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FDM vs. SLA vs. SLS
Additive manufacturing, or 3D printing, lowers costs, saves time, and transcends the limits of fabrication processes for product development. From concept models and functional prototypes in rapid prototyping to jigs, fixtures, or even end-use parts in manufacturing, 3D printing technologies offer versatile solutions in a wide variety of applications.
Over the last few years, high-resolution 3D printers have become more affordable, easier to use, and more reliable. As a result, 3D printing technology is now accessible to more businesses, but choosing between the various competing 3D printing solutions can be difficult.
Which technology is suitable for your particular application? What materials are available? What equipment and training do you need to get started? How about costs and return on investment?
In this article, we’ll take a closer look at the three most established plastic 3D printing processes today: fused deposition modeling (FDM), stereolithography (SLA), and selective laser sintering (SLS).
Trying to decide between FDM and SLA 3D printers? Check out our in-depth FDM vs. SLA comparison.
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Fused deposition modeling (FDM), also known as fused filament fabrication (FFF), is the most widely used form of 3D printing at the consumer level, fueled by the emergence of hobbyist 3D printers. FDM 3D printers build parts by melting and extruding thermoplastic filament, which a printer nozzle deposits layer by layer in the build area.
FDM works with a range of standard thermoplastics, such as ABS, PLA, and their various blends. The technique is well-suited for basic proof-of-concept models, as well as quick and low-cost prototyping of simple parts, such as parts that might typically be machined.
FDM parts tend to have visible layer lines and might show inaccuracies around complex features. This example was printed on a Stratasys uPrint industrial FDM 3D printer with soluble supports (machine starting at $15,900).
FDM has the lowest resolution and accuracy when compared to SLA or SLS and is not the best option for printing complex designs or parts with intricate features. Higher-quality finishes may be obtained through chemical and mechanical polishing processes. Industrial FDM 3D printers use soluble supports to mitigate some of these issues and offer a wider range of engineering thermoplastics, but they also come at a steep price.
FDM printers struggle with complex designs or parts with intricate features (left), compared to SLA printers (right).
Stereolithography was the world’s first 3D printing technology, invented in the 1980s, and is still one of the most popular technologies for professionals. SLA resin 3D printers use a laser to cure liquid resin into hardened plastic in a process called photopolymerization.
See how stereolithography works.
SLA parts have the highest resolution and accuracy, the clearest details, and the smoothest surface finish of all plastic 3D printing technologies, but the main benefit of SLA lies in its versatility. Material manufacturers have created innovative SLA photopolymer resin formulations with a wide range of optical, mechanical, and thermal properties to match those of standard, engineering, and industrial thermoplastics.
SLA parts have sharp edges, a smooth surface finish, and minimal visible layer lines. This example part was printed on a Formlabs Form 3 desktop SLA 3D printer (machine starting at $3,750).
SLA is a great option for highly detailed prototypes requiring tight tolerances and smooth surfaces, such as molds, patterns, and functional parts. SLA is widely used in a range of industries from engineering and product design to manufacturing, dentistry, jewelry, model making, and education.
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Selective laser sintering is the most common additive manufacturing technology for industrial applications, trusted by engineers and manufacturers across different industries for its ability to produce strong, functional parts.
See how selective laser sintering works.
SLS 3D printers use a high-powered laser to fuse small particles of polymer powder. The unfused powder supports the part during printing and eliminates the need for dedicated support structures. This makes SLS ideal for complex geometries, including interior features, undercuts, thin walls, and negative features. Parts produced with SLS printing have excellent mechanical characteristics, with strength resembling that of injection-molded parts.
SLS parts have a slightly rough surface finish, but almost no visible layer lines. This example part was printed on a Formlabs Fuse 1 benchtop SLS 3D printer (machine starting at $18,500).
The most common material for selective laser sintering is nylon, a popular engineering thermoplastic with excellent mechanical properties. Nylon is lightweight, strong, and flexible, as well as stable against impact, chemicals, heat, UV light, water, and dirt.
The combination of low cost per part, high productivity, and established materials make SLS a popular choice among engineers for functional prototyping, and a cost-effective alternative to injection molding for limited-run or bridge manufacturing.
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Each 3D printing technology has its own strengths, weaknesses, and requirements, and is suitable for different applications and businesses. The following table summarizes some key characteristics and considerations.
| Fused Deposition Modeling (FDM) | Stereolithography (SLA) | Selective Laser Sintering (SLS) | |
|---|---|---|---|
| Resolution | ★★☆☆☆ | ★★★★★ | ★★★★☆ |
| Accuracy | ★★★★☆ | ★★★★★ | ★★★★★ |
| Surface Finish | ★★☆☆☆ | ★★★★★ | ★★★★☆ |
| Throughput | ★★★☆☆ | ★★★★☆ | ★★★★★ |
| Complex Designs | ★★★☆☆ | ★★★★☆ | ★★★★★ |
| Ease of Use | ★★★★★ | ★★★★★ | ★★★★☆ |
| Pros | Low-cost consumer machines and materials Fast and easy for simple, small parts | Great value High accuracy Smooth surface finish Fast printing speeds Range of functional applications | Strong functional parts Design freedom No need for support structures |
| Cons | Low accuracy Low details Limited design compatibility | Sensitive to long exposure to UV light | Rough surface finish Limited material options |
| Applications | Low-cost rapid prototyping Basic proof-of-concept models | Functional prototyping Patterns, molds, and tooling Dental applications Jewelry prototyping and casting Modelmaking | Functional prototyping Short-run, bridge, or custom manufacturing |
| Print Volume | Up to 300 x 300 x 600 mm (desktop and benchtop 3D printers) | Up to 300 x 335 x 200 mm (desktop and benchtop 3D printers) | Up to 165 x 165 x 300 mm (benchtop industrial 3D printers) |
| Materials | Standard thermoplastics, such as ABS, PLA, and their various blends. | Varieties of resin (thermosetting plastics). Standard, engineering (ABS-like, PP-like, flexible, heat-resistant), castable, dental, and medical (biocompatible). | Engineering thermoplastics. Nylon 11, Nylon 12, and their composites. |
| Training | Minor training on build setup, machine operation, and finishing; moderate training on maintenance. | Plug and play. Minor training on build setup, maintenance, machine operation, and finishing. | Moderate training on build setup, maintenance, machine operation, and finishing. |
| Facility Requirements | Air-conditioned environment or preferably custom ventilation for desktop machines. | Desktop machines are suitable for an office environment. | Workshop environment with moderate space requirements for benchtop systems. |
| Ancillary Equipment | Support removal system for machines with soluble supports (optionally automated), finishing tools. | Washing station and post-curing station (both can be automated), finishing tools. | Post-processing station for part cleaning and material recovery. |
Ultimately, you should choose the technology that makes the most sense for your business. Prices have dropped significantly in recent years, and today, all three technologies are available in compact, affordable systems.
