3D printing, also known as additive manufacturing, is a revolutionary technology that has transformed the way we design and manufacture objects. It works by creating a three-dimensional object from a digital model, typically by laying down many thin layers of a material in succession. This technology has found applications in a wide range of industries, from aerospace and automotive to healthcare and fashion.

In the consumer-focused desktop 3D printer market, the two main types of 3D printing technologies that have gained significant popularity due to their unique capabilities are Fused Deposition Modeling (FDM) — otherwise known as Fused Filament Fabrication (FFF) — and various types of vat photopolymerization technology, perhaps the most famous of which is Stereolithography (SLA). Both of these technologies have their own set of advantages and disadvantages, and their suitability varies depending on the specific requirements of the project at hand.

Understanding the working principles, capabilities, and limitations of these two different technologies is crucial for anyone looking to leverage 3D printing for their prototyping and manufacturing needs. This article therefore looks at FDM vs SLA in terms of cost, benefits, materials, and applications.

Understanding FDM

An FDM 3D printer printing yellow filament

Fused Deposition Modeling (FDM) is the most widely used 3D printing technology in terms of machines sold, being used by industrial manufacturers and hobbyists alike. It works by extruding a thermoplastic filament, which is heated to its melting point and then deposited layer by layer to create a three-dimensional object.[1] The filament is fed from a spool through a moving, heated printer extruder head and onto the build area below.

The materials used in FDM 3D printing are thermoplastic polymers that come in a filament form. These FDM materials include Acrylonitrile Butadiene Styrene (ABS), Polylactic Acid (PLA), and Polyethylene terephthalate glycol-modified (PETG) at the lower end of the scale and high-performance engineering materials like PEEK at the higher end (though most ordinary printers don’t have the power to print such materials). Common printing materials have their own unique properties and are suitable for different applications. For instance, ABS is known for its high strength and durability, making it ideal for functional prototypes and end-use parts, while PLA is notably easy to print thanks to its low melting point.

FDM has several advantages that make it a popular choice for 3D printing. It is known for its ease of use, cost-effectiveness, and the ability to use a variety of materials. However, it also has its limitations. Print quality on consumer-level machines is limited, and the parts may have visible layer lines. Additionally, unlike certain 3D printing technologies such as selective laser sintering (SLS), FDM requires the use of support structures for overhanging areas, and these need to be manually removed post-printing.

Recommended reading: FFF vs FDM: Is There Any Difference?

The FDM Printing Process

The FDM printing process begins with a 3D model that is sliced into layers using specialized software. This software converts the 3D model into a series of thin layers and produces a G-code file that contains instructions for the FDM 3D printer. The G-code file guides the movements of the printer head to deposit the material in the correct locations.

The printer heats the thermoplastic filament to a temperature just beyond its glass transition temperature. The heated filament is then extruded through a nozzle onto the build platform. The nozzle moves in the X and Y directions, depositing the material layer by layer according to the instructions in the G-code file. After a layer is completed, the build platform moves down (or in some printers, the extruder head moves up), and the next layer is deposited. This process continues until the entire object is printed.

The final product created by FDM printing is a solid object that has been built up from successive layers of material. The object may require some post-processing, such as the removal of support structures and smoothing of the surface to reduce the appearance of layer lines. The quality and characteristics of the final product can be influenced by various factors, including the type of material used, the layer thickness, the printing speed, and the temperature settings.

Applications of FDM

Fused Deposition Modeling (FDM) has found widespread use across a variety of industries due to its versatility, cost-effectiveness, and the ability to work with a range of materials. It is primarily used for prototyping across these industries, but it can also be useful for spare parts, repairs, and even production parts.

In the automotive industry, FDM is used to create functional prototypes, end-use parts, and custom jigs and fixtures — Volkswagen being one major company deploying FDM for this purpose. For instance, the ability to print with high-strength materials like ABS and Nylon makes FDM a suitable choice for producing durable components that can withstand the rigors of automotive testing.

The medical field also benefits from FDM technology. Custom surgical guides, anatomical models for surgical planning, and even patient-specific prosthetics can be created using FDM. Materials like PLA are often used in these applications due to their biocompatibility.

In the realm of consumer goods, FDM is used to rapidly prototype new product designs, create custom parts, and even manufacture end-use products. In footwear, for example, sportswear brand Adidas has used 3D printing to create midsoles for sneakers. In general, the wide range of available FDM materials, each with different properties, allows for a high degree of customization based on the specific needs of the product.

In education, FDM printers serve as an invaluable tool for teaching students about design, engineering, and manufacturing. The relatively low cost and ease of use of FDM printers make them an accessible technology for schools and universities.

Understanding SLA

An SLA 3D printer printing a transparent resin part

Stereolithography (SLA) is another prominent 3D printing technology that operates on a completely different principle compared to FDM. SLA is part of the category of vat photopolymerization resin 3D printing methods, which use a light source to cure and solidify a liquid resin, layer by layer, to form a solid object.[2] With SLA specifically, the light source is usually a UV laser, which is directed by a set of galvanometers that rapidly deflect the laser beam across the build platform. Digital light processing (DLP), a similar process, uses a projector instead of a laser.

The materials used in SLA are photosensitive thermoset polymers that come in a liquid resin form. These SLA resins are transformed from a liquid to a solid state when exposed to a specific wavelength of light. The properties of the final product can vary greatly depending on the type of resin used. There are a wide variety of resins available, each with different properties, such as flexibility, strength, temperature resistance, and optical clarity.

Advantages of SLA include its high resolution and accuracy, which allows for the creation of high-quality parts with fine details and smooth surfaces. However, SLA also has its limitations. The materials used in SLA are generally more expensive than FDM filaments, and the post-processing can be more labor-intensive. Furthermore, build volumes tend to be small, making the process limited to small printed parts.

