What is Selective Laser Sintering 3D Printing?
Selective laser sintering is an additive manufacturing (AM) technology that uses a high-power laser to sinter small particles of polymer powder into a solid structure based on a 3D model.
SLS 3D printing has been a popular choice for engineers and manufacturers for decades. Low cost per part, high productivity, and established materials makes the technology ideal for a range of applications from rapid prototyping to small-batch, bridge, or custom manufacturing.
Recent advances in machinery, materials, and software have made SLS printing accessible to a wider range of businesses, enabling more and more companies to use these tools that were previously limited to a few high-tech industries.
How SLS 3D Printing Works
As a self-supported additive manufacturing process, SLS has capabilities and precision other processes lack.
While other 3D printing processes require either support materials or 3D printed supports to be added to the design, SLS allows parts to be printed as-is. This unique capability saves time and reduces the skill needed to prepare a print for an SLS machine.
The SLS 3D printing process is broken into three distinct steps:
- Printing,
- Cooling, And
- Post-Processing.
Printing
The SLS printing process is unique when compared to other additive manufacturing processes like fused deposition modeling (FDM).
First, the raw powder is preheated (so the laser requires less energy) and deposited in a thin layer on top of a platform in the build chamber.
The laser then scans or shoots the slice of the powder in the shape of the model for that cross-section, sintering material as it goes.
The remaining unfused powder acts as a support layer as the build chamber lowers by one layer and more material is added. The process repeats itself until the build is complete.
Cooling
The finished printed part is then suspended within a bed of hot powder. To reduce defects and increase dimensional stability, the build chamber must cool down evenly, which can take up to half of the total build time.
This cooling should be gradual, and cooling of the build chamber reduces mechanical defects and helps reduce warping.
Post-processing
Once cool, the excess powder is removed and recycled. To recover parts from the build chamber, the parts are sifted manually to remove excess powder, then cleaned with compressed air to prepare them for final processing.
SLS parts are known for the unique surface finish caused by the sintering process. For exceptional material properties and finish quality the part may be post-processed sandblasting and media tumbling are used to improve the surface finish.
Selective Laser Sintering (SLS) Materials
The most common material for selective laser sintering is nylon, a highly capable engineering thermoplastic for both functional prototyping and end-use production. Nylon is ideal for complex assemblies and durable parts with high environmental stability.
SLS 3D printed nylon parts are strong, stiff, sturdy, and durable. The final parts are impact-resistant and can endure repeated wear and tear. Nylon is resistant to UV, light, heat, moisture, solvents, temperature, and water.
3D printed nylon parts can also be biocompatible and not sensitizing, which means that they are ready to wear and safe to use in many contexts.
Nylon is a synthetic thermoplastic polymer that belongs to the family of polyamides. It is available in multiple variants, each tailored to different applications.
Nylon 12 and nylon 11 are the most common single-component powders, and both can also be reinforced with other materials like glass or carbon fiber to create composites with specific properties, like added strength and rigidity.
Besides nylon, polypropylene (PP) is another popular SLS 3D printing material. PP is ideal for producing fully functional, lightweight parts that offer the mechanical properties of common injection molded polypropylenes, ensuring durability in demanding environments for prototypes or end-use applications.
SLS 3D printers can also create flexible TPU parts with unmatched design freedom and ease. Combining the high tear strength and elongation at break of rubber materials with the versatility of SLS 3D printing, TPU is ideal for producing flexible, skin-safe prototypes and end-use parts that withstand the demands of everyday use.
The specific material selection is dependent on the printer model. The following materials are compatible with the Fuse 1+ 30W:
Nylon 12 Powder
General purpose, versatile material with high detail and great dimensional accuracy.
- High performance prototyping
- Small batch manufacturing
- Permanent jigs, fixtures, and tooling
- General SLS parts
Nylon 11 Powder
Ductile, strong, flexible material for when durability and performance are key.
- Impact-resistant prototypes, jigs, and fixtures
- Thin-walled ducts and enclosures
- Snaps, clips, and hinges
- Orthotics and prosthetics
Nylon 12 GF Powder
A glass-filled material with enhanced stiffness and thermal stability for demanding industrial environments.
- Robust jigs and fixtures and replacement parts
- Parts undergoing sustained loading
- Threads and sockets
- Parts subjected to high temperature
Nylon 11 CF Powder
Get the best of nylon and carbon fiber with this highly stable, lightweight, high-performance material.
- Replacement and spare alternatives to metal parts
- Tooling, jigs, fixtures
- High-impact equipment
- Functional composite prototypes
Polypropylene Powder
Genuine polypropylene for works-like prototypes and durable end-use parts that are chemically resistant, weldable, and watertight.
- Watertight housings, cases, packaging prototypes
- Orthotics and prosthetics
- Automotive interior components
- Strong and chemically resistant fixtures, tools, and jigs
TPU 90A Powder
An elastomer with high elongation at break and superior tear strength for flexible, skin-safe prototypes and end-use parts.
- Wearables and soft-touch elements
- Padding, dampers, cushions, and grippers
- Gaskets, seals, masks, belts, plugs, and tubes
- Soles, splints, orthotics, and prosthetics
Selective Laser Sintering (SLS) Applications
SLS uses production-grade nylon materials, resulting in durable, functional parts that last, rivaling parts produced using traditional manufacturing methods.
The robustness of SLS makes this technology great for:
General
- Functional Proof of Concept Models
- Design Evaluation Models (Form & Fit)
- Engineering Design Verification
- Product Performance and Testing
- Wind-Tunnel Test Models
Rapid Manufacturing
- Aerospace hardware
- Medical and healthcare
- Electronics; packaging, connectors
- Homeland security
- Military hardware
Tooling and Patterns
- Jigs, fixtures and tools
- Investment Casting Patterns
Production
- Short run end-use components
- Complex plastic parts
- Part consolidation exercises
Why Use Selective Laser Sintering?