Calculating 3D printing costs does not end with upfront equipment costs. 3D printing material and labor costs have a significant influence on cost per part, depending on the application and your production needs.
Here’s a detailed breakdown by technology:
| Fused Deposition Modeling (FDM) | Stereolithography (SLA) | Selective Laser Sintering (SLS) | |
|---|---|---|---|
| Equipment Costs | Budget printers and 3D printer kits start at a few hundred dollars. Higher quality mid-range desktop printers start around $2,000, and industrial systems are available from $15,000. | Professional desktop printers start at $3,750, large-format benchtop printers at $11,000, and large-scale industrial machines are available from $80,000. | Benchtop industrial systems start at $18,500, and traditional industrial printers are available from $100,000. |
| Material Costs | $50-$150/kg for most standard and engineering filaments, and $100-200/kg for support materials. | $149-$200/L for most standard and engineering resins. | $100/kg for nylon. SLS requires no support structures, and unfused powder can be reused, which lowers material costs. |
| Labor Needs | Manual support removal (can be mostly automated for industrial systems with soluble supports). Lengthy post-processing is required for a high-quality finish. | Washing and post-curing (both can be mostly automated). Simple post-processing to remove support marks. | Simple cleaning to remove excess powder. |
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Prototypes of a ski goggles' frame printed with FDM, SLA and SLS technology (from left to right).
We hope this article has helped you focus your search for the best 3D printing technology for your application.
Explore our additional resources to master the intricacies of 3D printing, and dive deeper into each technology to learn more about specific 3D printing systems.
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Stereolithography (SLA) 3D Printing Guide
Stereolithography (SLA) 3D printing is the most common resin 3D printing process that has become vastly popular for its ability to produce high-accuracy, isotropic, and watertight prototypes and end-use parts in a range of advanced materials with fine features and smooth surface finish.
In this comprehensive guide, learn how SLA 3D printers work, why thousands of professionals use this process today, and how SLA printers can benefit your work.
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Stereolithography belongs to a family of additive manufacturing technologies known as vat photopolymerization, commonly known as resin 3D printing. These machines are all built around the same principle, using a light source—a laser or projector—to cure liquid resin into hardened plastic. The main physical differentiation lies in the arrangement of the core components, such as the light source, the build platform, and the resin tank.
Watch how stereolithography (SLA) 3D printing works.
SLA 3D printers use light-reactive thermoset materials called “resin.” When SLA resins are exposed to certain wavelengths of light, short molecular chains join together, polymerizing monomers and oligomers into solidified rigid or flexible geometries.
A graphic representation of the basic mechanics of stereolithography (SLA) 3D printing.
SLA parts have the highest resolution and accuracy, the sharpest details, and the smoothest surface finishes of all 3D printing technologies, but the main benefit of the stereolithography lies in its versatility.
Material manufacturers have created innovative SLA resin formulations with a wide range of optical, mechanical, and thermal properties to match those of standard, engineering, and industrial thermoplastics.
Advancements in 3D printing continue to change the way businesses approach prototyping and production. As the technology becomes more accessible and affordable and hardware and materials advance to match market opportunities and demands, designers, engineers, and beyond are integrating 3D printing into workflows across development cycles. Across industries, 3D printing is helping professionals cut outsourcing costs, iterate faster, optimize production processes, and even unlock entirely new business models.
Stereolithography 3D printing in particular has undergone significant changes. Traditionally, SLA 3D printers have been monolithic and cost-prohibitive, requiring skilled technicians and costly service contracts. Today, small format desktop printers produce industrial-quality output, at substantially more affordable price points and with unmatched versatility.
Compare stereolithography 3D printing to two other common technologies for producing plastic parts: fused deposition modeling (FDM) and selective laser sintering (SLS).
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See how to go from design to 3D print with the Form 3+ SLA 3D printer. This 5-minute video covers the basics of how to use the Form 3, from the software and materials to printing and post-processing.
Use any CAD software or 3D scan data to design your model, and export it in a 3D printable file format (STL or OBJ).
Each SLA printer includes software to specify printing settings and slice the digital model into layers for printing. Once setup is complete, the print preparation software sends the instructions to the printer via a wireless or cable connection.
More advanced users may consider specifically designing for SLA, or taking steps like hollowing parts to conserve material.
After a quick confirmation of the correct setup, the printing process begins and the machine can run unattended until the print is complete. In printers with a cartridge system, the material is automatically refilled by the machine.
An online Dashboard from Formlabs allows you to remotely manage printers, materials, and teams.
Once the printing is completed, parts require rinsing in isopropyl alcohol (IPA) to remove any uncured resin from their surface. After rinsed parts dry, some materials require post-curing, a process which helps parts to reach their highest possible strength and stability.
