Gone are the days of being limited to mass-produced plastic figurines and simple geometry shapes when 3D printing. A revolutionary form of 3D printing called selective laser sintering (SLS) has enabled the creation of intricate, durable, and functional parts with industrial-grade materials.
SLS printing brings products straight from a 3D design file to a physical object using an astounding process: a laser selectively fuses powdered material, layer by layer, until the complete form emerges. This technology unlocks new possibilities for rapid prototyping and production across sectors like aerospace, automotive, medical, and consumer products.
With SLS, the time from concept to finished product shrinks substantially. Even small businesses and startups can innovate faster. But diving into printing with selective laser sintering requires an understanding of the technology, materials, applications, and more.
In this in-depth guide, we’ll explore how SLS 3D printing works, its advantages over other methods, key applications, and what this promising technology has in store for the future of manufacturing. Let’s get started!
How Do Selective Laser Sintering 3D Printers Work?
Selective laser sintering (SLS) 3D printers produce objects by using a laser to fuse small particles of plastic, metal, ceramic or glass powders into a mass that has the desired three dimensional shape. SLS allows fabrication of parts with incredibly complex geometry – underhangs, internal channels and optimized topology that might not be possible with any other method.
The SLS printing process consists of the following main steps:
- A thin layer of heat-fusible powder is spread evenly onto a build platform with a roller or blade.
- A laser beam is traced over the powder bed, heating up and fusing together the powder particles in areas corresponding to the cross-section of the object.
- The build platform lowers by the depth of one layer.
- A new layer of powder is spread over the surface and the process repeats, with the laser fusing material in each successive layer.
This happens repeatedly until the full object is formed in the powder bed. Parts are fully encapsulated in unfused powder during printing, so they require no support structures even with complex geometries.
Powder Bed
The powder bed sits in a chamber heated to just below the melting point of the material. This allows the laser to selectively melt the powder precisely where needed. Maintaining the proper temperature ensures uniform melting and even dissipation of heat.
Laser and Scanning System
- The laser is generally a carbon dioxide laser with power ranging from 50 to 500 watts, strong enough to fuse the particles.
- Galvanometer-driven mirrors precisely guide the laser over the powder surface to trace out the pattern for each layer.
- The laser may scan the entire surface or selectively fuse the areas needed for the particular layer.
Materials
SLS can print various materials with high melting points:
- Thermoplastic polymers like nylon, polystyrene and polycarbonate
- Metals including stainless steel, alloy steel, titanium, aluminum and cobalt chromium
- Ceramics such as glass, silica and alumina
The specific powder properties like particle size and melt flow index are tailored for the SLS process.
Post-Processing
Depending on the material, printed parts may require:
- Removal of excess powder
- Infiltration with resin to seal surfaces
- Annealing for stress relief
This improves final part properties.
With its ability to merge powders into robust 3D objects layer by layer, SLS technology enables direct manufacturing of highly complex and durable parts across industries.
Applications of Selective Laser Sintering 3D Printing
Selective laser sintering (SLS) technology has a diverse range of applications across various industries thanks to its ability to produce accurate and durable parts from high performance materials.
Prototyping
SLS is ideal for creating prototypes directly from 3D CAD data. It allows rapid iteration of designs by fabricating multiple versions for testing and evaluation. Parts made from materials like nylon approximate the properties of finished plastic components.
End-Use Parts
The high resolution, detailed features and excellent material properties of SLS printed parts make them suitable for end-use products. Aerospace, automotive and medical companies use SLS to directly manufacture components for final products.
Aerospace
SLS can print aircraft and rocket components in heat and flame resistant high performance materials. It enables consolidation of parts for lighter designs.
Automotive
Auto manufacturers use SLS for customized jigs, fixtures, assembly tools and end-use parts like air ducts. The process suits rapid tooling needs.
Medical Industry
SLS produces customized orthodontic devices, implants, surgical tools and bio-models for surgery planning from biocompatible materials.
Consumer Goods
Retail products like jewelry, footwear, consumer electronics and furnishings printed with SLS offer customized and organic designs.
Rapid manufacturing capabilities, exceptional mechanical properties and accuracy make SLS the choice for diverse applications across many verticals. Parts printed directly with selective laser sintering are already replacing traditionally manufactured objects in many situations.
