Navigation

1. Introduction
2. What Are Polymer 3D Printing Technologies?
3. What Is SLS 3D Printing?
4. What Is SLA 3D Printing?
5. Pros and Cons of SLS vs SLA
6. Which Is Better? SLS or SLA
7. Conclusion

Introduction

3D printing has completely changed how we make stuff. With just a click of a button, you can turn 3D designs into real, physical objects now. It’s opened up a whole new world of fast prototyping, custom manufacturing, and more.

When it comes to polymer 3D printing, key players are technologies like SLS (selective laser sintering), SLA (stereolithography), and FDM. Each brings unique strengths to the table. Interested in knowing more about the contrasts between SLS and FDM?

In this guide, we’ll look at the pros, cons, how they work, and material choices of SLS and SLA printing. The goal is to help you figure out which tech is right for your specific needs. Read on to learn how to pick between SLS vs SLA for your next project.

What Are Polymer 3D Printing Technologies?

Polymer 3D printing refers to additive manufacturing processes that use plastic materials to build 3D objects. SLS and SLA are two of the most common polymer technologies used today.

Both utilize lasers to selectively cure or fuse material layer-by-layer until the complete 3D object is formed. The laser precisely traces each cross-section of the model, solidifying the material as it goes along.

After one layer is finished, the build platform lowers, and a fresh layer of material is applied on top. The process repeats until the full model is complete. This enables the creation of complex geometries and internal features not possible with traditional manufacturing methods.

The key difference between SLS and SLA lies in the materials used and how they are processed. SLS uses plastic powder, whereas SLA uses liquid plastic resin. Let’s take a closer look at each of these technologies.

What Is SLS 3D Printing?

SLS stands for selective laser sintering. It’s one of the most common polymer powder bed fusion 3D printing processes.

With SLS, a laser selectively fuses fine plastic powder together layer-by-layer to build the 3D object. The powder is spread in thin layers across the build platform and heated to just below its melting point. The laser then traces the cross-section of the model in that layer, sintering the powder together to create a solid form.

Once a layer is complete, the build platform lowers, and a new layer of powder is applied on top. The partially completed model sits just below the surface of the powder bed. This provides support for overhangs and complex geometries as the part is being built up layer-by-layer.

The excess powder remains loose around the model and can be reused for future prints. This enables efficient material utilization. Once printing is finished, the object is removed from the powder bed and any excess material is cleaned off.

SLS is popular for its ability to produce durable plastic parts with good mechanical properties. A range of thermoplastic materials can be processed, including nylons, polycarbonate, TPU, and more.

What Is SLA 3D Printing?

SLA stands for stereolithography. It’s one of the most common vat photopolymerization 3D printing processes.

With SLA, a laser beam traces the cross-section of a model in a vat of liquid photopolymer resin. The laser cures and solidifies the resin, transforming the liquid plastic into a solid 3D object layer-by-layer.

Resin 3D printers contain a build platform that lowers progressively into the resin vat as each layer is completed. Once a layer is traced, the build platform lifts slightly to allow fresh resin to flow beneath and prepare for the next layer.

Excess liquid resin remains in the vat and can be reused for future prints. Once the print is finished, the 3D model is removed from the vat and cured further. Support structures are removed and any excess resin is cleaned off the model.

SLA is valued for its ability to produce detailed 3D prints with smooth surface finishes. The process enables intricate designs, fine features, and transparency effects. A range of photopolymer resins are available, from rigid to flexible.

Pros and Cons of SLS vs SLA

When deciding between SLS vs SLA, it’s important to weigh the unique advantages and limitations of each process. Here’s an overview of the key pros and cons:

SLS 3D Printing:

• Pros: Durable parts, good mechanical properties, variety of materials like Nylon and TPU, no supports needed, efficient material use.
• Cons: Lower resolution, porous surfaces, material limitations, slower print speeds, higher equipment costs.

SLA 3D Printing:

• Pros: Smooth surface finish, high accuracy and detail, ideal forprototypes, broad material selection including clear resins.
• Cons: Resin is more expensive, more post-processing work, brittle materials, limited build size, materials degrade over time.

Technology Comparison of SLS vs SLA

When it comes to the hardware and technology behind each process, there are some notable differences between SLS and SLA 3D printers:

• SLS printers utilize a laser to selectively sinter material across a powder bed. SLA uses a laser to selectively cure resin point-by-point.
• Powder bed fusion printers like SLS require material dispensing systems to apply fresh layers of powder. SLA printers use a lifting platform and resin flow to bring new material layers into place.
• Powder bed systems necessitate recoating blades or rollers to spread new powder evenly. This can lead to some variability.
• SLA printers offer higher resolution and accuracy given the precise point-by-point laser tracing process.
• SLS systems allow larger build volumes since an entire powder bed is utilized. SLA build sizes are limited by VAT size.
• SLS printers have higher upfront costs given the material handling systems required. SLA printers are more accessible for desktop use cases.
• SLS machines have additional requirements like inert gas flow and powder recycling systems. SLA printers focus on the laser system and resin management.
• Powder bed fusion technology like SLS can involve more variability between systems. SLA benefits from the precise nature of point-by-point processing.

These technology differences make each process suitable for different applications depending on factors like part size, accuracy, and budget.