Finally, remove supports from the parts and sand the remaining support marks for a clean finish. SLA parts can be easily machined, primed, painted, and assembled for specific applications or finishes.
Post-curing is particularly important for functional resins for engineering, and mandatory for some dentistry and jewelry materials and applications.
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Engineers, designers, manufacturers, and more choose SLA 3D printing for its fine features, smooth surface finish, ultimate part precision and accuracy, and mechanical attributes like isotropy, watertightness, and material versatility.
Because 3D printing creates parts one layer at a time, completed prints may have variations in strength based on orientation of the part relative to the printing process, with different properties in X, Y, and Z axes.
Extrusion-based 3D printing processes like fused deposition modeling (FDM) are known for being anisotropic due to layer-to-layer differences created by the print process. This anisotropy limits the usefulness of FDM for certain applications, or requires more adjustments on the part geometry side to compensate for it.
Read our in-depth guide about FDM vs. SLA 3D printers to learn how they compare in terms of print quality, materials, applications, workflow, speed, costs, and more.
In contrast, SLA resin 3D printers create highly isotropic parts. Achieving part isotropy is based on a number of factors that can be tightly controlled by integrating material chemistry with the print process. During printing, resin components form covalent bonds, but layer to layer, the part remains in a semi-reacted “green state.”
While in the green state, the resin retains polymerizable groups that can form bonds across layers, imparting isotropy and watertightness to the part upon final cure.
On the molecular level, there is no difference between X, Y, or Z planes. This results in parts with predictable mechanical performance critical for applications like jigs and fixtures, end-use parts, and functional prototyping.
SLA printed parts are highly isotropic compared to those produced with fused deposition modeling (FDM).
Because they are isotropic, SLA printed parts like this jig from Pankl Racing Systems can withstand the variety of directional forces they undergo during high stress manufacturing operations.
SLA printed objects are continuous, whether producing geometries with solid features or internal channels. This watertightness is important for engineering and manufacturing applications where air or fluid flow must be controlled and predictable. Engineers and designers use the watertightness of SLA printers to solve air and fluid flow challenges for automotive uses, biomedical research, and to validate part designs for consumer products like kitchen appliances.
OXO relies on the watertightness of SLA printing to create robust functional prototypes for products with air or fluid flow, like this coffee maker.
Industries from dental to manufacturing depend on SLA 3D printing to repeatedly create accurate, precise components. For a print process to produce accurate and precise parts, multiple factors must be tightly controlled.
Compared to machined accuracy, SLA 3D printing is somewhere between standard machining and fine machining. SLA has the highest tolerance of commercially available 3D printing technologies. Learn more about understanding tolerance, accuracy, and precision in 3D printing.
The combination of the heated resin tank and the closed build environment provides almost identical conditions for each print. Better accuracy is also a function of lower printing temperature compared to thermoplastic-based technologies that melt the raw material. Because stereolithography uses light instead of heat, the printing process takes place at close to room temperature, and printed parts don't suffer from thermal expansion and contraction artifacts.
An example from the dental industry comparing a scanned component with the original CAD geometry, demonstrating the ability to maintain tight tolerances across an SLA printed part.
Low Force Stereolithography (LFS) 3D printing houses the optics inside a Light Processing Unit (LPU) that moves in the X direction. One galvanometer positions the laser beam in the Y direction, then directs it along across a fold mirror and parabolic mirror to deliver a beam that is always perpendicular to the build plane, so it is always moving in a straight line to provide even greater precision and accuracy, and allows for uniformity as hardware scales up to larger sizes, like Formlabs larger format SLA printer Form 3L. The LPU also uses a spatial filter to create a crisp, clean laser spot for greater precision.
The characteristics of individual materials are also important for ensuring a reliable, repeatable print process.
Formlabs Rigid Resin has a high green modulus, or modulus before post-curing, which means it’s possible to print very thin parts with precision and a lower chance of failure.
SLA printers are considered the gold standard for smooth surface finish, with appearances comparable to traditional manufacturing methods like machining, injection molding, and extrusion.
This surface quality is ideal for applications that require a flawless finish and also helps reduce post-processing time, since parts can easily be sanded, polished, and painted. For example, leading companies like Gillette use SLA 3D printing to create end-use consumer products, like 3D printed razor handles in their Razor Maker platform.
Leading companies like Gillette use SLA 3D printing to create end-use consumer products, like the 3D printed razor handles in their Razor Maker platform.
Z-axis layer height is commonly used to define the resolution of a 3D printer. This can be adjusted in between 25 and 300 microns on Formlabs SLA 3D printers, with a trade-off between speed and quality.
In comparison, FDM and SLS printers typically print Z-axis layers at 100 to 300 microns.
However, a part printed at 100 microns on an FDM or SLS printer looks different from a part printed at 100 microns on an SLA printer. SLA prints have a smoother surface finish right out of the printer, because the outermost perimeter walls are straight, and the newly printed layer interacts with the previous layer, smoothing out the staircase effect. FDM prints tend to have clearly visible layers, whereas SLS has a grainy surface from the sintered powder.
The smallest possible detail is also much finer on SLA, given 85 micron laser spot size on the Form 3+, in comparison with 350 microns on industrial SLS printers, and 250–800 micron nozzles on FDM machines.
While FDM 3D printed parts tend to have visible layer lines and might show inaccuracies around complex features, parts printed on SLA machines have sharp edges, a smooth surface finish, and minimal visible layer lines.
SLA resins have the benefit of a wide range of formulation configurations: materials can be soft or hard, heavily filled with secondary materials like glass and ceramic, or imbued with mechanical properties like high heat deflection temperature or impact resistance.