Advantages and Disadvantages of Selective Laser Sintering
Selective laser sintering (SLS) has unique strengths and limitations compared to other 3D printing processes. Understanding the pros and cons of SLS helps determine when it is the most suitable choice for manufacturing applications.
Advantages of SLS Printing
- High geometric complexity – SLS can fabricate intricate internal features and complex or delicate shapes that are impossible with traditional methods.
- No structural supports needed – The surrounding powder bed provides full support, enabling undercuts and overhangs.
- Mechanical properties – Parts printed in materials like nylon have isotropic properties and behave like injection molded plastics.
- Material versatility – SLS accommodates various powders including plastics, metals, ceramics and glass. Even composite materials are possible.
- Minimal waste – Unfused powder is reused for additional prints, resulting in near zero waste.
Disadvantages of SLS Printing
- Rough surfaces – The layered powder texture creates a gritty surface that needs finishing for aesthetic parts.
- Smaller build volumes – SLS machines typically have build sizes under 1 cubic foot, limiting part dimensions.
- Limited materials – Only certain powders can be selectively sintered, restricting material options.
- High equipment costs – Industrial SLS printers have high price tags of $100,000 to $1 million.
- Slow speeds – Printing happens slower than other processes due to laser scanning time.
The advantages of SLS make it ideal for functional prototypes and end-use parts that benefit from design freedom, strength and complex geometries. The limitations may be outweighed for applications where no other process can construct the required shapes.
SLS vs. Other 3D Printing Processes
Selective laser sintering (SLS) has distinct differences compared to other common 3D printing technologies like fused deposition modeling (FDM), PolyJet, and stereolithography (SLA). Understanding where SLS excels and falls short against other methods helps select the optimal process for an application.
SLS vs. FDM
Fused deposition modeling uses a heated nozzle to extrude thermoplastic filament layer by layer.
- SLS prints higher performance thermoplastic materials like nylon, which have better mechanical properties than FDM thermoplastics like PLA and ABS.
- SLS produces smooth surface finishes, while FDM layers leave visible ridges.
- SLS enables complex shapes without support structures. FDM requires supports for overhangs.
- SLS offers greater accuracy and smaller layer thickness than FDM.
SLS vs. PolyJet
PolyJet 3D printing uses inkjet heads to jet ultra-thin layers of curable photopolymer resin.
- SLS can print production-grade thermoplastics and metals, while PolyJet is limited to photopolymers.
- SLS produces highly durable parts. PolyJet parts are less thermally and mechanically resilient.
- PolyJet offers very high detail resolution. SLS resolution is more limited.
- PolyJet benefits from multicolor printing. SLS can only print uniform colors.
SLS vs. SLA
Stereolithography (SLA) uses a laser to selectively cure liquid resin layer by layer.
- SLS accommodates high performance thermoplastics and metals. SLA uses photopolymer resins with lower strength.
- SLS does not require support structures. SLA needs supports for overhangs.
- SLS produces opaque parts. SLA can produce optically clear parts.
- SLS has slower build speeds than SLA.
Understanding the tradeoffs helps identify when SLS is the optimal 3D printing process for an application needing its unique advantages.
How to Select an SLS 3D Printer
With selective laser sintering (SLS) now viable for mainstream manufacturing, an increasing selection of SLS 3D printers are available. Consider these key factors when choosing an SLS system for your application:
Build Volume
SLS printers range from 5.1” x 5.1” x 4.9” build volumes to 20” x 24” x 18” or larger. Determine the size of parts you will print to narrow down system choices. Larger build volumes offer more design freedom.
Laser Power
Laser wattage affects the precision, speed and types of materials a printer can sinter. Lasers range from 30W to 500W. More power expands material capabilities but increases cost.
Supported Materials
SLS printers generally work with either plastics like nylon, polyamide and PEEK or metals like stainless steel and titanium. Select a system that can process your required material.
Precision
Precision relates to the minimum wall thickness, layer thickness and smallest resolvable feature details possible. SLS can produce layers around 100 microns thick with high accuracy.
