SLA Has Arrived!

As a nearly lifelong 3D printing nerd, I have always dreamed of working with the sorts of machines and people that are now at POP.  Uncrating our first F900-class machine was an especially magical moment, which had taken almost 10 years of slow and steady growth to achieve.​

Recently, we had a similarly joyous occasion when we finished our first print on the Projet SLA system that was installed at POP.  Until this point, we had avoided SLA -- between our focus on FDM and Polyjet, we often felt there wasn't much of a need for such a system.  But more and more projects were coming our way that weren't quite perfect matches for either FDM or Polyjet, and the need for in-house SLA started to feel undeniable.  

While the resolution and materials are similar to PolyJet, there are some key differences:

• SLA builds are strictly single material
• SLA builds don't use a dedicated support material

The second point has some major implications, both good and bad.  Without a dedicated support material, necessary supports are made of, you guessed it, model material -- and have to be physically separated from the final part.  This can be a bit of a pain and leave minor cosmetic blemishes -- but in the context of industrial SLA is minimized because very few supports are needed in the first place.  Virtually no mechanical forces exist during the printing process: the model is neutrally buoyant in the vat of resin, there are no peeling forces to contend with (parts sink layer by layer into ​the vat as they're building), and curing is done with a laser that never pushes the part around like FDM nozzles might.  The lack of support material also means that very small and/or thin features are more likely to succeed with SLA vs Polyjet, since there is no boundary layer to deal with, or inadvertent mixing of model and support materials which can slightly weaken layer interfaces (SLA parts are very nearly isotropic).  

In light of these points, one strong application for SLA printing are parts with internal geometries (thin microfluidics) where precision and water-tight prints are a requirement. Other applications include cosmetic parts which aren't ideal for Polyjet (thin wall and large models are generally more suitable for SLA).  

We decided to kick things off with a highly intricate chameleon model.  It's solid infill (generally not a problem for SLA, other than cost), and measures almost one foot long in total.  

The printing process starts with slicing and support generation.  For the purposes of this test, I wanted to pick an orientation that would generally be avoided for SLA: lying horizontally.  Speaking on the whole, it's hard for SLA systems to produce large flat sheets (XY plane); such surfaces can tend to pull/distort very slightly as they sink into the vat and lead to artifacts that are avoided if the model is tilted instead.  But since there aren't really any large flat surfaces in this model, I wasn't feeling as worried about it -- and tilting up would increase the print time drastically.  

Next up comes the fun part: printing!  We used Accura Xtreme Grey for this build.  It's a nice neutral tone, and among the most mechanically tough resins out there, with a healthy temperature tolerance to match (~70C) -- we don't want this guy getting droopy during the summer!  

The two clips below show the general process: a laser beam (either a fine spot for edge details or larger for infill) traces and scans across the resin at blazingly fast speeds to precisely cure the resin into a solid model.  The print bed (within the resin) then sinks by the layer thickness (0.004" in this case) and the recoater blade wipes fresh resin across the top of the vat (so that we get a flat surface and don't need to wait for resin to creep into the thin void).  Then the laser process starts anew.  

Finally, about 15 hours later, it's time for the big reveal!  The platform ascends out of the vat and drains excess resin back into the tank for use during a future print.  A truly mesmerizing sight to see!  

Then comes the cleaning -- the least exciting part!  The tray is removed from the printer, and the part is scraped off of it.  Using detergents, brushes, ultrasonic, and several rinses, the model is cleaned of any residual uncured resin and left to dry for several hours. More supports are also removed at this stage, mostly by brushing them off (as mentioned earlier, SLA supports are quite fine).  

Finally, it's time for post-curing.  Although the laser did the vast majority of the curing work already, a quick post-cure in our UV chamber helps to ensure that resin is fully cured, for best mechanical properties as well as to lessen any surface tackiness that could remain on freshly washed models.

And voila: the final result!