Material range from industry-specific, like dentures, to those that closely match final materials for prototyping, formulated to withstand extensive testing and perform under stress.
Rigid 10K Resin is a highly glass-filled material for industrial parts that need to withstand significant load without bending, including applications like injection molding.
In some cases, its this combination of versatility and functionality that leads to companies to initially bring resin 3D printing in-house. After finding one application solved by a specific functional material, it’s usually not long before more possibilities are uncovered, and the printer becomes a tool for leveraging the diverse capabilities of various materials.
For example, hundreds of engineers in the Design and Prototyping Group at the University of Sheffield Advanced Manufacturing Research Centre (AMRC) rely on open access to a fleet of 12 SLA 3D printers and a variety of engineering materials to support highly diverse research projects with industrial partners like Boeing, Rolls-Royce, BAE Systems, and Airbus.
The team used High Temp Resin to 3D print washers, brackets, and a sensor mounting system that needed to withstand the elevated, and leveraged Durable Resin to create intricate custom springy components for a pick and place robot that automates composites manufacturing.
Engineers at the AMRC use a fleet of 12 SLA 3D printers and a variety of engineering materials to print custom parts for diverse research projects, like brackets for a pick and place robot (top), and mounts for sensors in a high-temperature environment (bottom).
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SLA 3D printing accelerates innovation and supports businesses across a wide range of industries, including engineering, manufacturing, dentistry, healthcare, education, entertainment, jewelry, audiology, and more.
Rapid prototyping with 3D printing empowers engineers and product designers to turn ideas into realistic proofs of concept, advance these concepts to high-fidelity prototypes that look and work like final products, and guide products through a series of validation stages toward mass production.
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Manufacturers automate production processes and streamline workflows by prototyping tooling and directly 3D printing custom tools, molds, and manufacturing aids at far lower costs and lead times than with traditional manufacturing. This reduces manufacturing costs and defects, increases quality, speeds up assembly, and maximizes labor effectiveness.
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Digital dentistry reduces the risks and uncertainties introduced by human factors, providing higher consistency, accuracy, and precision at every stage of the workflow to improve patient care. 3D printers can produce a range of high-quality custom products and appliances at low unit costs with superior fit and repeatable results.
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Affordable, professional-grade desktop 3D printing helps doctors deliver treatments and devices customized to better serve each unique individual, opening the door to high-impact medical applications while saving organizations significant time and costs from the lab to the operating room.
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3D printers are multifunctional tools for immersive learning and advanced research. They can encourage creativity and expose students to professional-level technology while supporting STEAM curricula across science, engineering, art, and design.
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High definition physical models are widely used in sculpting, character modeling, and prop making. 3D printed parts have starred in stop-motion films, video games, bespoke costumes, and even special effects for blockbuster movies.
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Jewelry professionals use CAD and 3D printing to rapidly prototype designs, fit clients, and produce large batches of ready-to-cast pieces.
Digital tools allow for the creation of consistent, sharply detailed pieces without the tediousness and variability of wax carving.
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Hearing specialists and ear mold labs use digital workflows and 3D printing to manufacture higher quality custom ear products more consistently, and at higher volumes for applications like behind-the-ear hearing aids, hearing protection, and custom earplugs and earbuds.
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Many companies start using 3D printing via outsourcing to service bureaus or labs. Outsourcing production can be a great solution when teams require 3D printing only occasionally, or for one-offs that require unique material properties or applications. Service bureaus can also provide advice on various materials and offer value-added services such as design or advanced finishing.
The main downsides of outsourcing are cost and lead time. Often, outsourcing is a gateway to bringing production in-house as needs ramp up.
One of the greatest benefits of 3D printing is its speed compared to traditional manufacturing methods, which quickly diminishes when an outsourced part takes multiple days or even weeks to arrive. With growing demand and production, outsourcing also rapidly becomes expensive.
Because of the rise of affordable industrial-quality 3D printing, today, more and more companies choose to bring 3D printing in-house right away, vertically integrating into existing shops or labs, or in the workspaces of engineers, designers, and others who could benefit from translating digital designs into physical parts or who are involved in small batch production.
Small format, desktop SLA 3D printers are great when you need parts quickly. Depending on the number of parts and printing volume, investment into a small format 3D printer can break even within months. Plus, with small format machines, it’s possible to pay for just as much capacity as a business needs and scale production by adding extra units as demand grows.
Using multiple 3D printers also creates the flexibility to print parts in different materials simultaneously. Service bureaus can still supplement this flexible workflow for larger parts or unconventional materials.
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Fast turnaround time is a huge advantage to owning a desktop 3D printer. When working with a printing bureau, lead times, communication, and shipping all create delays. With a desktop 3D printer like the Form 3+, parts are in-hand within hours, allowing designers and engineers to print multiple parts in one day, helping to iterate faster and drastically reduce product development time and quickly test mechanisms and assemblies avoid costly tool changes.
Owning a desktop 3D printer results in significant savings over 3D printing service bureaus and traditional machining, as these alternatives rapidly becomes expensive with growing demand and production.
For example, to fulfill tight production deadlines, a process engineer and team at Pankl Racing Systems introduced SLA 3D printing to produce custom jigs and other low-volume parts directly for their manufacturing line. While in-house SLA was initially met with skepticism, it turned out to be an ideal substitute to machining a variety of tools. In one case, it reduced lead time for jigs by 90 percent—from two to three weeks to less than a day—and decreased costs by 80-90 percent.
| Cost | Lead Time | |
|---|---|---|
| In-House SLA 3D Printing | $9–$28 | 5–9 hours |
| CNC Machining | $45–$340 | 2–3 weeks |
| Outsourced 3D Printing | $51–$137 | 1–3 weeks |
Pankl Racing Systems significantly reduced lead times and costs by 3D printing custom jigs in-house.
