Resin 3D printing is known for its great ability to achieve very nice, highly detailed parts, all thanks to a technology called vat polymerization, which is more complex than fused deposition modeling (FDM), the most common (and least expensive) 3D printer technology.
Vat polymerization utilizes a photopolymer in the form of a viscous fluid, resin, and a light source to cure the resin and therefore build the desired parts.
There are two main types of vat polymerization technology: stereolithography, or SLA, and digital light processing (DLP). The primary difference between the two is the light source used to cure the resin and produce a desired part.
Before we go into more detail about how “UV resin 3D printers” work and the technology behind them, we should first say that “UV resin 3D printer” isn’t a proper term, despite often being searched on the web. The proper term for 3D printers that make of resin is simply “resin 3D printer”. Indeed, DLP 3D printers don’t even use UV light.
In the following sections, we’ll provide a more detailed explanation of both SLA and DLP.
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Although many people might think FDM is the first 3D printing technology, that title actually belongs to SLA.
An SLA 3D printer consists of a vat (a resin tank), a build platform, an elevator — used for moving the build platform upwards or downwards — a light source and a pair of galvanometers.
The printing process starts with the resin being poured into the vat so that there’s a single layer between the build platform and the bottom. After the build platform is in place, the light source shines through the bottom of the vat, which is transparent, to cure the resin.
The light source in most SLA 3D printers is a solid-state laser. When the laser hits the galvanometers, they ensure that the beam is precisely navigated along a particular pattern. When the laser beam “touches” the resin tank, it cures the resin at that specific point.
When the laser finishes the curing process of a single layer, the build platform is elevated by one layer in height and the process is repeated until the part is complete.
Types of SLA Printers
It’s worth mentioning that there are two types of SLA 3D printers, depending on the direction the build platform moves and where the light source is placed.
What’ve described above refers to “bottom-up” SLA 3D printers. That’s because the light source of bottom-up SLA 3D printers is positioned under the resin tank. When looking at a timelapse video of a bottom-up SLA 3D printer in operation, it looks like the part is being pulled from the resin tank.
The other type is the so-called “top-down” SLA 3D printer. Here, the light source is positioned above the resin tank and the build platform. When starting a 3D print on a “top-down” SLA 3D printer, there’s a single layer of resin on the build platform. Once the light source cures that layer, the build platform moves down into the vat, meaning the final part will be completely submerged in resin.
As we’ve already mentioned above, the only difference between DLP and SLA 3D printers is the light source used to cure the resin.
The light source DLP 3D printers use is a digital light projector screen. Whereas in SLA, a laser cures only a single point at a time, a DLP printer’s screen projects the image of an entire layer all at once. As a result, DLP printers generally print faster than SLA printers.
The device used for controlling where light is projected in DLP 3D printers is called a digital micromirror device (DMD). This is sort of like the galvanometers in an SLA printer, but much more sophisticated.
The DMD is at the “heart” of every DLP chipset. A DMD contains hundreds of thousands or even millions of small micromirrors that direct the light and create the pattern of a layer.
Since DLP 3D printers use digital light projector screens as a light source, the image of a layer is made out of pixels. Once 3D , these become voxels — tiny rectangular prisms visible in all three axes.
The process of printing for DLP is the same as with SLA, the build platform is poured into the vat leaving only one layer in height between itself and the bottom of the vat. When the image of a layer flashes, it cures the resin forming a solid layer. The build platform moves up and the process is repeated until the part is complete.
For more of the same, check out our article on DLP 3D printers.
To conclude the article, let’s pit SLA against DLP.
It’s true that DLP printers are faster than SLA printers, but there are a few caveats. One problem with DLP is that they’re not very good at producing prints that are both highly detailed and large. That’s because the same DMD must be used to cover a wide print area. The maximum number of pixels doesn’t change, but the area they’re spread over does.
Another issue with DLP is that the voxels in a 3D print result in a much less fluid surface, especially for “organic” models.
For a more in-depth comparison, check out our DLP vs SLA shootout.
License: The text of "UV Resin 3D Printer – What Is It?" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.
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