Comparing SLA Vs. FDM 3D Printing Technologies

Advances in 3D printing technology have occurred rapidly over the past few years. What was once a hobby for a few has become an essential tool across the design, engineering, and manufacturing sectors across many industries. Besides, 3D printers are now used as real workhorses rather than as a novelty incorporated to handle fast-paced situations, as was the case in the past. 3D-printed parts can even achieve impressive resolution and tolerances.

Among 3D printing methods, the two most popular are Fused Deposition Modeling (FDM) and Stereolithography (SLA). Both methods have deep roots in the 1980s, and while they share some production steps, they are fundamentally different processes.

Stereolithography (SLA) makes parts by curing a liquid photopolymer resin with a UV laser layer by layer. Similarly, Fused Deposition Modeling (FDM) makes parts by melting and extruding the plastic filament onto the build plate, layer by layer. In conclusion, the outputs (or products) differ from each other in important ways.

While rapid prototyping is the primary goal for both, the best option depends on the part’s shape and the prototype’s intended use. Choosing the best 3D printing technology can be daunting, as each has distinct advantages and disadvantages.

In this comprehensive guide, we will compare FDM and SLA (filament and resin) printers. Additionally, we will compare their print quality, materials, speed, costs, and workflows to help you determine which best suits your business needs.

What is FDM 3D Printing?

Fused Deposition Modeling (FDM), or filament-based 3D printing, is the most common consumer 3D printing method. It uses the familiar “hot-glue gun” method, in which melted plastic is applied to form parts. For many individuals, Fused Deposition Modeling (FDM) is their first introduction to 3D printing technology.

Moreover, FDM systems are common in K-12 schools and university maker spaces. In design, engineering, and manufacturing, project teams typically develop quick proof-of-concept models using FDM printers. The purpose of the proof-of-concept models is to help everyone agree on the design before moving to a more functional prototype phase.

FDM printers vary in size and price, and their relatively simple technology and workflow make them a lower risk for beginners. However, as you can imagine, most new technology comes with both advantages and disadvantages. Additionally, simplicity and low cost are disadvantages for part quality and performance.

Especially for functional parts that require water tightness, isotropic uniform strength, and smooth surfaces, SLA and SLS printers perform orders of magnitude better than FDM printers.

How Does FDM Work?

Fused Deposition Modeling (FDM) is one of the first 3D printing processes invented by Scott Crump, the co-founder of Stratasys. It’s really quite simple: think of it like an active hot glue gun. A thermoplastic filament is heated until it melts. The molten plastic is extruded through a nozzle, moving in the X and Y directions to deposit a thin layer on the build platform.

After the layer cools and solidifies quickly, the platform will lower slightly. The nozzle will then deposit the next layer, building the part along the Z-axis until the print is complete.

Advantages of FDM Compared to SLA

• FDM parts are typically sturdier than SLA parts because FDM uses thermoplastics, which are well-known and more durable than the photopolymers used in SLA.
• FDM benefits from a large user community, with access to pre-designed, FDM-optimized models and extensive support resources for troubleshooting common printing issues.

Disadvantages of FDM Compared to SLA

• FDM parts typically exhibit visible layer lines, which means they usually require post-processing to achieve the smooth surface finish common to SLA/resin-printed parts.
• FDM materials, while exhibiting high tensile strength, often produce anisotropic parts. Because of the relatively weak interlayer bonding, parts printed in the print direction are typically weaker than those printed in the layer direction.

What is SLA 3D Printing?

Stereolithography (SLA) was the first 3D printing technology developed in the 1980s. Although the first 3D printing technology, SLA, has been slower to gain popularity than FDM. That’s because of higher costs and a relatively complex printing process.

SLA printing also comes with the name “resin 3D printing”, which cures liquid resin into 3D form using a light source (layer by layer). SLA was initially used to refer to printers that used lasers as their light source.

However, laser SLA printers have slowly been replaced by digital light projectors (DLP) or light-emitting diodes (LED) in MSLA or LCD printers. Today, almost all resin printers are considered SLA printers, although SLA is typically used to refer to printers that use lasers.

SLA printers generate parts with smooth surfaces, tight tolerances, and very high dimensional accuracy, surpassing most other 3D printing methods.

Moreover, they are perfect for functional prototyping because they represent the look and feel of injection-molded parts. SLA’s high-quality surface finish and available materials make it suitable for manufacturing end-use products and tooling.

SLA materials differ from the typical thermoplastics used in FDM and SLS printing. One of SLA’s greatest strengths is its material flexibility. It is available as innovative photopolymer resins that offer a virtually limitless range of optical, mechanical, and thermal properties.

Manufacturers are producing new resins that emulate standard engineering plastics or fulfil specific needs, including flame-retardant, electrostatic-dissipative, and biocompatible materials. This variety, SLA’s accuracy, and high-quality surface finish have led to SLA parts being used across a wide range of industries. As a result, SLA is gaining popularity across a range of applications, including aerospace, automotive, personal and consumer goods, healthcare, and dentistry.

How Does SLA Work?

SLA utilizes photopolymer resins as its printing medium. Manufacturers cure these using strong ultraviolet (UV) light from a laser, the fundamental basis of the SLA method. The build platform floats in a vat of liquid resin. A laser above the vat, directed by mirrors, cures the resin and creates the part layer by layer.

The printer begins with printing support materials. Subsequently, the support is cemented to the platform and held in place (without disturbing the part) once the first layers are printed. The recoated blade applies a new resin layer after each cured layer. Supports and the part gradually build from the bottom up.

Advantages of SLA Compared to FDM

• SLA can achieve much higher resolutions and superior print quality compared to FDM.
• SLA can print parts faster than FDM while maintaining the same level of detail and accuracy.

