Selective laser sintering (Selective laser sintering -/SLS/) is the leading 3D printing technology for durable fixtures, lightweight components and fast, functional replacement parts, but how does it work and which SLS 3D printers do it best?
Advances in technology have made SLS 3D printers more affordable and compact. Not long ago, all SLS machines were bulky and expensive, but now there are a number of office-friendly desktop SLS 3D printers on the market. Even industrial machinery today has become cheaper and easier to use than traditional manufacturing methods such as injection molding and CNC milling.
Given today's supply chain disruption and rising manufacturing and transportation costs, SLS 3D printing is an alternative that allows businesses to introduce prototypes, spare parts and manufacturing for internal use and needs.
Valued for its ability to create engineering-quality parts with excellent mechanical properties and fine resolution quickly, SLS 3D printing is what engineers and industrial designers turn to for functional rapid prototyping and higher volume end-use parts. If you're not familiar with the technology, in a nutshell, it uses lasers to fuse powdered plastic material together into 3D shapes layer by layer. This is a category of “powder bed fusion” 3D printing. (We go deeper into the details below.)
The technology is popular for functional prototypes, replacement parts, fixtures, design evaluation models, small to medium production runs, and consumer end-use products.
Industries that have embraced the glow of SLS include:
- Cars (gadgets, prototype cars, racing car parts)
- Aerospace (prototypes, instruments, ducts)
- Medicine and healthcare (prosthetics, braces)
- Consumer electronics (cases, prototypes)
- Military (spare parts, grips)
- Heavy industry (sand casting models, tools)
SLS 3D printing is widely used today because it rivals injection molding products in terms of strength and precision. Compared to injection molding, 3D printing can create parts that injection molding can't, such as things that have internal channels, lattice structures, and other geometrically complex elements.
How does an SLS printer work?
SLS is a powder layer fusion technique that uses a laser to selectively sinter (not melt) polymer powder particles, fusing them together with heat and pressure layer by layer until a 3D design is produced. An SLS printer can have one or many lasers of different types (fiber, diode laser, CO2, etc.) and powers (10 watts, 60 watts, 100 watts).
The process begins by heating the powder container filled with powdered material to just below the melting temperature of the polymer. A recoating blade spreads a thin layer of powder over the build platform. A laser (or lasers) then scan the contour of the layer and sinter the powder particles. To ensure that the part is fully intact, the entire cross-section of the desired component is scanned. Once the layer is complete, the build platform moves down and the blade re-coats the surface with a clean powder. This process is repeated until the part or parts are completed.
Once the printing process is complete, there is quite a bit of post-processing. Once the build chamber has cooled, which can take hours, you'll find that the solid 3D printed part is encased inside the unsintered bulk powder bed. To "dig" your parts, you'll take the build camera to a dedusting station. With a brush, air blower, or some other form of blasting technique, you remove the loose dust and collect it for use in the next print. Additional dedusting devices reduce the mess, but they will naturally add to the total cost of your SLS investment.
Unlike some other 3D printing technologies, the residual powder can be reused for the next print job. Depending on the machine you will need to add 10% to 70% fresh powder for the next print.
Advantages of SLS technology
The main reason for choosing SLS technology over 3D printers that use polymer filaments (called FDM printers) is to obtain prints with excellent and consistent mechanical characteristics.
Mechanical properties
The lasers used in SLS fuse the polymer particles into a solid so the layers are virtually invisible. Strength and durability are on par with (or better than) injection molded parts. SLS 3D printing with industrial grade materials such as carbon fiber nylon produces parts strong enough for use in harsh environments.
Design possibilities
Another reason engineers are turning to SLS 3D printing is that it can produce parts with complex designs that are not possible or impractical with conventional manufacturing methods. Designers can consolidate complex assemblies that would normally require multiple parts into a single part. This helps alleviate weak areas and reduces assembly time. Parts can be created with internal lattice structures to reduce weight while maintaining strength.
Fast and productive
SLS printing is typically a rapid additive manufacturing technology for functional, durable prototypes and end-use parts, but the speed depends on the printer. An industrial 12-laser SLS printer will print faster than a single-laser machine for example. That being said, SLS is faster than the layer deposition methods used in FDM.
Also, you are not limited to print part by part. You can actually fill your build chamber to the brim with parts, which is especially useful for printing multiple iterations at once.
Affordable
Especially for low-volume replacement parts, prototypes, and custom tooling on a part-by-part basis, SLS 3D printing is less expensive than traditional manufacturing methods because no tooling or molds are required.
SLS 3D printing is usually the more affordable solution even after purchasing the machine and materials if your business needs small-run products, prototypes, and unique parts.
SLS materials
Can all SLS printers print with all SLS materials? Unfortunately- no. Some SLS printers can only print with the two most common materials (PA 12 and PA 11), while others can print with many more. Some printers have lasers that are not powerful enough for certain materials, while many manufacturers offer materials that are customized to work best on their printers.
Always check with your printer manufacturer which materials are approved for use, as although some materials may work in general, your print may not show the promised strength or flexibility unless printed on an approved machine.
An open material system SLS printer can produce quality parts from a wide range of materials supplied by an equally wide range of manufacturers, so you have some choice when shopping. A closed system SLS machine is approved for use only with materials recommended by one manufacturer (usually the printer manufacturer). Typically, SLS prints have a matte, rough surface that can be smoothed out with post-processing.
Below is an overview of the most popular SLS 3D printing materials in use today (although there are others).
The most popular SLS powder materials:
- PA 12 (Nylon)
- PA 11 (Nylon)
- TPU (Nylon)
- PA 12 CF (Carbon Fiber-Filled Nylon)
- PA 12 – GF (Glass-Filled Nylon)
- Alumide (Aluminum-Filled Nylon)
- Biomedical
- PEEK
- PEKK
- PP
SLS printer and workflow software
You can use any CAD software (Fusion 360, SolidWorks, Onshape, etc.) to design your part or product. Once you have a design, you'll export it to a 3D printing file format, such as STL, OBJ, or 3MF, and upload it to your SLS printer software. Each SLS printer is controlled by proprietary software to turn your digital part file into code that your printer can follow to produce your part.
Unlike the sea of free and generic software options for FDM machines, SLS 3D printers usually come with their own software, making it an important part of your consideration when buying a printer, as some have unique features.
The SLS printer software is where you set a set of print settings, orient and line up parts in the build camera, and slice the digital model into individual layers for printing. More advanced SLS machines usually have more advanced software features that allow you to fine-tune various settings to get the exact results. Many also have preset print profiles that automate the entire process.
After the setup is complete, the print preparation software sends the instructions to the printer via a wireless or wired connection. The software will give you an estimated print time. If you use more than one SLS printer, some software solutions will provide information about all your print jobs from a single dashboard, from print preparation to job status and printer performance in real time.
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