How Does Sls Work
Here is how the SLS fabrication process works:
I. The powder bin and the build area are first heated just below the melting temperature of the polymer and a recoating blade spreads a thin layer of powder over the build platform.
II. A CO2 laser then scans the contour of the next layer and selectively sinters the particles of the polymer powder. The entire cross section of the component is scanned, so the part is built solid.
III. When the layer is complete, the build platform moves downwards and the blade re-coats the surface. The process then repeats until the whole part is complete.
After printing, the parts are fully encapsulated in the unsintered powder and the powder bin has to cool down before the parts can be unpacked. This can take a considerable amount of time . The parts are then cleaned with compressed air or other blasting media and are ready to use or further post process. The remaining unsintered powder is collected and can be reused .
How Does Sls Printing Work
Today, there is a whole group of 3D printing technologies which use powdered materials to create physical objects by heating the material. The key to understanding the specifications of SLS among other similar methods is behind these three words:
Selective printer receives a code for each layer of the object, which tells it where the material should be selectively solidified to get a 3D structure.
Laser a high-powered laser to heat powder grains and make them solidify together to form an object, layer by layer.
Sintering the powder isnt just heated, its sintered to the point at which grains solidify. Its important to note that since the printer doesnt completely melt the material the parts come out porous.
With no magic involved, SLS printers work through a very simple process. To start printing, the machine requires only two things a file with a code and material used to produce the parts.
- The machine preheats the whole build chamber with powder to the temperature just a little below the sintering point
- Roller creates a thin flat layer of powder across the platform
- Laser sinters zones, where object is supposed to be according to the code
- Platform descends slightly
- Printer repeats the key three steps again and again until the last layer required has been completed
- The powder needs to cool down before it can be removed from the machine.
Fuse : The First Benchtop Industrial Sls 3d Printer
Just like with other 3D printing technologies like FDM or SLA, lower cost, compact SLS systems have recently started to emerge on the market, but these solutions came with considerable trade-offs. These include lower part quality and complex, manual workflows resulting from the lack of post-processing solutions, which have so far limited their use in industrial and production settings.
The Formlabs Fuse 1 aims to bridge this gap and create its own category with the first benchtop industrial SLS 3D printer that offers high quality, compact footprint, and a complete, simplified workflow at a fraction of the cost of traditional industrial SLS systems.
The Fuse 1 requires no specialized infrastructure, and can easily fit into your workspace.
The Fuse 1 uses a single laser and has a smaller build chamber that requires less heating. As the powder gets exposed to elevated temperatures for a shorter period of time, there is no need for inert gases and specialized air handling equipment. The lower energy consumption means that it can run on standard AC power without requiring specialized infrastructure.
The Fuse 1 features a patent-pending solution called Surface Armor, a semi-sintered shell that keeps the area around the parts evenly heated as they print, ensuring great surface finish, consistent mechanical properties, high reliability, and high refresh rates.
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History Of Selective Laser Sintering
Selective Laser Sintering was developed by the now Dr. Carl R. Deckard whilst he was still an undergraduate at the University of Texas. The development was with his professor at the time, Joe Beaman. After developing the process, Dr. Deckard went on to start up Desk Top Manufacturing which was later sold to 3D printing giant 3D Systems in 2001 for a reported $45 million.
Selective laser sintering was only an industrial method until the patents expired, and almost all SLS printers were industrial machines costing over $250,000. However, now with patents expiring new companies have created lower cost alternatives, such as the Sinterit Lisa, or Sintratec printers. SLS is commonly used for rapid prototyping offered by a wide variety of 3D printing services.
Best Suited Sls Printing Materials
The most commonly used material for SLS printing is Polyamide 12, aka Nylon 12. Polyamide 12 is ideal for intricate joints and assemblies and durable components. Other compatible materials are PEEK and PA 11, but their overall usage is very low.
Several additives such as glass fibers and carbon fibers are blended with polyamide powder to enhance the mechanical and thermal properties of the sintered component. However, parts made with blended materials might become more brittle in nature.
Heres a table describing the benefits and limitations of potential materials:
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Materials For Sls 3d Printers And Outlook
But one can come up with a question of materials available for SLS. The variety is broad from different metal powders utilised mostly in the automotive industry to polyamides and thermoplastic polyurethane such as Flexa Grey. All powders can be altered for specific application so everyone can achieve desired mechanical properties of the model.
SLS is actually a zero waste technology where the unsintered powder can be used for next prints over and over again. A vital aspect is the way of reutilising the used powder and its refresh ratio . In theory one can use the same powder all over with the fraction of the new one. However, some of the powders can oxidize quickly and require the presence of neutral gas atmosphere such as nitrogen to preserve the print quality. This type of solution is present in Sinterits Lisa PRO which has a nitrogen intake.