Disadvantages of SLA Compared to FDM

• Compared to FDM, SLA printers and materials are much more expensive.
• SLA parts are typically weaker than FDM parts because photopolymer resins have lower mechanical strength than FDM thermoplastics.

Material Properties Comparison: SLA vs. FDM

Property	SLA	FDM (Industrial)
How it Works	Laser-cured photopolymer	Fused thermoplastic extrusions
Strength	2,500–10,000 psi (17.2–68.9 MPa)	5,200–9,800 psi (35.9–67.6 MPa)
Finish	Smooth surface finish, less visible layer lines	Layer lines are visible; post-processing is required for a smooth finish
Material Options	Thermoplastic-like photopolymers (ABS, PC, PP), True Silicone, Ceramic-like PerFORM MicroFine	Nylon, ABS, PEI (Ultem 9085, 1010), ASA, Markforged Onyx, ABSplus
Resolution	Normal, High, Micro	Low
Maximum Part Size	Normal: 29 x 25 x 21 in. (736 x 635 x 533 mm) High: 10 x 10 x 10 in. (254 x 254 x 254 mm) Micro: 5 x 5 x 2.5 in. (12 x 127 x 63.5 mm)	15.98 x 13.97 x 15.98 in. (406 x 355 x 406 mm)
Minimum Feature Size	Normal: X-Y: 0.010 in. (0.254 mm), Z: 0.016 in. (0.406 mm) High: X-Y: 0.005 in. (0.1016 mm), Z: 0.016 in. (0.406 mm) Micro: X-Y: 0.0025 in. (0.0635 mm), Z: 0.008 in. (0.203 mm)	0.0787 in. (2.0 mm)
Isotropy	Highly isotropic parts	Parts are anisotropic (stronger along the print direction)
Wall Thickness	Normal: 0.010 in. (0.254 mm) High: 0.004 in. (0.1016 mm) Micro: 0.0025 in. (0.635 mm)	0.0315 in. (0.8 mm)

SLA Vs. FDM: Comparison Breakdown

Each option has its advantages, ideal applications, and unique materials. In this side-by-side comparison, we will explore the key differences between SLA and FDM to help you select the right option for your application.

Technology

The differences between SLA and FDM technology are so great that it is not necessarily valid to compare them directly. FDM technology (and its associated printers) is so simple to use that anyone with generic technical skills can assemble these printers. SLA “machines,” on the other hand, require specialized knowledge and tools for setup and use. Additionally, SLA uses a laser to solidify resin upon exposure, while FDM relies on the material’s natural cooling.

Material

SLA uses liquid resin, which is often proprietary to specific printers. The resin comes in limited colours and material options. However, FDM offers a wider range of options and can include filaments with various colours and additives to enhance strength, such as carbon fibre. Similarly, most FDM printers can accept filaments from different suppliers, allowing for more options.

Product Applications

SLA technology is best suited for applications that prioritize fine detail over extreme structural strength. Thus, it is perfect for making jewellery moulds, display pieces, and visual prototypes.

Hobbyists and professionals more commonly use FDM technology for both functional and non-functional parts. Moreover, FDM materials are strong enough to create items such as jigs, brackets, and working prototypes.

Print Volume

FDM printers vary significantly in size. FDM printer build volumes range from small desktop machines to large printers capable of printing up to cubic meters. However, SLA printers have much smaller build volumes because they must contain liquid resin within the machine.

Surface Finish

Parts produced via SLA provide an excellent surface finish that is much smoother than that achievable with an FDM process. FDM prints typically exhibit visible layer lines and require post-processing, such as sanding or vapour smoothing (available only with certain materials).

Cost

SLA printers typically cost much more than FDM printers. This is primarily due to the cost of the resins and the UV laser, which must be highly precise to enable SLA to print at the quality it is known for. Entry-level FDM printers start at around $200, while SLA printers start at about $1295.

When to Use SLA vs. FDM

When choosing between SLA and FDM, consider the part’s function and the project budget. SLA is ideal for parts that require precise details and a design that matches the performance you expect from the moulded product. However, FDM produces more robust parts, and the material used for the FDM part is often identical to the final mould material. We sometimes choose to build an SLA prototype for presentations and an FDM part for functional testing because of its strength.

Here are the bottom-line essentials to help you make a choice:

Use SLA for

• High-precision, fine-detail applications such as fit-check prototypes and microfluidics.
• Surfaces with smooth finishes that require no post-processing are ideal for moulds or cosmetic prototypes.
• Short-term use cases where aesthetics and detail matter.

Use FDM for

• A great selection of thermoplastic materials and colours.
• Cost-effective prototypes that still provide durability.
• End-use parts such as custom jigs, fixtures, and other functional components.

Alternatives to SLA and FDM

Certainly, SLA and FDM aren’t the only 3D printing technologies. If you’re interested in options that don’t follow SLA or FDM, consider PolyJet or Carbon DLS for your application.

PolyJet operates by applying small droplets of liquid photopolymer resin, which is instantly cured by UV light. Additionally, during the printing process, the printer places “voxels” (3D pixels) accurately. 

The thickness of each voxel represents your layer thickness, typically about 30 microns. Consequently, the final prints are highly accurate 3D-printed parts. Moreover, PolyJet is economical and flexible, with a variety of durometers, making it a viable choice for prototyping, including over-moulded parts.

Carbon DLS leverages CLIP (Continuous Liquid Interface Production) technology, which uses the balance of light and oxygen to produce your parts. Using DLS, a light source is projected through an oxygen-permeable window onto the UV-curable resin in a reservoir.

As a sequence of projected UV images begins curing the part, the build platform rises to extract it. Subsequently, the entire system operates at high speed to produce durable, high-quality parts.

Conclusion