Selective Laser Sintering (SLS) and Fused Deposition Modeling (FDM) are like the Peyton Manning and Cam Newton of 3D printing—two of the best quarterbacks in the league, one about ten years older than the other (SLS was commercialized in around 1980 and FDM around 1990), and currently both at the top of their game. SLS and FDM are often compared because they both deliver similar materials and engineering-grade thermoplastics which give them the ability to serve functional and production manufacturing applications. Even though SLS and FDM are equally capable of producing strong, durable parts, their divergent delivery mechanisms make certain geometries and applications better suited for one or the other. Learning the advantages and differences between technologies will help lead you to the best process for your project.
You’ll see positive results on internal cavities with both FDM and SLS when the features are accessible to a finisher removing supports. FDM offers break-away support which is manually removed by hand and soluble support which dissolves in a water-based solution (ideal for internal cavities). SLS parts use the unsintered powder as support during the process, which can be easily brushed away post-build. For difficult to access internal features, you’ll find more success using SLS regardless of material choice because excess powder can be easily brushed or blown away from cavities. Tough-to-reach internal features can be more difficult with FDM, especially with non-soluble support materials that need to be manually removed.
One of the largest build platforms in the industry is the Fortus 900mc (FDM technology) which measures 36”x24”x36”. The largest SLS platform is the EOS P700 series at 24”x14”x20”, but building large parts can be problematic, depending on the geometry. FDM manufactures flat areas with ease while flat parts built with SLS would likely warp if the walls are too thin. SLS is often better suited for curved large parts with rounded features. However SLS can successfully produce a large flat part if ribbing is included to reinforce the area.
Both technologies offer materials specifically formulated for withstanding high temperatures, but FDM’s ULTEM™ resin materials hold the title for highest heat deflection temperature with ULTEM™ 9085 resin at HDT 307° F @ and ULTEM™ 1010 resin at HDT 415° F. ULTEM™ resin is also UL94 V-0 rated and passes the FAR. 25.853 60-second vertical burn test. However, SLS’s high-temp materials aren’t far off with Nylon 12 PA at HDT 187° F and Nylon 12 CF at HDT 260° F and Nylon 11 FR and Nylon 12 FR passing the FAR 25.853 60-second vertical burn test.
Selective Laser Sintering has a clear advantage in isotropic mechanical properties with near consistency in X, Y, and Z. SLS is also better positioned in terms of flexibility and a family of Nylons with better elongation properties than any other FDM materials. When it comes to impact strength, both technologies are far above the other plastics processes in the field, but SLS has select materials with slightly higher impact strength than most FDM materials (SLS Nylon 12 PA, NyTek 1200 PA, and NyTek 1200 FR are 4.12ft-lb/in and FDM PC-ABS is 3.7 ft-lb/in).
Like Manning and Newton, SLS and FDM each excel at different aspects of the game, but both are unarguably two of the strongest players. For more helpful tips on deciding on the best process for your application and geometry, read 7 Questions to Ask When Choosing a 3D Printing Technology.
