Fused Deposition Modeling vs. Selective Laser Sintering – Key Differences

One common question we get is about which additive manufacturing technology best suits a part. That's especially the case when the manufacturing methods possess some fundamental similarities, which is the case with Fused Deposition Modeling (FDM) and Selective Laser Sintering (SLS).

FDM and SLS are among the most popular 3D printing technologies available. Both use various polymer materials and can create everything from prototypes to end-use parts. However, critical differences between the two technologies mean they have different applications.

This article explains the advantages and disadvantages of both technologies, so you'll know exactly what to choose for your next project.

An SLS part made with PA 12.

Key Advantages of SLS and FDM 

• FDM is typically faster and the basic materials are cheaper than SLS – but some high-performance materials can be expensive

• SLS offers higher strength, ideal for high-stress or high-load applications – such as end-use parts and functional prototypes

• SLS offers better dimensional accuracy, making it better suited for complex geometries

• FDM provides a wider material choice

How FDM and SLS Technologies Work

The first big difference between FDM and SLS is the underlying basis of the technology. In short, SLS is a powder bed-based technology that uses a laser to melt the parts. Alternatively, FDM uses a thermoplastic filament that is melted and extruded through a nozzle.

This significant difference impacts the materials, accuracy, and mechanical characteristics of parts made with either technology.

The FDM Printing Process

The SLS Printing Process

FDM vs. SLS Materials

With SLS being powder-based and SLS relying on filaments, the available materials are different despite both being polymers.

Low-cost home-based 3D printers use FDM technology, so there's a misconception that most of the materials technology offer low performance. While FDM offers "basic" low-cost materials, there are strong and versatile filaments suited for industrial use.

FDM parts made with Acrylonitrile butadiene styrene (ABS) materials.

Some of these filaments include:

• Acrylonitrile butadiene styrene (ABS)-based polymers are quite versatile, with variants suited for everything from electronics to medical devices

• ULTEM 1010 and ULTEM 9085 are high-performance materials that are also flame retardant. Both offer high levels of strength, making them ideal for challenging applications

• See more of the available FDM materials

SLS relies on powder-based polyamides (PA). There's a wide range of varieties available ideal for a range of industrial applications.

• PA 12 is the standard SLS material, offering high strength and stability, chemical resistance, and biocompatibility at competitive prices

• PA 12 Aluminum Filled: Adding aluminum t PA gives it excellent dimensional stability at high temperatures, but with the light weight of a plastic

• PA 12 Flame Retardant: A chemical flame retardant is added to PA12, making the material suited for electronic components and aircraft interiors.

• See more of the available SLS materials

FDM vs. SLS Strength

The strength of a printed part varies depending on several factors, such as the material used, print orientation, layer thickness, and more. Both SLS and FDM offer high-strength materials. However, SLS has the advantage when it comes to strength.

SLS’s sintering process eliminates the need for support structures and creates a more solid part, while FDM’s high strength materials are comparitively expensive and ansiotrophic (meaning the parts have a higher rate of failure if they aren’t optimally oriented).  

FDM vs SLS Appearance

SLS parts are printed in white (or sometimes gray), making them easier to color. After removing the support and excess powder, the printed appearance is typically grainy. Smoothing, tumbling, and other SLS post-processing options can remedy this.

An SLS part made from PA 12 that was tumbled for smoothness.

FDM parts, however, can be printed in a range of colors. This is especially useful for cosmetic prototypes. After the parts are printed, print lines are visible. Due to that, it's normal to opt for finishes like sanding or vapor smoothing.

Want to improve your FDM designs? We have the guide for you.

One thing to note about FDM: it's especially prone to the "staircase effect." When this happens, each printed layer becomes visible. Instead of the expected smooth surface, the damaged surface resembles a staircase. This effect can be mitigated by having upward-facing surfaces rather than sideways-facing surfaces. This is also something to be aware of with SLS, but the effect is far smaller with this technology.

The staircase effect is an important consideration for FDM parts

When to Use FDM vs SLS

So, when should you use SLS vs. FDM? That depends entirely on your application, as both these technologies have their own advantages.

For Cosmetic Prototyping: FDM

FDM might not have the same dimensional accuracy as SLS, but that's no problem for cosmetic prototyping. FDM is the technology of choice for visual representations that don't need to be functional.

For Short Lead Times: FDM (with a slight advantage)

Both technologies ensure parts can get into your hands quickly. However, FDM has a very small edge when it comes to lead time. An SLS part using standard materials takes seven days on the MakerVerse platform. FDM has a lead time of six days.

For Functional Prototypes: SLS

SLS offers strong parts, which makes it ideal for functional applications that undergo stress, wear, and tear. Furthermore, the dimensional accuracy of SLS makes it ideal such applications.

For End-Use Parts: SLS

All the reasons why SLS is usually better for functional prototypes apply to end-use parts. While FDM parts are often used for industrial purposes, SLS is much more common.

Lower Upfront Cost: FDM

Material prices can vary greatly, as high performance materals are comparitively expensive compared to basic materials. However, creating parts with basic FDM materials is typically cheaper. This is one of the reasons why the technology is so opular for visual prototypes. Alternatively, SLS offers a way to create parts with good mechnical properties at a compeitive price.

SLS vs FDM Cheat Sheet

Compare SLS and FDM today. Upload your part and get an instant quote for both technologies.