Most people may know FDM technology, which is the most famous 3D printer technology at present. If you want to start learning 3D printing. FDM technology will be a good choice. But when it comes to molding utilities, DLP technology is more complex and more suitable for dental or jewelry molds. Resin 3D printing is known for its ability to achieve very fine, highly refined parts thanks to a technology called barrel polymerization.

What is barrel polymerization technology? DLP means digital light processing. A technique may utilize a photosensitive polymer resin (liquid) capable of curing (curing) under a light source. In the field of barrel aggregation, there are two main technologies: SLA and DLP. Of course, both of them are parts made of resin and light source. The main difference is the type of light source used for curing resin.

In the following sections, we will provide more detailed descriptions of SLA and DLP.

Process

SLA 3D printer consists of a barrel (a resin tank), a construction platform, an elevator for moving the construction platform up or down, a light source and a pair of galvanometers.

The printing process starts with pouring resin into the barrel to form a layer between the construction platform and the bottom. After the construction platform is placed in place, the light source shines through the transparent cylinder bottom to solidify the resin.

The light source in most SLA 3D printers is a solid-state laser. When the laser hits the current detector, they ensure that the beam is accurately navigated along a specific pattern. When the laser beam "touches" the resin tank, it will cure the resin at that specific point.

When the laser completes the single-layer curing process, the height of the construction platform will rise one layer, and then repeat the process until the part is completed.

SLA printer type

It is worth mentioning that there are two types of SLA 3D printers, depending on the moving direction of the construction platform and the location of the light source.

The above description refers to the SLA 3D printer of "bottom-up". This is because the light source of the bottom-up SLA 3D printer is located under the resin tank. When viewing the timing video of a running bottom-up SLA 3D printer, it appears that the part has been pulled out of the resin can.

Another type is the so-called "top-down" SLA 3D printer. Here, the light source is located above the resin tank and the construction platform. When starting 3D printing on a "top-down" SLA 3D printer, there is only one layer of resin on the build platform. After the light source solidifies the layer, the construction platform will move down into the barrel, which means that the final part will be completely immersed in the resin.

DLP 3D printer

As mentioned above, the only difference between DLP and SLA 3D printers is the light source used to cure the resin.

Technology

The light source used by DLP 3D printer is digital projector screen. In SLA, laser can only solidify one point at a time, while DLP printer's screen can project the image of the whole layer at a time. As a result, DLP printers typically print faster than SLA printers.

The device used to control the position of light projection in DLP 3D printers is called digital micro mirror device (DMD). It's a bit like a galvanometer in an SLA printer, but it's much more complicated.

DMD is the "heart" of each DLP chipset. DMD contains thousands or even millions of tiny mirrors that guide light and create layers of patterns.

Since the DLP 3D printer uses the digital projector screen as the light source, the image of the layer is composed of pixels. Once they are 3D, they become voxels - tiny rectangular prisms visible on all three axes.

Process

The printing process of DLP is the same as SLA, pouring the construction platform into the bucket, keeping only one layer of height between itself and the bottom of the bucket. When the image of the layer flickers, it solidifies the resin that forms the solid layer. The build platform moves up and repeats the process until the part is complete.

So far, we've only mentioned the benefits of DLP 3D printers over SLA machines: increased speed. As you might expect, DLP also has its limitations.

Because DLP 3D printers use digital projector screens, it is difficult to print large and detailed parts with their complete manufacturing capacity. In order to obtain highly refined components, the image size of the projector flicker must be small enough to not see a single pixel.

To fully understand this, suppose you increase the size of the picture on your smartphone. As pictures grow, quality is sacrificed. This is why DLP is not suitable for making a large detailed picture or printing many detailed objects with its full build volume.

Another limitation of DLP printers is the square surface finish. Because voxels are rectangular, the curved part of the printed matter often does not have a very smooth finish compared to SLA. The advantage is that you can solve voxel and curve problems by grinding parts after printing.

DLP and SLA printers use resins, so the cost of printing should be similar. However, keep in mind that the cost depends a lot on the manufacturer of the resin and even on the 3D printer.