With small format machines, it’s possible to pay for just as much capacity as a business needs and scale production by adding extra units as demand grows.
Using multiple 3D printers also creates the flexibility to print parts in different materials simultaneously.
The Design and Prototyping Group at the University of Sheffield Advanced Manufacturing Research Centre (AMRC) runs an open-access additive manufacturing station with a fleet of 12 Form 2 stereolithography (SLA) 3D printers for hundreds of engineers working on diverse projects across the site.
Formlabs offers two high precision SLA 3D printing systems, a growing library of specialized materials, intuitive print preparation and management software, and professional services—all in one package.
To continue exploring SLA 3D printing, start with feeling the quality of SLA for yourself: Request a free sample 3D printed part in your choice of material to be mailed straight to your door.
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3D printer comparison in 2020
A variety of 3D printing technologies are available on the market today. Getting to know the nuances of each helps you understand what you can expect from the final models and decide which technology is right for you.
Stereolithography (SLA) and digital light processing (DLP) are the two most common 3D printing technologies using resins. 3D printers that use resin as consumables have become very popular due to their ability to produce highly accurate, isotropic and waterproof prototypes and models with high detail and smooth surfaces.
While these technologies used to be complex and prohibitively expensive, today's compact desktop SLA and DLP printers produce industrial quality parts at an affordable price and offer tremendous application flexibility through a wide range of materials.
Both of these processes selectively expose liquid polymer to a light source: an SLA laser, a DLP projector, forming very thin, hard layers of plastic that fold into a solid object. Although the principle of operation of these technologies is very similar, they can give significantly different results.
In this detailed guide, we will explain the features of these two 3D printing processes and see how they differ in terms of resolution, accuracy, print volume, speed, workflows, etc.
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Desktop stereolithography 3D printers contain a resin tank with a transparent bottom and a non-adhesive surface that serves as a base for the liquid resin to solidify, allowing the newly formed layers to be gently peeled off.
The printing process begins with the platform lowered into the resin tank, leaving a free space corresponding to the height of the layer between the platform or the last finished layer and the bottom of the tank. The laser beam is fed to two mirror galvanometers, with the help of which it enters the desired coordinates on a series of mirrors. This allows a focused beam of light to be fed upwards through the bottom of the tank, under the influence of which the polymer layer hardens.
Then the hardened layer is separated from the bottom of the tank, and the platform rises higher, and liquid polymer enters the freed space.
This process is repeated until printing is complete.
The Form 3 and Form 3L Low Force Lithography (LFS) stereolithography technology is a new step in the development of stereolithographic 3D printing.
In LFS-based 3D printers, the optical components are located in the Light Processing Unit (LPU). Inside the LPU, a galvanometer positions the high-density laser beam in the y-direction, passes it through a spatial filter, and directs it into a deflecting and parabolic mirror to ensure that the beam always remains perpendicular to the plane of the platform, ensuring print accuracy and reproducibility.
As the LPU moves in the X direction, the printed model is gently separated from the flexible bottom of the tank, which greatly reduces the forces on the models during the printing process.
LFS-based 3D printing greatly reduces the stress placed on parts during the printing process by using a flexible reservoir and linear illumination to deliver incredible surface quality and print accuracy.
This advanced stereo lithography technology features higher surface quality and print accuracy. The lower print tear force also allows the creation of lightweight support structures that can be detached without force, and the method itself opens up great opportunities for the further development of advanced production-ready materials. Learn more about stereolithographic 3D printing
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Desktop DLP printers use a resin tank with a transparent bottom and a platform that descends into the tank to layer upside down models. In this they are no different from stereolithographic 3D printers.
The difference between them is the light source. DLP-based 3D printers use a digital screen to project the image of the layer onto the entire platform, causing all the desired dots to solidify at the same time.
Light is reflected on a digital micromirror screen (DMD), a dynamic mask consisting of microscopic mirrors that are located in a matrix on a semiconductor chip. The rapid switching of these tiny mirrors between lenses that direct light to the bottom of a tank or radiator determines the coordinates at which the liquid polymer must solidify in order to form the current layer.
Because the projector is a digital screen, each layer's image is made up of square pixels, resulting in a three-dimensional layer of rectangular cubes called voxels.
When it comes to 3D printer specifications, resolution is the focus, but it often leads to confusion. The basic units of the SLA and DLP processes are different forms, making it difficult to compare printers by numbers alone.
In 3D printing, there are three dimensions to consider: two planar 2D dimensions (X and Y) and a third vertical Z dimension, which is used for 3D printing.
The resolution of the Z measurement is determined by the thickness of the layer that the 3D printer can print.
Printers based on SLA and DLP technology have one of the best Z resolutions of any other process, allowing you to print layers with minimal thickness. Typically, users can set the layer height to between 25-300µm, allowing developers to trade-off between level of detail and speed.
In DLP printers, XY resolution is determined by the pixel size, the smallest detail that the projector can reproduce in a single layer. It depends on the resolution of the projector (the most common is Full HD (1080p)) and its distance from the optical glass. Therefore, most desktop DLP printers have a constant XY resolution of 35 to 100 microns.
In stereolithographic 3D printers, the XY resolution is determined based on the size of the laser spot and the number of steps that can be used to control the beam. For example, a Form 3 3D printer based on LFS technology has a laser with a spot size of 85 μm, but due to the constant line scanning process, the laser can move at a smaller step, and the printer can consistently print models with an XY resolution of 25 μm.
Resolution itself is often only an indicator of vanity. It gives some idea of the performance, but does not necessarily directly correspond to the accuracy and quality of the print.
Learn more about resolution in 3D printing in our detailed guide.
Since 3D printing is an additive process, violations can potentially occur in every layer. The process of forming layers affects the level of accuracy and correctness of each layer. Accuracy and accuracy depend on many factors: 3D printing process, materials, software settings, post-processing, etc.