Recommended reading: How Do Resin Printers Work? SLA, DLP & More

The SLA Printing Process

The SLA printing process begins with a vat of liquid resin. A build platform is lowered into the vat, and a UV laser traces the first layer of the object onto the surface of the liquid resin, causing it to harden. Once the first layer is complete, the build platform moves up, and the process is repeated for the next layer. As with FDM, printer control comes from a sliced part design which is converted into printer instructions.

The final product created by the SLA printer is a solid object that has been built up from successive layers of cured resin. The object is typically attached to a support structure during printing to prevent deformation or displacement. After printing, the object requires post-processing, which includes removing the support structures, washing the object to remove excess resin, and curing the object under UV light to ensure complete solidification.

The quality and characteristics of the final product can be influenced by various factors, including the type of resin used, the layer thickness, the laser power, and the exposure time. By adjusting these parameters, it is possible to control the mechanical properties, dimensional accuracy, and surface finish of the printed object.

Applications of SLA

Stereolithography (SLA) has a wide range of applications across various industries, primarily due to its high precision and ability to produce parts with smooth finishes and intricate details.

In the medical and dental industries, SLA is extensively used due to its high precision and the availability of biocompatible resins. It is used to create dental models, surgical guides, and hearing aids. Detailed anatomical models can be created for pre-surgical planning, helping surgeons visualize complex procedures beforehand. A well-known user of SLA in this space is Align Technologies, the company behind Invisalign dental braces.

In the jewelry industry, SLA is used to create highly detailed and intricate designs. The high resolution of SLA allows for the creation of complex geometries and intricate patterns that would be difficult to achieve with traditional manufacturing methods. These models can then be used to create molds for casting precious metals.

In product design and manufacturing, SLA is used for rapid prototyping. Designers can quickly create a physical model of their design, allowing them to test the form, fit, and function of the product before moving to mass production. The smooth surface finish achieved with SLA also makes it ideal for creating prototypes for aesthetic and ergonomic evaluations.

In the field of education and research, SLA is used for creating accurate 3D models for study and demonstration. The high resolution and accuracy of SLA make it ideal for creating detailed models that accurately represent complex structures and systems.

FDM vs SLA: A Side-by-Side Comparison

SLA parts can provide better detail and surface finish

When comparing FDM vs SLA, it's essential to consider various factors such as cost, speed, precision, material options, and post-processing requirements. Each technology has its strengths and weaknesses.

FDM is often the preferred choice for projects that require a lower cost, faster printing times, and the ability to use a wide range of thermoplastic materials. (Printers with hard nozzles can also process composite materials containing non-plastic additives like chopped carbon fibers.) It is well-suited for producing functional prototypes, large parts, and objects that do not require a high level of detail or surface finish. FDM is also a good choice when the printed object needs to withstand higher temperatures or mechanical stress, as there are a variety of high-strength and high-temperature resistant filaments available.

On the other hand, SLA is ideal for projects that demand high precision, intricate details, and smooth surface finishes. In fact, researchers have found that the surface of roughness of SLA parts can be even lower than injection molded equivalents.[3] SLA is particularly useful for creating small, complex parts, such as jewelry, dental models, and highly detailed prototypes. However, it tends to be more expensive and slower than FDM, and the materials used are generally more costly. SLA is also a good choice when the printed object requires a level of transparency.

The choice between FDM and SLA also depends on the post-processing capabilities and requirements. FDM parts often require some amount of post-processing to improve the surface finish, while SLA parts require washing and curing after printing, which can be time-consuming and require additional equipment.

Recommended reading: What is 3D Printing: A Comprehensive Guide to its Engineering Principles and Applications

Conclusion

Understanding the differences between FDM and SLA 3D printing technologies is crucial for making informed decisions when selecting the most appropriate method for a specific project. Each technology has its unique strengths and limitations, making each one suitable for certain applications. By considering factors such as cost, time, precision, material properties, and post-processing requirements, users can choose the most suitable 3D printing technology for their specific needs and ensure the success of their projects.

Frequently Asked Questions (FAQs)

What is the main difference between FDM and SLA?

FDM uses a thermoplastic filament that is heated and extruded layer by layer to create a 3D object, while SLA uses a UV laser to cure and solidify a liquid resin, also layer by layer.

Which technology is more cost-effective, FDM or SLA?

Generally, FDM is more cost-effective due to the lower cost of materials and equipment. However, the specific cost-effectiveness depends on the project requirements and the materials used.

Which technology is better for creating highly detailed parts?

SLA is better suited for creating highly detailed parts due to its higher resolution and ability to produce smooth surface finishes.

Can both FDM and SLA print with a wide range of materials?

FDM can print with a wide range of thermoplastic filaments and composites, while SLA uses specially formulated photosensitive resins. FDM offers a slightly wider range of material possibilities.

What are the post-processing requirements for FDM and SLA?

FDM parts often require support removal and surface smoothing, while SLA parts require support removal, washing, and curing under UV light.

References

[1] Solomon IJ, Sevvel P, Gunasekaran J. A review on the various processing parameters in FDM. Materials Today: Proceedings. 2021 Jan 1;37:509-14.

[2] Yang Y, Li L, Zhao J. Mechanical property modeling of photosensitive liquid resin in stereolithography additive manufacturing: Bridging degree of cure with tensile strength and hardness. Materials & Design. 2019 Jan 15;162:418-28.

[3] Özdilli Ö. Comparison of the Surface Quality of the Products Manufactured by the Plastic Injection Molding and SLA and FDM Method. International Journal of Engineering Research and Development. 2021 Jun 6;13(2):428-37.