters and fuses thermoplastic polymer granules. Once one 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 (sometimes up to 12 hours) before they are cleaned with compressed air or other blasting media. While more expensive than FDM, SLS can create parts at greater resolution with excellent mechanical properties and complex geometries. The image below is an example of an SLS 3D printer:
SLS 3D printer.
Image Credit: Shutterstock.com/Moreno Soppelsa
What Are the Advantages of SLS Compared to FDM?
Listed below are the advantages of SLS vs. FDM:
- Excellent mechanical properties make SLS parts great for both end-users and as prototypes.
- Complex geometries are simple with SLS since no supports are needed.
- SLS quickly completes small-to-medium-sized batch production.
- SLS allows the recycling and reuse of unsintered powder.
What Are the Disadvantages of SLS Compared to FDM?
Listed below are the disadvantages of SLS vs. FDM:
- Long lead times for SLS printers since only industrial-scale SLS printers are widely available.
- SLS often produces grainy surface finishes which may require post-processing.
- Warping and oversintering can occur on large flat surfaces and small holes of SLS-printed parts.
FDM Definition and Comparison to SLS
FDM was developed in the late 1980s. Once patents expired for the proprietary 3D-printing process in 2009, commercial and industrial entities began developing their own FDM systems. Today, FDM is the most common form of 3D printing.
Like SLS, FDM utilizes thermoplastics to produce parts. However, FDM produces parts via the extrusion of a thermoplastic filament. Plastic is fed through a heated nozzle where it is melted and then deposited onto the build tray. Once the preceding layer has cooled, the next layer is deposited. This continues layer-by-layer until the part is completed. FDM is a much more cost-effective form of AM than SLS and can be a good entry point for smaller manufacturers. The image below is an example of an FDM 3D printer:
FDM 3D printer.
Image Credit: Shutterstock.com/Moreno Soppelsa
What Are the Advantages of FDM Compared to SLS?
Listed below are the advantages of FDM vs. SLS:
- Lower costs make FDM a great point of entry for smaller manufacturers.
- Simple and user-friendly technologies and displays make FDM easy to use.
- Some FDM machines are very large, making large parts possible.
What Are the Disadvantages of FDM Compared to SLS?
Listed below are the disadvantages of FDM vs. SLS:
- The lower resolution makes FDM less desirable for small and/or detailed parts.
- Slower print times mean FDM isn’t ideal for large production runs.
- Many FDM parts tend to warp and shrink.
| Attribute | SLS | FDM |
|---|---|---|
Attribute Easy to use technology | SLS Yes | FDM No |
Attribute Easy to use technology | SLS No | FDM Yes |
Attribute Use for proof-of-concept prototypes | SLS Yes | FDM Yes |
Attribute Large print volume | SLS No | FDM Yes |
Attribute Use for functional prototypes and parts | SLS Yes | FDM No |
Attribute Need for supports | SLS No | FDM Yes |
Attribute Complex geometries | SLS Yes | FDM No |
Attribute Costly | SLS Yes | FDM No |
Table. SLS vs FDM Comparison
If your project requires complex and/or functional prototypes, SLS may be the better option. It is also recommended for use in mass-production situations. FDM, however, is better for simple proof-of-concept prototypes and can be a good point of entry into AM due to its relatively low cost.
SLS vs. FDM: Technology Comparison
Technology, in this case, refers to the equipment and tools used to produce a 3D-printed part. SLS systems have more complex technologies and processes than FDM (high-powered lasers, thermoplastic powders, and sintering). If you want simplicity, FDM would be the better option in terms of technology.
SLS vs. FDM: Material Comparison
Material has a big impact on the quality and surface finish of the part. SLS uses engineering thermoplastics such as Nylon 11 and Nylon 12. FDM uses standard thermoplastics such as PLA, ABS, and others.
SLS vs. FDM: Product Applications Comparison
The types of products you can create using SLS vs. FDM depend on their geometry and complexity as well as the material properties of the thermoplastic you select. When complexity isn't the goal, FDM is the better option.
SLS vs. FDM: Print Volume Comparison
SLS printers are smaller (up to 300 x 300 x 300 mm worth of printing volume) than FDM ones (up to 300 x 300 x 600 mm). If you need larger parts, FDM is the better option.
SLS vs. FDM: Surface Finish Comparison
The surface finishes of SLS parts serve some applications well even without post-processing (though others will require additional cleaning or finishing). FDM parts can appear rough because of the layers of filament used to form the part. This is what prevents FDM printers from reaching the same resolution as SLS.
SLS vs. FDM Cost Comparison
SLS systems are more expensive than FDM systems because of the complex technologies and materials involved. SLS systems start around $10,000 and can go as high as $100,000. Desktop FDM systems go for a few hundred dollars while industrial FDM printers start around $15,000.
What Are the Mutual Alternatives to SLS and FDM?
SLS and FDM printers are not the only AM options on the market. Alternatives include:
- Stereolithography (SLA)
- Digital light processing (DLP)
These two AM processes use special types of thermoplastics called photopolymers. These are liquid polymers cured by a UV laser (in SLA machines) or a projector (in DLP units) to form parts layer-by-layer.
What Are the Similarities Between SLS and FDM?
SLS and FDM exhibit some commonalities:
- Both SLS and FDM use thermoplastic materials to form parts.
- Both SLS and FDM are excellent for basic prototyping and proofs-of-concept.
- Both SLS and FDM can rapidly produce parts but cannot mass-produce them.
What Are the Other Comparisons for SLS Besides FDM?
A few other technologies bear similarities to SLS:
- SLS vs. MJF: MJF is comparable to SLS since both build up layers by fusing powder. However, the MJF machine uses an inkjet-style print head to apply a fusing agent to the sections of powder it needs to solidify. The whole space is then hit by infrared light to fuse the treated powder. MJF can also print much faster than SLS since entire layers are heated at once. For more information, see our article on SLS vs. MJF.
What are the Other Comparisons for FDM Besides SLS?
A similar alternative to FDM is the FFF process:
- FDM vs. FFF: FFF (fused filament fabrication) uses the same process as FDM. It uses a heated nozzle or extruder to apply layers of filaments to a flat printing bed. FFF, however, does not have FDM's heated chamber that helps control temperature. For more information, see our article on FDM vs. FFF.
Summary
This article summarized the differences between SLS and FDM 3D printing technologies.
To learn more about SLS vs. FDM and to help select the perfect technology for your products, contact a Xometry representative.
Xometry offers a full range of 3D printing services for your project needs. Visit our Instant Quote Engine to get a free, no-obligation quote in minutes.
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