In general, SLA and DLP printers are among the most accurate. Differences in print accuracy are often more noticeable between printers from different manufacturers than between the technologies themselves.
For example, entry-level SLA or DLP printers may use off-the-shelf projectors, lasers, or galvanometers, and their manufacturers strive to achieve optimum performance from these parts. Professional SLA and DLP printers (such as Formlabs Form 3) have a special optical system that is adjusted according to the needs of users.
Precision is critical for parts such as mouth guards (left) and surgical guides (right).
Precision is critical for parts such as mouth guards (left) and surgical guides (right).
Equally important is calibration. When using DLP projectors, manufacturers face uneven distribution of light on the platform and optical lens distortion, which means that the size and shape of the pixels in the middle and at the edges are different. Stereolithographic 3D printers use the same light source for all parts of the model, ensuring uniformity, but they still need to be carefully calibrated to avoid distortion.
Even a 3D printer with the best components and the best degree of calibration can produce different results depending on the consumables used. Resin parameters have to be changed to ensure the best quality, but they may not be available for new materials that have not been properly tested with the appropriate 3D printer model.
What conclusion can be drawn from this? Knowing only the technical characteristics, it is impossible to get a complete picture of the quality.
The best way to evaluate a 3D printer is to study the models printed on it or ask the manufacturer to make a test model for your project.
DLP printers have an inverse relationship between resolution and working volume. The resolution depends on the projector, which determines the number of pixels/voxels available. If you move the projector closer to the optical glass, the pixels will become smaller and the resolution will increase, but the working area will be limited.
Some manufacturers install multiple projectors side by side or use a 4K high-definition projector to increase the working area, but this increases the cost significantly. The price of such models is much higher than other desktop 3D printers.
Therefore, DLP printers are usually optimized for specific purposes. Some of them have a smaller workspace and allow you to produce in high resolution such small and detailed models as jewelry, while others can print larger parts, but with a lower resolution.
The stereolithography process is inherently more scalable because the print volume of an SLA printer is independent of model resolution. A single model can be of any size and resolution, and can be placed anywhere on the workspace. This allows you to print large high-resolution 3D models or large batches of finely detailed models to increase printer performance.
Another hurdle to increasing print volume in both SL and DLP printers is the release force. When printing large models, the forces applied to them increase exponentially as the cured layer separates from the reservoir.
With LFS printing, the flexible film at the base of the resin reservoir gently peels off when the platform pulls the model up, greatly reducing stress on the model. This unique feature has dramatically increased print volume in the first affordable large-format stereolithography printer, the Form 3L.
Form 3L is the first affordable 30 x 33.5 x 20cm large format 3D lithography 3D printer.
compared to solutions based on other technologies. When we talk about differences, in most cases they are only visible on very small parts and models with a high degree of detail.
Because 3D printers print in layers, finished models often have noticeable horizontal lines. And due to the fact that digital light processing technology uses rectangular voxels, the effect of vertical lines can also be observed.
DLP printers use rectangular voxels to render images, which can result in vertical lines. In this image, the vertical voxel lines are shown as they appear when printed (left), highlighted for better visibility (right).
Since voxels are rectangular, they affect the shape of the curved edges. Let's draw an analogy with creating a round shape from a LEGO constructor - the edges will have a stepped shape both along the Z axis and on the X-Y plane.
Due to the rectangular shape of the voxels, curved edges appear jagged. Removing visible voxels and layer lines requires post-processing such as sanding.
Layer lines are virtually invisible when printed with LFS-based 3D printers. As a result, surface roughness is reduced, resulting in a smooth surface, and when using transparent materials, models with greater transparency.
When talking about the speed of 3D printing, it is important to consider not only the printing speed itself, but also the productivity.
The overall print speed of 3D printers based on SLA and DLP technologies is approximately the same. Since the projector exposes each layer as a whole, the speed of DLP 3D printing is uniform and depends only on the height of the model, while SLA 3D printers laser shape each part. As practice shows, as a result, stereolithographic 3D printers become comparable in speed or even faster when printing one small or medium model, while DLP printers are faster at printing large solid models or several models that almost completely fill the space of the platform.
But do not forget that in printers based on DLP technology, there is an inverse relationship between resolution and working volume.
A small DLP printer can quickly print small models or high-resolution (small) batches of small models, but print volume limits model size and device performance. Another high volume device can produce larger models, or batches of smaller models, faster but at lower resolution than a stereolithographic printer.
With a stereolithographic 3D printer, all this can be done on one machine. At the same time, users can decide what they want to optimize in each case: resolution, speed or performance.
DLP printers use rectangular voxels to render images, which can result in vertical lines. In this image, the vertical voxel lines are shown as they appear when printed (left), highlighted for better visibility (right).
Stereolithographic 3D printers have higher print volumes, batch production, and overnight printing for increased productivity.
| 100 microns | 200 microns |
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| 100 microns | 200 microns |
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| 100 Microns | 200 Microns |
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Stereolithographic 3D printers have higher print volumes, batch production, and overnight printing of models, increasing productivity.
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As with accuracy, differences in workflows and available materials are more printer specific than technology.
Most SLA and DLP printers are plug and play and allow easy replacement of platforms and resin tanks. Some more sophisticated models come with a cartridge system to automatically refill the reservoir with liquid resin, requiring less attention and making it easier to print at night.
Some printers come with their own software for preparing 3D models for printing (for example, PreForm for Formlabs stereolithographic 3D printers), while other manufacturers offer ready-made standard solutions. Different software tools have different features, such as PreForm allows you to customize the printing process with one click, powerful tools for optimizing the density and size of supporting structures, adjustable layer thickness, and features to save materials and time.
Fortunately, the software can be downloaded and tested before purchasing a 3D printer.