Manufacturer
Leading SLS companies include EOS, 3D Systems, Formlabs, Farsoon and Sinterit. Compare quality, performance and cost between manufacturer offerings.
Price Considerations
Industrial SLS systems run from $100,000 to over $1 million. Economies of scale make SLS suitable for larger production volumes to distribute costs.
Operating Costs
Factor in material costs per part. Nylon powder can run $50-$100/lb. Metals like stainless steel can cost $25-$100/lb. Consider un-sintered powder reuse to reduce material costs.
Choosing the right SLS 3D printer requires balancing build parameters, materials requirements, part quality and budget for an ideal solution.
Design Guidelines for Optimal SLS 3D Printing
To achieve success with selective laser sintering (SLS) 3D printing, designs should follow guidelines specific to the SLS process. Following best practices for orienting, supporting and detailing parts helps avoid issues and optimize results.
Wall Thicknesses
Minimum wall thickness depends on material, but a general rule is 0.030 in (0.75mm) for plastics and 0.015 in (0.4mm) for metals. Thinner walls risk warping or breaking.
Spacing/Gaps
Design spacing of at least 0.010 in (0.25mm) between walls or detailed features. This prevents fusing together in the powder bed.
Surface Finishes
SLS produces a gritty powder texture. Include 0.002-0.012 in (0.05-0.3mm) of stock material if a smooth surface finish is needed.
Part Orientation
Orient the part to minimize support structures. Tilting flat surfaces 15-45° from the horizontal plane enables “stairs stepping” to avoid supports.
Supports
While SLS does not require dedicated support structures, some overhanging geometries may benefit from thin auxiliary supports to prevent distortions.
Software
Use robust 3D modeling software that accounts for shrinkage and design principles suited to powder-based printing.
Following SLS design guidelines helps identify and prevent common issues like warped geometries, adhered components, and poor surface finish for superior printed results.
The Future of Selective Laser Sintering 3D Printing
Selective laser sintering (SLS) is already an established 3D printing process, but constant advances are expanding the technology’s capabilities and applications even further.
Emerging Applications
SLS can produce detailed lattices and foams impossible with other methods. It is being used for customized foams and structures for orthotics and sporting equipment.
New Materials
Research is developing SLS printing with new materials like composites by sintering coated particles. This could enable functionally graded objects.
Hybrid Multi-Material
Hybrid SLS printers with multiple powder beds and lasers can print parts using two or more materials like plastics and metals.
Improvements in Speed
A wider scanning laser combined with faster motors and processing allows SLS printing at higher speeds closer to injection molding.
Larger Build Volumes
Larger format SLS printers are being developed to accommodate bigger parts required by industries like aerospace and automotive manufacturing.
Advances in Quality
Algorithms that adapt laser parameters during printing mitigate distortions and stresses for higher accuracy and material properties.
Desktop SLS
Smaller, lower cost SLS printers make the technology more accessible. However material options are still limited compared to industrial systems.
SLS is already an innovative manufacturing process and will only become more versatile and feasible for end-use parts production as it continues advancing.
The Power of Selective Laser Sintering 3D Printing
Selective laser sintering is spearheading the next generation of manufacturing. By using a laser to fuse powders into 3D objects layer-by-layer, SLS can create highly complex geometries and advanced end-use parts direct from digital files.
SLS unlocks new design freedom thanks to its ability to produce intricate details, undercuts, hollow internal channels and delicate structures that are impossible with traditional methods. It accomplishes this without needing dedicated support structures.
The technology can print an expanding array of high performance materials like nylons, metals, ceramics and composites with properties matching or exceeding those from conventional manufacturing processes. No longer restricted to prototyping, SLS enables direct digital production of finished components across aerospace, automotive, medical and consumer industries.
While SLS does have limitations like smaller build volumes and high machine costs compared to other 3D printing processes, the unique capabilities it provides make SLS the ideal choice for countless applications. As the technology progresses, SLS will only become faster and more versatile.
Selective laser sintering represents an innovative leap into the future of manufacturing. It makes rapid product development and agile production a reality. SLS expands the design possibilities for engineers and designers, unleashing new potential for optimization and innovation across industries. Parts formed layer-by-layer directly from digital files are the new frontier of manufacturing.