SLS is used in a variety of end-use applications in industries including automotive and aerospace.
Considering its robustness and capability to produce highly complex parts, SLS can introduce major time and cost savings for small-run parts that would otherwise require assembly with traditional manufacturing. SLS is a perfect marriage of functionality, strength, and complexity.
#1. Robust, Performance Parts.
SLS technology produces tough and durable parts that excel in high-performance prototyping and end-use applications. 3D Systems SLS materials have been optimized, validated, and tested to ensure quality, with uniform 3D mechanical properties.
#2. High Speed and Throughput.
Large SLS build capacities paired with fast build times, high-density nesting, and no support structures help you maximize every print for more parts, sooner.
#3. Best-In-Class Part Quality.
Side-by-side comparison testing shows 3D Systems SLS printers provide best-in-class part quality. Get superior accuracy, part resolution, edge definition, and surface finish with 3D Systems’ SLS solutions.
#4. Broad SLS Materials Selection.
Manufacture with true nylon materials that answer your application requirements. Whether you need toughness, heat resistance, flame retardancy, flexibility, or food-grade and medical-grade options, the 3D Systems SLS materials portfolio has you covered.
#5. Functional Design.
As a self-supporting build methodology, SLS enables the production of complex geometries, such as monolithic designs, lightweight components, and mass-customized products, that could not be manufactured any other way.
#6. Low Part & Ownership Costs.
The features and capabilities of 3D Systems’ SLS deliver up to 20% lower operational costs compared to similar printers. These include automated production tools, high throughput, material efficiency, and repeatability, just to name a few.
Advantages of Selective Laser Sintering (SLS)
SLS is reliable, precise and one of the fastest ways of producing prototypes and small-volume batches of parts. It has some distinct advantages over other processes:
1. No support structures
Unlike some other 3D printing processes, the part does not need any support structures since empty spaces are filled with unused loose powder making it self-supporting.
This allows you the freedom to design empty hollow spaces, overhanging features and very thin features.
It means you can design parts with complex internal components or channels without the fuss of support structures (be sure to consider design guidelines though, to ensure proper removal of remaining powder).
If you need a complex design, it is a good option and you don’t need to produce multiple parts to achieve this.
2. High productivity
The process is one of the fastest 3D printing technologies since the lasers have a fast-scanning speed and the powders used only need a short exposure for fusing.
In addition, we can tightly arrange multiple parts in the chamber with minimal clearance to maximise the available build space – so you get more parts produced faster.
3. Excellent mechanical properties
The SLS process produces very strong adhesion between layers so parts have good isotropic properties. This means that their tensile strength, hardness and elongation to break are similar across the x, y and z axes.
These properties mean that the printed parts are often a good alternative to injection moulded parts whether for prototyping or to produce low volumes. Because of the materials used, generally Nylon, the parts also offer good chemical resistance.
4. Ideal for dying and colouring
Parts produced by SLS tend to have a porous surface which could be an advantage or a disadvantage depending on your application. What it does mean is that they are an excellent choice for dying or colouring.
5. Reduced product development time
Like all 3D printing technologies selective laser sintering allows engineers to prototype parts cost-effectively early in the design cycle, since it does not require tooling and involves minimal set up.
For low volume production you may even choose to use the same machine to produce end use parts. It means that you can test and alter prototypes quickly over the course of just a few days and move to production rapidly.
Disadvantages of Selective Laser Sintering (SLS)
Like any production technology SLS does have its disadvantages and there are occasions when it may be better to consider alternatives whether that’s another 3D printing process, CNC machining or injection moulding.
You will probably find that some of the disadvantages are not too much of an issue when you dig a bit deeper and others can be overcome through postprocessing.
1. Fewer materials
You don’t get a wide choice of materials for SLS. For example there are range of materials, from flexible TPU and PA 12 Flex to tough PA 12 40% Glass Filled and PA12 Carbon Filled, while having a great general-purpose material, PA 12 White.
We find that most projects use nylon-based materials, or polyamides, which are excellent engineering-grade plastics that can be used across a wide range of applications.
Nylon is also freely available and relatively cost-effective.
2. Rough surface and porosity
The same porosity that makes SLS printed parts so great for colouring, also means that they have a relatively rough surface, are not leakproof and have a low impact strength, or brittleness.
If these factors are important, then it’s worth noting that they can be overcome using a post-processing technique called vapour smoothing.
As the name suggests this process produces a smooth surface, that is leakproof and it even improves mechanical properties such as impact strength and elongation at break.
3. High shrink rate
Because the print powder is subjected to high temperatures for it to sinter, this does mean that as it starts to cool it shrinks which can produce a dimensionally less accurate part than other additive manufacturing technologies. Depending on the design, the shrinkage rate can be as high as 3 to 4%.
It means that you will need to allow for this in your design and adjust the volume of the part accordingly. The stress caused by this contraction can also warp or distort sharp edges and corners.
Read more about the 7 mistakes to avoid when designing 3D printed parts to help avoid such problems.
4. Higher waste than other additive manufacturing
One of the key advantages with additive manufacturing is the minimal waste of material using the technology.
Unfortunately, SLS does produce some waste since the powder in the chamber is preheated so that it will sinter with minimal exposure to the laser.
This can cause particle grains in the loose powder bed to partially fuse which compromises its quality for reuse. In practice while you can recycle some of the unused powder, some will be waste.