As with precision, differences in workflows and available media are more printer dependent than technology.
3D printers can work with a wide range of polymer materials for different applications.
One of the main advantages of polymer-based 3D printing is the large number of materials from which models can be made for various purposes. Polymers with different compositions have a variety of characteristics: they can be soft or hard, contain additives such as glass and ceramics, or have special mechanical properties such as high bending temperature under load or impact resistance.
But at the same time, the range of supported materials depends on the specific model of the 3D printer, so we recommend that you check this information with the manufacturer before making a purchase.
SLA and DLP prints require post-processing after printing. First, the models must be washed in solvent to remove excess resin.
In some cases, such as models made from engineering and biocompatible materials, final polymerization is also required. For stereolithographic 3D printers, Formlabs offers solutions to automate these steps, saving you time and effort.
Finally, 3D models printed on supporting structures require the removal of such structures. This must be done manually - the process is similar for both SLA and DLP printers. LFS-based 3D printers use lightweight support structures with very small contact points, allowing for easy release with minimal marks.
Interactive
Need some help figuring out which 3D printing material you should choose? Our new interactive material wizard helps you make the right material decisions based on your application and the properties you care the most about from our growing library of resins.
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We hope that after understanding the differences in technologies and print results, it will be much easier for you to choose the 3D printer that best suits your needs and workflow.
To learn more about the next generation of stereolithographic 3D printers, check out the Form 3 and Form 3L devices based on LFS technology.
Would you like to see the resulting quality with your own eyes? Order a print sample, which will be delivered directly to your office.
Request a free print sample
SLA Technology. How SLA 3D printing works.
Hello everyone, 3DTool is with you!
Today we will look at the basic principles of the SLA technology. After reading this article, you will understand the main points of the printing process using this technology, the advantages and disadvantages of this method 3D printing .
On our website, you can find a list of 3D printers working on technology SLA , at this link: Catalog of 3D printers printing using SLA / DLP technology
Technology 3 D printing SLA
Stereolithography (SLA) is an additive manufacturing process that achieves its result by means of resin polymerization.
In SLA printing, the object is created by selectively curing a polymer resin, layer by layer, using an ultraviolet (UV) laser beam. The materials used in SLA printing are photosensitive thermoset polymers that come in liquid form.
SLA is known as the first 3D printing technology : its inventor patented this technology back in 1986 . When you need to print parts with very high precision or a smooth surface, the SLA comes to the rescue. In this case, it is the most cost-effective and efficient technology 3D printing . The best results can be achieved only if the operator of the equipment on which the printing process takes place is familiar with the technology and some of the nuances. That is, he has the necessary qualifications.
SLA shares many characteristics with Direct Light Processing (DLP ), another photopolymerization technology. For simplicity, both technologies can be considered equal.
SLA printing process
Here's how the process works:
1) 2) 3)
1) A platform is placed in the tank with liquid photopolymer, at the same height from the resin surface.
2) The UV laser then selectively cures the required areas of the photopolymer resin according to a predetermined algorithm.
The laser beam is focused on a given path using a set of mirrors called galvos. Then the entire cross-sectional area of the model is illuminated. Therefore, the resulting part is completely solid.
3) When one layer is finished, the platform moves to a safe distance and the mixing foot inside the tub mixes the resin.
This process is repeated until the part is printed. After printing, the part is not fully cured and requires further post-processing under the UV lamp .
At the end of UV illumination, the part acquires very high mechanical and thermal properties.
The liquid resin solidifies through a process called photopolymerization: during solidification, the monomer carbon chains that make up the liquid resin are activated by an ultraviolet laser and become solid, creating strong, inextricable bonds with each other.
The photopolymerization process is irreversible, and there is no way to convert the resulting parts back into a liquid state. When heated, they will burn, not melt. This is because the materials that are produced with SLA technology are made from thermoset polymers, as opposed to thermoplastics that FDM uses.
Scheme of work SLA printer
Printer Features SLA
On SLA systems, most print settings are set by the manufacturer and cannot be changed.
The only inputs are the layer height and the part orientation ( last, locates the supports ).
The typical layer height in SLA printing ranges from 25 to 100 micron .
The lower the layer height, the more accurately the complex geometry of the model will be printed, but at the same time the printing time and the likelihood of failure will increase. The layer height of 100 microns is suitable for most common geometries and is the golden mean.
Another important parameter for the operator is the size of the platform. It depends on the type of SLA printer. There are two main types: orientation top to bottom and orientation from bottom to top .
In the first case, the laser is above the tank, and the part is face up. The platform sits at the very top of the resin vat and moves down after each layer is sintered.
Schematic SLA top-down printer
In " bottom up " layout on SLA printers , the light source is placed under the resin tank (see picture above) , and the part is built upside down.
The tank has a transparent bottom with a silicone coating that allows the beam of light to pass through but prevents the cured resin from sticking. After each layer, the cured resin separates from the bottom of the tank as the platform moves up. This is called the sintering step .
Schematic SLA bottom-up printer
The orientation " bottom to top " is mostly used in desktop printers such as Formlabs. The " top - down " orientation is used in the industrial SLA printer .
Printers SLA " bottom-up " are easier to manufacture and operate, but the size of the possible print will be smaller, since the forces applied to the part during the sintering stage can cause printing to fail.
Top-down printers, on the other hand, can print very large parts without much loss in accuracy. The wide possibilities of such systems naturally cost more.
The following are the main characteristics and differences between the two orientations:
| "From top to bottom " | |
| Pros: | |
| lower cost | |
| Wide market availability | |
| Minuses: | |
| Small platform size | |
| Smaller range of materials | |
| Requires additional post-processing due to extensive use of supports | |
Popular brands:
FORMLABS
Printable size: Up to 145 x 145 x 175 mm
Typical layer height and print accuracy: 25 to 100 µm and ± 0.