Printouts from different kinds of materials:
If this article made you hungry for knowledge, check out the next part: Selective Laser Sintering in Details
History Of Sls 3d Printing
I deliberately decided to talk about SLS history at the end it was invented in the 1980s by Dr. Carl Deckard and Dr. Joe Beaman at the University of Texas at Austin. The initial prototype is evolved drastically and developed to work with a wide array of materials such as plastics, metals, ceramics, glass, and various composites and blends.
Collectively the method of processing all the above materials is called the bed fusion method. There are two main bed fusion methods- SLS and DMLS .
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Prone To Shrinkage And Warping
Much like SLA and FDM, SLS prints are also prone to warping and shrinkage. The nylon powder needs to be subjected to elevated temperatures to enable sintering, which means that the printed object will undergo a cooling process almost immediately after the solid layer has formed. As the print cools, it contracts or shrinks in all directions which can lead to a dimensionally inaccurate product. The stress due to the contraction can also accumulate in certain parts of the print, particularly in sharp edges and corners, resulting in these parts getting warped or distorted.
Unlike in FDM printing, there is no intervention or modification of the SLS printing process that can be done to reduce warping. Shrinkage will inevitably happen at a rate between 3% to 4%. This needs to be considered in the design phase by adjusting the volume of the model accordingly.
Warping can be reduced by avoiding or reducing the volume of flat areas in the design. Cutouts can also be integrated into the design that can absorb some of the stress caused by absorption without distorting the rest of the print.
Key Attributes Of Sls
The machine manufacturer plays a key role in deciding the process criteria of SLS. If a manufacturers focus is on small-scale productions, then it becomes extremely important to take the necessary advantage of the build volume. Although the defined layer height 100-120 microns, a random height bin will take about the same time to print regardless of the number of parts it accommodates.
The reason behind that is the processing time is decided by the re-coating steps, and the machine will cycle through the same number of layers.
The additional benefit of SLS compared to other 3D printing methods is its fantastic bond strength between layers, leading to printed parts with phenomenal mechanical properties.
SLS parts also boast good tensile strength and modulus but have a weak elongation at break. Thats because of the internal foraminous of the last part.
Warping is SLS parts are uncommon but not completely absent either. It happens when the newly sintered layer cools, its dimensions contract, and internal strain builds up, pushing the central layer upside.
Flat surfaces are often more susceptible to warping, but manufacturers with a good presence of mind adjust the design and size accordingly. The prime causes can differ, but adjusting the part vertically in the build platform should be avoided.
The typical shrinkage in SLS parts is 3-3.5%
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When To Use Sls Vs Slm
Because additive manufacturing works by building up layers instead of removing material, SLS, SLM and other 3D printing technologies are most useful for products with complex internal geometries like spiral vents and nested cores, or for rare metals that would be prohibitively expensive to machine. 3D printed metal can also be an effective option for manufacturing very small batches of metal parts or for projects with very short timelines.
In other cases, 3D printing metal is often substantially more expensive than CNC machining, especially for medium- to large-sized productions. Though it has longer lead times, machining is still quite cost-effective for small batches and becomes substantially less expensive at medium to high volumes. Moreover, metal machining yields superior fine detail and surface finish when compared to printed metal.
At the same time, other modern 3D plastic printing technologies like the HP Multi Jet Fusion 3D printer, are extremely cost effective for small- to medium-sized productions. The Multi Jet Fusion is able to print industrial-strength parts at a fraction of the cost of SLS and SLM. Its quicker, too MJF printing is many times faster than any other 3D printing technology, machining or injection molding. Depending on the demands of your project, plastic printing may even be a viable alternative to metal printing.
No Need For Support Structures
One of the chief benefits of using SLS printing is that it designs do not need any support structure. As the print is being built, all hollow spaces are automatically filled with unused powder, thus making SLS prints self-supporting. This offers modelers and product designers a huge degree of design freedom. Models with large hollow spaces, overhanging features, and very thin features will no longer be a problem when printing with SLS. Printing with SLS can also be a viable solution for printing complex designs that would otherwise require printing in multiple parts with FDM or SLA.
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Sla Printing: Basics And Benefits
Inverted stereolithography, also known as upside-down, is the most common and well-known version of SLA printing.
The necessary steps during the inverted SLA process are as follows:
What remains is a finished product that is smooth but covered in support structures.
SLA 3D printers use CAD drawings that you load into your printer via USB. Once you upload the design, the rendering will show the support structures that need to be present for the design not to wilt under its weight. Some machines allow you to shift the frames manually.
