SLS printing, or Selective Laser Sintering printing, is a form of 3d printing that uses a laser to melt very fine plastic or metal dust in precise ways. It allows a model, or models, to be created encased in powder.
SLS printing is not affordable for home use. Most systems are over $13,000.00USD and require special additional equipment and safety features to be in place to use. This, effectively, removes SLS printing from consideration for home use.
It may be too expensive for the average hobbyist’s home, a dedicated person could consider it, as could small businesses. Full featured setups, with the extra equipment and post processing machines and tools, could be purchased for under $25,000.00USD, comparable to small business Xerox printers, or Direct-to-Garment printers for paper or garment printing companies. It’s in the same ballpark.
How Does SLS Printing Work?
additive manufacturing (AM) technique that uses a laser as the power source to sinter powdered material
SLS printing, or selective laser sinter printing, is a technology that uses a laser to push already hot powder over the melting point, then allowing it to cool. It is an additive technology, in that the powder is layered on, laser sintered, then the next layer is added on, and so on until the model is complete.
The first layer of powder is deposited into an empty build chamber. A laser draws the pattern for that layer, moving in the X and Y plane, with high precision, to melt the material that’s put down. An entire layer of powder is added at a time, then the laser drawing happens. This means that for every layer, it’s quite possible that most of the layer will remain in powder form.
What this means is that if you were only printing one object, you would likely waste a vast majority of the build volume of the printer. It deposits the powder, layer by layer, even if you’re not sintering that particular area, filling up the entire build chamber.
This, however, can provide you with a bonus. Since the powder is there, filling up the layer, it acts as support material for objects above it. So instead of printing one small object on the bottom of the build chamber, you can (and should) print many (either the same or different) models in the volume, stacking them up in the X, Y and Z space. Parts can be stacked right on top of each other, with a small layer of powder between them. It means that if a model would fit in one corner of the build chamber, you might be able to produce three times on the X axis, 3 times on the Y axis, and 4 times on the Z axis, or 36 models in the same build. That’s quite impressive.
On an FDM filament printer or a DLP resin printer, you could only fill up the X axis and the Y axis with models. You can’t stack them (at least not easily).
Once the printer has completed its print run, the material must cool to the point that everything can be handled. This can take quite a while (multiple hours). You want the newly formed plastic parts to cool so that when you remove them from the remaining powder, they won’t bend and deform. It’s simply a matter of brushing away the remaining powder material to get the parts clear.
At this point, the parts are already usable. You may wish to sandblast the parts to smooth the surface, but that’s up to you. It’s not required, unless you require a smoother or finer finish.
What Do SLS Printers Cost?
The major downside for the SLS printing in the home is cost. These machines can be quite expensive. If you look at the print volumes, you’re not so far off DLP resin printers, and the Elegoo Mars at Amazon.Com will run you $259.99 (or a savings of 97.4% over the Fuse 1 printer alone). That’s mind bogglingly different in price.
- Formlabs Fuse 1 printer: $9,999.00USD. Finishing station and printer together, @19,999.00USD from https://formlabs.com/3d-printers/fuse-1/
165 x 165 x 320mm build volume (6.5″ x 6.5″ x 12.5″)
- SinterIt Lisa setup with printer and sandblaster is $13,910.00USD from https://www.3dherndon.com
150 x 200 x 150mm build volume (5.9″ x 7.9″ x 5.9″)
What Materials Can You 3d SLS Print With?
Fuse 1 and Lisa both can print with nylon or polyamide powders. They can’t handle metals or other powdered material. For mechanical parts, nylon is an excellent material with good definition and handles friction well. One example Formlabs uses is a bicycle pedal printed on the Fuse 1 that a staffer has used for multiple years as a replacement part on his bicycle.
The Downsides To 3d SLS Printing?
Cost, cost and cost are the biggest downsides to 3d SLS printing. But cost is not the only downside. The material is a very fine powder that gets everywhere. You’ll have to use breathing filters, and it gets everywhere. Plus, when you first take the powder out from the printer, it’s hot. Really hot. This can be a major health risk, and should be treated with extreme caution. Both companies listed above do have ample training and safety protocols for you to follow, but it remains risky, if not downright dangerous.
Due to the heating of the powder to a specific temperature, and the cooling down after the printing, time is also a downside. It can take over an hour to bring the powder up to temperature, and several hours for it to cool. It might be best used in overnight print runs.
Nylon is hydroscopic, or absorbs moisture. It’s why you’ll see older nylon parts which are yellowed when they were white when new. This isn’t so much an issue, other than cosmetic (and black nylon doesn’t show this at all), in finished prints. But in the powder itself, you get some degradation of the powder the longer it’s left exposed to moisture.
Finally, there’s the problem of shrinkage. Since you’re printing with the whole material being very hot, as it cools, it will shrink. You’ll have to account for this in your final part size. But it doesn’t just shrink. It shrinks differently in the X, Y and Z axes. That makes it complicated to get models that match the designed parameters. For home use, I’m making scale models of real world people or vehicles. Non-consistent shrinkage would be a deal breaker for me. The software, however, does account for this, so it’s possible that this shrinkage can be accounted for and become a non-issue. After all, Shapeways.Com, a trusted 3d print service, uses SLS printing extensively, and they print scale models all the time.
Finally, you can’t just reuse the powder from an SLS print. There’s an awful lot of powder left over, and at best, you can only use a mix of 50% recycled powder and 50% virgin powder. This encourages you to use the most of your build volume. If you can, you won’t have as much left over powder, but I’m sure it does pile up (and I do mean pile up!)
How much do 3d metal printers cost?
3d metal printers are expensive. Far too expensive for home use (at least in 2019), but like everything, that will no doubt change over time. Here are some examples of existing 3d metal printers:
|Example 3d Metal Printer||Approximate Price|
|BeAM Modulo 400||Over $250K USD|
|Formalloy L-Series||Over $250K USD|
|InssTek MX-600||Between $125K and $250K USD|
|Optomec LENS 860||Over $250K USD|
What is the difference between SLA and SLS 3d printing?
Both styles of printing use lasers to fire light into a material to harden it. SLA printers fire lasers at liquid resin to harden it with UV light. SLS printers fire lasers at the surface of very fine powder, already heated to within 10 degrees of its melting point, to push that tiny dot of powder over the melting point and then allow it to cool. SLA liquid UV curing resin is caustic and poisonous to the touch, where SLS powder is safe unless breathed in (common without masks due to the very fine nature of the powder).
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