Fused Deposition Modeling vs. Selective Laser Sintering

One common question is which additive manufacturing technology best suits apart. That’s especially true when the manufacturing methods possess some fundamental similarities, which is the case with Fused Deposition Modeling (FDM), also known as fused filament fabrication, 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.

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

• The printing process of FDM involves layer-by-layer deposition of melted material, while SLS uses a laser to sinter powdered material, eliminating the need for support structures.

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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 heated nozzle.

This heated nozzle is critical to the FDM process, enabling the deposition of molten material onto the build platform to create parts layer by layer. FDM technology utilizes various types of thermoplastic polymers, such as PLA and ABS, which are essential for achieving precise and intricate part designs.

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 FDM relying on filaments, the available materials are different despite being polymers. SLA, on the other hand, uses a digital light projector to cure liquid resin layer by layer, producing high-resolution parts with intricate details and smooth finishes.

Low-cost home-based 3D printers use FDM technology, so there’s a misconception that most materials technology offers low performance. While FDM provides “basic” low-cost materials, there are strong and versatile filaments suited for industrial use.

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

Some of these filaments include:

• Acrylonitrile butadiene styrene (ABS)-based polymers are pretty 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). Various varieties are available, which are ideal for multiple 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

SLA 3D printing also offers the advantage of using the same material for both the main print and support structures. This approach eliminates the need for separate support materials, streamlines the printing process, and simplifies post-processing, as the support can be removed without the complexities of differing material properties.

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, but SLS has the advantage in strength.

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

SLS technology simplifies post-processing and enhances efficiency by using unsintered powder as support, making it ideal for both prototyping and final production.

FDM vs. SLS Appearance

SLS parts are printed in white (or sometimes gray), making them easier to color. The printed appearance is typically grainy after removing the support and excess powder. 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 is that 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 this technology’s impact is far smaller.

The staircase effect is an essential consideration for FDM parts

In SLA 3D printing, UV light is used to cure photopolymer resin after printing. This post-processing step ensures complete curing, which is essential for the final strength and durability of the printed components.

Prototyping and Production Applications

Additive manufacturing technologies are versatile, serving both prototyping and production needs.

FDM is a popular choice for prototyping due to its speed and cost-efficiency, allowing for rapid iteration and development of visual models.

In contrast, SLA and SLS are often preferred for production applications where high accuracy and superior mechanical properties are essential. SLS, in particular, is widely used in demanding industries such as aerospace, automotive, and healthcare, where the performance of parts is critical.

SLA also finds its niche in sectors like dental and jewelry, where precision and fine details are crucial. Each technology has its strengths, making them suitable for different stages of product development and various industry requirements.

Cost and ROI

The cost of adopting additive manufacturing technologies can vary significantly based on the type of technology, print volume, and material properties.

FDM printers are generally the most affordable, with entry-level models available for a few hundred dollars, making them accessible for small businesses and hobbyists.

In contrast, SLA and SLS printers come with a higher price tag, ranging from a few thousand to tens of thousands of dollars. However, the investment in these technologies can be justified by the benefits they offer, such as reduced material waste, increased productivity, and enhanced product quality.

Conducting a thorough cost-benefit analysis is crucial to determine the return on investment (ROI) for each technology, ensuring that the chosen solution aligns with the specific needs and budget of the project.

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 advantages.

For Cosmetic Prototyping: FDM

FDM might have a different dimensional accuracy than SLS, but that’s fine 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 tiny 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 vital parts, which makes it ideal for functional applications that undergo stress, wear, and tear. Furthermore, its dimensional accuracy makes it suitable for such applications. SLS printing is particularly advantageous for producing strong, functional parts and complex geometries.

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 vary greatly, as high-performance materials are comparable to primary materials. However, creating parts with basic FDM materials is typically cheaper. This is one of the reasons why the technology is so popular for visual prototypes. Alternatively, SLS offers a competitive price for creating parts with good mechanical properties.

In FDM, support structures are necessary to ensure successful 3D printing outcomes, whereas SLS eliminates the need for dedicated support structures by utilizing unsintered powder.