Material Comparison of SLS vs SLA

When it comes to materials for 3D printing, SLS and SLA offer different selections and capabilities:

• SLS utilizes plastic powder materials like Nylon, TPU, PEBA, and PC. More engineering-grade thermoplastics are possible.
• SLA uses liquid photopolymer resins. More common resins include standard, durable, flexible, castable, and high-temperature resins. Specialty resins provide advanced properties.
• Material options for SLS printing have expanded in recent years, but there are still fewer materials compared to SLA.
• SLA resins produce higher resolution and more detailed parts than SLS powder. However material properties are generally weaker than robust SLS thermoplastics.
• Parts printed on SLS machines exhibit good mechanical characteristics like impact resistance, ductility, and thermal resistance.
• Isotropic properties of SLA resins allow smooth surface finishes and transparency. Anisotropic powder layers make SLS parts more porous.
• SLS materials are limited by what can be reliably processed in powder form. Liquid SLA resins offer wider formulation possibilities.
• Unused powder from SLS printing can be recycled for future prints. SLA resin degrades over time with exposure to light.

Understanding these material differences allows proper selection for mechanical, visual, or other requirements.

Finished Product Comparison of SLS vs SLA

The different processes, technologies, and materials used in SLS and SLA 3D printing result in different finished part characteristics:

• SLS parts exhibit a matte, porous finish with a grainy texture from the layered powder material. SLA products have a smooth, clean finish from liquid resin.
• Parts made on SLS machines tend to have higher strength and thermal resistance than SLA-printed components.
• Powder bed fusion methods like SLS produce anisotropic properties and parts can be weaker in the Z-axis. SLA results in more isotropic finished products.
• Unpolished SLS parts have a dusty appearance from excess powder sticking to the surface. SLA parts need supports removed and the resin washed off when finishing.
• SLS can leave small divots or dips on downward-facing surfaces where the powder is trapped. SLA resin self levels as it cures for smooth bottoms.
• With thin features or walls, SLS parts can exhibit some warpage or shrinkage effects. SLA resin cures evenly for consistency.
• SLS can generate more reliable, durable parts for functional prototypes or end-use production. SLA provides extremely high accuracy and resolution for visualization.

Surface Finishes Comparison of SLS vs SLA

The surface finish and quality of printed parts are one of the biggest differences between SLS vs SLA:

• SLS parts exhibit a grainy, sandy finish from layers of sintered powder. The matte, porous texture feels rough to the touch.
• SLA produces very smooth print surfaces since liquid resin self-levels and cures evenly layer-by-layer. The resulting finish appears glossy and clean.
• Unpolished SLS parts have a textured, dusty appearance. The loose powder sticks to part surfaces and edges.
• While SLA parts need some light sanding and polishing for a perfect finish, SLS requires heavy post-processing to achieve smoothness.
• Powder residue on SLS prints can obscure fine features. The resin cures cleanly over delicate details and intricate geometries.
• SLA’s ultra-smooth finishes show subtle curves, embossed text, holes, or any exposed face with high clarity.
• The point-by-point tracing process of SLA 3D printing reduces layer line visibility compared to the layer-by-layer sintering of SLS.
• Isotropic properties of SLA resins prevent directional textures or visual defects associated with the build orientation.

Which Is Better? SLS or SLA

With such different capabilities and applications, is one 3D printing technology definitively better than the other? Here are some key considerations:

• For prototyping, SLA is preferable for accuracy, fast print speeds, smooth finishes, and a variety of resins. SLS excels at larger components like functional prototypes needing durability.
• For end-use production, SLS is superior for its engineering-grade materials, high mechanical strength, heat/chemical resistance, and efficient production.
• For complex geometries with thin features or negative space, SLA’s crisper detail and self-leveling resin prevent defects like warpage.
• When post-processing time and labor are prohibitive, SLS has a strong advantage since parts just need powder removed versus SLA’s more intensive finishing.
• For small, highly detailed parts where resolution is critical, SLA is the better choice. SLS capabilities start to diminish below a certain size threshold.
• When budget is a primary factor, SLA printers provide an affordable entry point for desktop systems. Industrial SLS equipment requires a greater investment.
• If material selection is paramount, SLA offers the widest range of photopolymer resins to meet specialized needs. SLS materials are still maturing.

Ultimately, determining if SLS or SLA is the better 3D printing technology depends wholly on the application requirements like accuracy, material properties, budget, speed, and more. Both have advantages that make them suitable for different needs.

Conclusion

SLS and SLA represent two of the most common polymer 3D printing technologies in use today. At a high level, SLS utilizes powder bed fusion to selectively sinter plastic powder, while SLA uses photopolymerization to cure liquid resin layer-by-layer.

Key factors like process, technology, materials, part finish, feature resolution and more differentiate these approaches and make them suitable for unique applications. For large functional prototypes, end-use components requiring strength and heat resistance, and efficient batches of production parts, SLS excels.

For extremely high accuracy, smooth surface finishes, delicate features, quick turnaround, and wide material selection, SLA is likely the better choice.

Considering your specific needs around budget, speed, part size, geometry, mechanical properties, and intended use will clarify which technology provides the right capabilities. Both SLS and SLA have evolved into faster, higher-quality processes than ever before, opening new possibilities across industries like automotive, aerospace, medical, dental, consumer products, and more. Leveraging the right polymer 3D printing technology allows you to transform digital designs into physical reality.

As you navigate the world of 3D printing technologies, considering each one’s unique capabilities is crucial. Besides SLS and SLA, another notable contender in this landscape is FDM 3D Printing.