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. On the other hand, FDM machines 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 are: that they operate via different processes, require different post-processing steps, and machine ownership has significantly different barriers to entry. Because SLS machines selectively fuse layers from a bed of powder, dedicated support structures aren’t needed as this powder base also supports part features while they print. This eases the creation of accurate complex geometries, interior features, and undercuts. Post-processing SLS is straightforward, typically just needing a brief cleaning step after removal from the build chamber. SLS parts have excellent mechanical properties similar to those of plastic-injected parts. However, these benefits come at a high barrier to entry cost, with even the most basic machines costing thousands of dollars. FDM is often more cost-effective than SLS, especially when it comes to creating very large parts. It can still produce parts at similar speeds, albeit with lower resolution and detail.
In this article, we will dive deeper into the differences and similarities between SLS and 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 generally more expensive than FDM, SLS can create better-resolution parts with excellent mechanical properties and intricate geometries while remaining accurate. The image below is an example of an SLS 3D printing station at Xometry:
To learn more, see our article on SLS (Selective Laser Sintering).
Industrial SLS 3D printers at Xometry
Image Credit: Xometry
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.
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 has a more limited selection of materials than FDM, generally constrained to polyamides.
- Warping and over-sintering can occur on large, flat surfaces and small holes of SLS-printed parts.
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 industrial FDM 3D printers used by Xometry:
To learn more, see our guide on FDM 3D Printing.
Industrial FDM 3D printers at Xometry
Image Credit: Xometry
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 have very large build volumes, making large parts multiple feet across possible.
Listed below are the disadvantages of FDM vs. SLS:
- The lower resolution of FDM makes it less desirable for small and/or detailed parts.
- Slower print times mean FDM isn’t ideal for large batches or production runs.
- FDM parts require support structures when printing overhanging features, resulting in more involved post-processing steps and a higher risk of build failure or defects.
Easy to use technology
Wide material selection
Use for proof-of-concept prototypes
Up to 13"x13"x20" (typical)
Up to 24"x36"x36" (typical)
Use for functional prototypes and end-use parts
Need for supports during printing
Handling of complex or highly-detailed geometries
* The suitability of one technology over another can depend highly on your projects unique specifications and needs. Consult with Xometry about your project to determine the best solution.
In this case, technology 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.
Material can have a big impact on the characteristics, performance, and surface finish of a part. SLS is generally limited to nylon materials such as PA11 and PA12, with some filled variants available. FDM can use a wide array of standard thermoplastics, such as PLA, ABS, and polycarbonate, to name a few.
SLS may be the better option if your project requires complex and/or functional prototypes. It is also recommended for use in mass-production scenarios. FDM, however, is great for simple proof-of-concept prototypes and can be a good point of entry into AM due to its relatively low cost.
The types of products you can create using SLS vs. FDM depend on their geometry and complexity and the material properties of the thermoplastic you select. When complexity isn't the goal, FDM is the better option. If you want greater detail and end-use parts made of nylon, SLS can be an excellent choice.
SLS printers typically have smaller print volumes (e.g., 13" x 13" x 20") compared to FDM, which can produce parts as large as 24″ x 36″ x 36″ using commercial machines. If you need large parts, FDM has more room to work with. However, it should be noted with SLS printing, parts can be stacked and nested within each other, making it well suited for printing a high number of smaller parts in a single build.
The surface finishes of SLS parts are generally better thanks to the laser-sintering process. The standard SLS finish resembles a sugar cube texture and can serve some applications well, even without post-processing (though others will require additional finishing). FDM parts can appear rough because of the comparatively thicker layers of filament used to form the part, which creates a stair-stepping effect. This is what prevents FDM printers from reaching the same resolution as SLS.
SLS systems are more expensive than FDM systems because of the complex technologies and materials involved. SLS systems start at around $10,000 and can go as high as $100,000 or more. Desktop or hobbyist-level FDM systems can be purchased for a few hundred dollars, while industrial FDM printers start around $15,000. Part costs between commercial SLS and FDM are comparable for smaller components, although FDM will generally be cheaper for larger parts, especially when dimensions exceed 12 inches.
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 resins called photopolymers. These are liquid polymers cured by a UV laser (in SLA machines) or with light projection (in DLP) to form parts layer-by-layer.
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.
- SLS and FDM can rapidly produce parts but are generally unsuitable for the mass production of thousands of pieces.
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.
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.
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.
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