What Is Sls Printing
SLS printing is one of the most popular and widely used 3D printing methods. It belongs to the powder bed fusion group. Selective laser sintering means a laser carefully sintering the particles of a material powder, combining them, and building the part layer by layer.
The materials which are used for SLS are thermoplastics used in granules form. SLS is considered a competent method to produce parts within a stringent deadline. It is compatible with low-volume production-grade manufacturing. The layer-by-layer manufacturing technique can produce parts with intricated geometries with less time and title to no waste.
Apart from speed, consistency, and the capability of producing parts with great mechanical properties makes SLS stands out among other 3D printing methods such as SLA and FDM. However, for utilizing all the capabilities offered by selective laser sintering, one must have an elaborate knowledge of its benefits and limitations.
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A Brief History Of Sls 3d Printing
Selective laser sintering was one of the first additive manufacturing techniques, developed in the mid-1980s by Dr. Carl Deckard and Dr. Joe Beaman at the University of Texas at Austin. Their method has since been adapted to work with a range of materials, including plastics, metals, glass, ceramics, and various composite material powders. Today, these technologies are collectively categorized as powder bed fusionadditive manufacturing processes by which thermal energy selectively fuses regions of a powder bed.
The two most common powder bed fusion systems today are plastic-based, commonly referred to as SLS, and metal-based, known as direct metal laser sintering or selective laser melting . Until recently, both plastic and metal powder bed fusion systems have been prohibitively expensive and complex, limiting their use to small quantities of high value or custom parts, such as aerospace components or medical devices.
Innovation in the field has surged recently, and plastic-based SLS is now poised to follow other 3D printing technologies like stereolithography and fused deposition modeling to gain widespread adoption with accessible, compact systems.
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.
Understanding how SLS additive materials work for your business
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Types Of Sls Printed Materials
- Metal: Aluminum, steel, titanium and a variety of alloy particles are used to create objects with the proper strength properties.
- Polymers: Nylon and polystyrene are two polymers popularly used in SLS. The material can be glass-filled or be impact resistant, depending on the exact formulation of the material.
- Glass: This material is used in design, art and by hobbyists.
- Rubber-like materials: These flexible materials are typically proprietary, such as Duraform Flex plastic from 3D Systems.
- Green sand: A mix of silica sand, chromite sand, bentonite/clay, water, anthracite and inert sludge is known as green clay. The name refers to the fact that it is used to make molds for castings while the material is still “wet” and therefore “green” as opposed to dry/cured.
Similarities In Sls Vs Sla 3d Printers
The only similarity in the technology of SLS printing and SLA printing is the use of a laser to shape the material. This may seem like a surface-level similarity, but it does lend itself to some common characteristics.
For example, designs printed by SLS printers and SLA printers are very precise. Both SLS and SLA printers are much more precise than FDM printers. Also, the use of a laser to shape the object means that hot ends are not necessary. Hot ends can cause a lot of problems in 3D printing.
They can jam or become clogged. The use of lasers in both SLA and SLS printing also eliminates the risk of prints becoming warped, which is always a risk when using an FDM printer.
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Appearance & Surface Quality
The fusing agent currently used in MJF systems is black in color because dark materials absorb radiation more effectively. As a result, MJF parts have a light grey appearance. An optional post-processing dyeing step can be applied to achieve an uniform black finish.
SLS parts are usually printed white and can be dyed to any color. Grey SLS nylon powder is also available and parts printed in this material have a very similar look to MJF parts but are smoother to the touch.
Parts printed in both technologies have a grainy surface finish, but can be post-processed to a very high standard. If aesthetic appeal is the main requirement, dying is highly recommended.
Sintratec Kit Diy Sls 3d Printer
- Cost: 4,999
- Company based: Switzerland
- Print volume: 110 x 110 x 110 mm
The Sintratec Kit is the only DIY 3D printer kit on this list, and is currently the only DIY SLS 3D printer for sale in the world! Creating an SLS 3D printer kit is a huge achievement considering how much more complex SLS is compared to fused deposition modeling, though the Sintratec takes far longer than a standard kit printer to assemble.
After successfully crowdfunding this SLS 3D printer back in 2014 raising $213,337, more than their original $175K goal the Sintratec DIY SLS printer kit has since been released worldwide.
With a modest 110 x 110 x 110 mm print volume, medium-sized parts can be printed without issue. For printing many parts simultaneously however, this may not be the machine for you. The Kit takes around 4 days to assemble, though Sintratec say no specialist technical knowledge is required. You can easily connect to the printer via USB to print, and Sintratec sell their own plastic powders.
If you want to try Selective Laser Sintering and dont want to break the bank, the Sintratec Kit is also the cheapest SLS 3D printer out there, at just 4,999 if you dont mind building it yourself.
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