5% (lower limit: ± 0.010 to 0.250 mm) respectively
| "Upwards" | |
| Pros: | |
| Very large platform | |
| Faster Print Time | |
| Minuses: | |
| High price | |
| Qualified operator required | |
| Material change involves emptying the entire tank | |
Popular brands:
PRISMLAB
Printable area: Up to 1500 x 750 x 500 mm
Typical layer height and print accuracy: 25 to 150 µm and ± 0.15% (lower limit ± 0.010 to 0.030 mm) respectively
Support during printing 3 D
Supports are always required at Print SLA .
Structural structures are printed from the same material as the part and must be manually removed after printing.
Part orientation determines the location and amount of supports. It is recommended that the part be oriented so that surfaces that require maximum quality do not come into contact with supports.
In different types of SLA printers, support is used in different ways:
For top - down printers , support requirements are the same as FDM . They are essential for accurate printing of overhangs and bridges ( the critical overhang angle is typically 30 degrees ).
The part can be oriented in any position and is usually printed flat to minimize the number of supports and the total number of layers.
In printers like " from bottom to top " everything is more complicated. Overhangs and bridges also need to be supported, but minimizing the cross-sectional area of each layer is the most important criterion.
Forces applied to the part during the sintering step can cause it to come off the platform. These forces are proportional to the cross-sectional area of each layer.
For this reason, the parts must be oriented at an angle, and minimizing supports here is not a primary concern.
On the left - a detail oriented on the SLA printer "from top to bottom" (support minimization).
On the right is a part oriented on the SLA printer "from the bottom up" (minimizing the cross-sectional area).
Removing supports for an SLA printed part
Curl
One of the biggest problems with the accuracy of parts made with SLA , is twisting. This problem is similar to the deformation in FDM when materials shrink.
During curing, the resin shrinks slightly when exposed to the printer's light source. When shrinkage is significant, large internal stresses develop between the new layer and the previously cured material, causing the part to twist.
Adhesion (sintering) between layers
SLA printed parts have isotropic mechanical properties. This is due to the fact that one pass UV beam is not enough to completely cure the liquid resin.
Further passes help the previously hardened layers to fuse together. In fact, in the SLA of printing, curing continues even after the printing process is completed.
To achieve the best mechanical properties, parts printed using this technology should be post-cured by placing them in a chamber under intense ultraviolet radiation ( and sometimes at elevated temperatures ).
This greatly increases the hardness and heat resistance of SLA but does not make it any stronger. Rather the opposite.
For example.
Test specimens printed with standard clear resin on a SLA desktop printer have, after curing, almost 2 times 's tensile strength ( 65 MPa compared to 's 38 MPa) after curing.
Can operate under load at higher temperatures ( 58 degrees Celsius compared to 's 42 degrees), but their elongation at break is less than half ( 6.2% compared to 's 12%).
If you leave the part in the sun, then nothing good will come of it.
Prolonged exposure to ultraviolet radiation has a detrimental effect on physical properties and appearance. The part may curl, become very brittle, and change color.
For this reason, before using the part, it is recommended to apply a spray of transparent acrylic paint resistant to UV radiation .
SLA media
SLA Printing Materials is available in liquid resin form. Price per liter of resin varies greatly - ranges from $50 for standard material to $400 for specialty materials such as casting or dental resin.
Industrial systems offer a wider range of materials than desktop systems SLA printers, which give the designer more control over the mechanical properties of the printed part.
SLA materials ( thermosets ) are more brittle than materials made using FDM or SLS ( thermoplastics ) and for this reason SLA parts are not typically used for functional prototypes that will be subjected to significant stress. However, new advances in materials development may change this in the near future.
The following table lists the advantages and disadvantages of the most commonly used resins:
| Material | Features |
| Standard resin | + Smooth surface Relatively fragile part |
| transparent resin | + Transparent material - Requires post-processing for Presentable appearance |
| casting resin | + Used to create mold templates + Low ash after burnout |
| Rigid or durable resin | + ABS-like or PP-like mechanical properties - Low thermal resistance |
| High temperature resin | + High temperature resistance + Used for injection molding · - High price |
| dental resin | + Biocompatible + High abrasion resistance · - High price |
| Rubber-like resin | + Rubber-like material - Poor printing accuracy |
Post-processing SLA 3D printing
Parts printed with SLA technology can be processed to a high quality using various methods such as sanding and polishing, staining and mineral oil treatment.
Widely developed articles about post-processing can be found on the Internet.
Transparent resin housing cover for electronics in various finishes. From left to right: removal of the main support, wet sanding, UV irradiation, acrylic and polishing
SLA advantages and disadvantages
Pros:
-
SLA 3D printers can produce parts with very high dimensional accuracy and complex geometries.
-
The parts will have a very smooth surface, making them ideal for visual prototypes, for example.
-
Special materials are available such as clear, flexible and cast resins.
Cons:
-
Parts printed using SLA technology tend to be fragile and not suitable for functional prototypes.
-
The mechanical properties and appearance of these parts deteriorate over time.
They are adversely affected by exposure to sunlight. -
Supports and post-processing when printing are always required.
The main characteristics of the SLA are shown in the table:
materials
Photopolymer resins (thermosetting
materials)
Dimensional accuracy
± 0.5% (lower limit: ± 0.10 mm) - domestic
± 0.15% (lower limit ± 0.01 mm) - industrial
typical size
print area
Up to 145 x 145 x 175 mm - for desktop printers
Up to 1500 x 750 x 500 mm - for industrial
Total layer thickness
25 - 100 µm
Support
Always required
(Needed to make an accurate part)
Total
-
SLA print is best for producing visual prototypes with a very smooth surface and very fine detail.
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