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Resin 3D printing process: SLA vs. DLP!

This issue will focus on 3D printing resin SLA and DLP technologies, and we will identify their characteristics to establish a comparison between the two processes. While the two technologies have a lot in common, there are also some clear differences. How do these technologies work? What materials can be used? Who are the main manufacturers? We have made a systematic introduction and comparison below.

SLA and DLP technologies

While there are some differences between SLA and DLP printing processes, there are also some similarities between the two. They both expose the liquid photopolymer to a light source. Since they all have a resin tank, they are all designed to print small models with precise details. These methods are compatible with flexible or hard materials, and can also print composites, such as filled glass or ceramics. It should be noted that the printed parts are relatively fragile, easy to deteriorate if exposed to sunlight, and may warp.

Stereolithography (SLA) was the first 3D printing technology developed in 1984 and is now considered one of the most accurate 3D printing processes on the market. Unlike DLP technology, SLA uses a laser light source. A laser beam sweeps through a resin tank that moves on a horizontal axis, curing the material layer by layer. There are now two kinds of machines: one is a machine where the laser works from top to bottom, with each layer having a board that descends with the new layer; The other is a machine where the laser works from the bottom to the top, with a platform that rises as you move. The SLA achieves a smooth surface and a layer thickness of 0.05 to 0.01 mm, allowing objects with extremely thin layers to be printed.

The digital Light processing method (DLP) comes from image projection technology (dating back to the 1980s), using a projector as a light source. In this way, a single cast light affects the entire resin tray at once. At the heart of this process is a digital micromirror device (DMD) that sits between the projector and the resin. It is individually controlled and activated by several microscopic mirrors: if they are active, they reflect light onto the resin and photocured. Therefore, they produce a mask that hardens the resin according to the desired model. Some 3D printers have now replaced the DMD with an LCD screen, greatly reducing the price of the machine. However, we will not focus on those solutions today.

The DLP process is considered faster than stereolithography because it does not work point-by-point. In addition, DLP printers are larger due to their projectors. In most cases, the resin tank on the DLP machine is a little shallower than the one used in the SLA process.

Finally, the final difference between SLA and DLP technologies is in the area of maintenance. DLP printers require little maintenance and are generally easier to service, and the presence of lasers in SLA machines has a lot to do with this.

First, print quality

Print quality is often the deciding factor in choosing between the two technologies. Especially if 3D printing is to be used to produce finished parts, it means that the level of detail, structure, and surface plays a very important role. In principle, these two techniques make it possible to design accurate, high-resolution models at the finest level. However, it is not only the process itself that plays a decisive role in print quality, but also the choice of materials. The latter tends to depend on the manufacturer, and most machines are closed in terms of compatibility.

When printing with the SLA process, the resin is polymerized point by point on the printing bed. The longer the part, the longer the printing time required, because the laser must pass through the entire bed surface. Therefore, SLA is more suitable for printing objects between a few millimeters and 1.50 meters in length. However, there is no loss of mass due to length, and Z resolutions of up to 25 microns can be achieved: they are all independent of model size.

DLP technology allows layers to be up to 5 microns thick. However, it is important to note that due to the projection of pixels, DLP 3D printers produce a “stepped” phenomenon on the final product, which affects the final surface of the printed part. When printing long parts, quality loss can occur on the side. The center of the plate does receive the most concentrated energy from the projector; Then its light spreads around the edges.

Second, technical characteristics

1. Printing speed

In terms of print speed, DLP technology is leading the way. Since DLP cures the entire resin layer at once, the printing process is much faster. Unlike the SLA process, in which the resin is polymerized point by point, in the DLP process, only the height of the part affects the printing speed.

2. Print quantity

Stereolithography is not necessarily used to produce large parts because of the high cost of materials compared to other processes such as FDM. In addition, the amount of printing is limited by the size of the jar containing the liquid resin.

The Formlabs 3L SLA printer has a build volume of 335 x 200 x 300 mm and the 3D Systems Pro X 950 has a build volume of 1,500 x 750 x 550 mm. For DLP printers, the Envision TEC Xtrem 8K machine has a build volume of 450 x 371 x 399 mm and the Carima DM400A model has a build volume of 400 x 330 x 500 mm.

3, post-processing

Post-processing of parts is mandatory in all resin 3D printing processes. This is due to the need for support structures when printing very thin models, which must be removed after curing. This step can be time-consuming and can be one of the main disadvantages of resin 3D printing. The differences in post-processing are mainly related to the materials used, and this is true in both SLA and DLP processes. In addition to cleaning the liquid resin parts with isopropyl alcohol (IPA) or tripropylene glycol monomethyl ether (TPM), this includes drying, removal of support structures, possible post-curing, and, if necessary, sanding and painting of the parts.

In principle, post-processing in SLA and DLP processes is not only time-consuming, but also requires a certain level of expertise on the part of the user, or should be left to the experts. Post-processing in 3D printing is often a challenge for users, which is why some companies have specifically optimized or automated this step.

3. Application cases

When it comes to use cases, SLA and DLP technologies are mostly used in similar industries. In particular, the jewelry and dental sectors often use resin 3D printing. For example, manufacturer Formlabs offers a variety of resins for use by medical professionals. Many companies use them to make various types of medical devices, such as surgical guides. However, due to the wide variety of materials available, many other sectors also use resin 3D printing. Whether for prototyping, injection molding, or even engineering, several suitable resins exist.

4. Major manufacturers

At present, there are some 3D printer manufacturers have turned to SLA technology. One of the main manufacturers is still 3D Systems, a company founded by Charles Hull. But over time, other manufacturers emerged. Formlabs, in particular, has established itself as one of the leaders in SLA 3D printers. In addition to SLA machines, the US company also offers several resins and materials, such as Castable Wax40 resin for the dental sector. With its XFAB printer family, manufacturer DWS also offers machines based on stereolithography technology.

When it comes to DLP 3D printers, EnvisionTEC, a company founded in 2002, is considered a pioneer in the technology. And like B9 Creator and Asiga, some companies then seized on the DLP process to develop their printers. We can also mention those manufacturers who rely on the DLP process to provide faster technology. Carbon 3D has digital light synthesis technology (DLS), which can control the flow of oxygen or photo-centric, and daylight polymer printing (DPP). Prodways, a French company, has patented a DLP-like process called MOVINGLight technology.

5. Price

In most cases, the price of DLP printers is lower than the SLA. But as with all series of 3D printers, it’s important to distinguish between desktop printers and industrial printers.

For entry-level SLA printers, the easiest machine to use is Formlabs’ Form 2. Form 2 has a print size of 145 x 145 x 175 cm and has a point accuracy of about 145 microns. The machine starts at $2,400 and has been on the market since 2015. Note, however, that the American manufacturer has since developed a new range consisting of Form 3 and Form 3L.

On average, SLA 3D printers cost between $3,000 and $4,000. However, if you are looking for industrial machinery, the price will rise dramatically. For example, 3DSystems’ industrial SLA solution has a market price of $500,000. Also, note that machines with lasers working from top to bottom will generally be more expensive.

DLP 3D printers are much easier and attract many additive manufacturing enthusiasts. Anycubic sells several DLP machines for close to $200, as is the case with its Photon Zero printer. Machines used by professionals, including those EnvisionTEC offers for the dental and jewelry industries, cost around $15,000. But as ever, prices vary depending on the manufacturer. Manufacturer Asiga also offers DLP 3D printers for professionals, but they cost around $1,000.

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