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SLA vs DLP: Guide to Resin 3D Printers
Scott Gabdullin
Updated on November 15, 2023
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In recent years, 3D printing has become more affordable and accessible, rising in popularity among businesses and individuals. 3D printing, also known as additive manufacturing, allows manufacturers to speed up production times and lower production costs. However, for many, 3D printing is relatively new and can be intimidating to begin understanding.
The most common resin 3D printing processes are stereolithography (SLA) and digital light processing (DLP). This guide will cover the main differences and similarities between SLA and DLP resin 3D printers.
This guide will also help those who aren’t novices in the 3D printing world but might need guidance on finding the perfect process for their production needs.
Table of Contents
What Are SLA And DLP Resin 3D Printers?
SLA and DLP printing use a light source against liquid resin to form layers of hardened plastic. When done correctly, resin printing is well known for the smooth, accurate, and airtight materials it can create. This plastic is carefully stacked to create a solid object. SLA and DLP resin 3D printers create objects, products, prototypes, or parts that their operators first create digitally.
On the surface, each of these machines produces similar products. However, they each have unique processes and materials that go into the printing of their products. As a result, the products they print can have a variety of outcomes.
It is important to know even the smallest details and differences between these two printers to understand which printer is the most efficient for your needs.
What Is SLA Resin 3D Printing? How Does It Work?
Stereolithography resin 3D printing is the original 3D printing process. Despite this, SLA 3D printers are still the most popular for 3D printing. Traditionally, these printers were expensive and difficult for non-expert users, but recent advancements have made them more accessible, affordable, and of higher quality.
As previously mentioned, these machines take a liquid resin and turn it into hard plastic through a light source. However, for SLA printing, a laser is used for the light source. This is different from the light source utilized by DLA resin 3D printers. The UV light from the laser initiates the polymerization process necessary to cure the liquid resin.
The resin sits in a non-stick surface tank that allows the liquid resin to harden without sticking to the surface around it. The liquid resin carefully separates from the newly formed layers. A build platform is the part of the printer that goes into the resin tank to make the layers. The platform can move up and down to let more resin in after the printer forms a layer.
During the printing process, the build platform lowers into the resin tank leaving just enough space for the layer height. Once the platform lowers into the resin, the laser cures the photopolymer resin by pointing at two mirror galvanometers. The galvanometers direct the laser to the points of the layer. The laser slices through the resin point by point.
After the laser cures the layer, the layer detaches from the tank while the build platform rises to allow more resin to flow. The process starts over again until the printing has finished.
SLA Advancements
The next phase of SLA 3D printing is Low Force Stereolithography (LFS). This phase is more advanced and accessible for everyday users. With a more flexible tank and a high-density linear laser, the LFS process reduces the pressure exerted on the resin and materials during the printing process.
A Light Processing Unit (LPU) contains the light source, where the galvanometer positions the laser perpendicular to the LPU on a Y axis and through a spatial filter. Then, the galvanometer directs the laser to a fold mirror and a parabolic mirror.
These mirrors allow the laser to consistently remain perpendicular to the build platform, creating more accurate layers. This process is much less abrasive on the materials. As a result, the end product is higher quality, smoother, and more accurate.
What Is DLP Resin 3D Printing? How Does It Work?
Digital light processing 3D printers utilize a similar resin tank and build platform process as standard SLA resin 3D printers. The build platform lowers into the resin tank and rises afterward. However, what makes the DLP resin 3D printing process different is the light source.
While the SLA resin 3D printer cures a layer by going through each point individually, the DLP resin 3D printer utilizes a digital projector screen. The digital projector screen flashes an image of the desired layer across the platform, curing each point simultaneously and synchronously forming the entire layer.
The light is projected and reflected onto a Digital Micromirror Device (DMD). The DMD consists of microscopic mirrors on a semiconductor chip. The mirrors quickly move between the lenses directing the light to reach the coordinates of the image and form the layer.
These processes seemingly reach the same goal: curing the resin. However, because the DLP printer uses a screen to flash the image, the physical layer consists of small rectangular cubes called voxels that were initially square pixels in their digital form.
Resolution
Resolution is a common buzzword when discussing resin 3D printing capabilities. SLA and DLP printers use different shapes for their resolution units, so it’s important to understand these differences before comparing the two.
3D printing deals with three dimensions, X and Y which are planar 2D dimensions, and the third vertical dimension Z. The Z dimension makes 3D printing what it is.
Both SLA and DLP printers provide users with superior Z resolutions compared to other 3D printing processes, as they can create the thinnest layers with a wide range of options for layer height. SLA and DLP printers differ in their X and Y units.
Resolution is important in some ways, but it doesn’t always predict the accuracy, precision, and quality of the printing.
SLA Resolution
For SLA printers, the point size of the laser and the increments in which it is moved and controlled determine the XY resolution of the SLA printing.
Through the line scanning process in LFS SLA printers, the laser can move in small increments creating smaller parts and better resolution. This means an 85-micron spot size laser can create parts with 25-micron XY resolution.
DLP Resolution
For DLP printers, the pixel size determines the XY resolution. The pixel size is the smallest part the projector can create with one layer. The projector resolution determines the XY resolution of the DLP printer, usually a fixed amount that cannot be changed. A typical DLP projector is full HD, 1080p. A common fixed resolution range for DLP resin 3D printing is between 35 to 100 microns.
Accuracy
Accuracy and precision are some of the most crucial aspects to consider regarding 3D printers. The accuracy and precision of a resin 3D print are dire for creating products such as surgical guides, dental splits, and joint replacements. Of course, they are also crucial for creating the exact prototype or end product that the operator desires.
As an additive process, 3D printing comes with the risk of inaccuracy as each layer is added on. For optimal accuracy, a printer should be able to print and deliver each layer the same way in the precise location necessary. To ensure each layer comes out accurate, precise, and of quality, the operator needs to focus on many factors, including:
- Materials
- Process
- Settings
- Post-processing
- Calibration
Even though SLA and DLP printing differ in process, each is among the most accurate and precise of all 3D printing processes available. Usually, if SLA and DLP products differ in accuracy, precision, or quality, it is due to the manufacturer, not the technology.
The materials and parts that go into the 3D printing process can vary widely, creating different results depending on the quality of the materials.
To understand what works best for your printer, talk to the manufacturer and evaluate each part yourself to ensure it is correct for the print you need to complete. Even different resins can alter the accuracy and precision of a print if they do not have the correct parts to go along with them.
Each printing process offers its benefits with precision and accuracy. Choosing a DLP resin 3D printer rather than an SLA resin 3D printer will not immediately determine whether or not your print will be more or less accurate. Instead, it is important to educate yourself and talk to the manufacturer to ensure you have what you need to produce a precise print.
SLA Build Volume
SLA resin 3D printers can create products with an unlimited build volume, without compromising resolution.
Unlike DLP printing, the resolution and the build volume of SLA printing are controlled separately. With this capability, SLA printing allows users to create large products with high resolution or a large number of small products.
Although expanding the build volume exerts more force on the layers and thus risks complications or accuracy, the advanced LFS SLA printing maximizes the build volume with a more gentle exertion.
DLP Build Volume
DLP resin 3D printers, especially those that are affordable and accessible, often specialize in either resolution or build volume, not both. This means that a DLP resin 3D printer that can produce high-resolution prints will have a smaller build volume, only able to create small parts and products.
Meanwhile, a DLP resin 3D printer with a lower resolution will have a higher build volume, creating larger products and prints.
The only way to increase the build volume while maintaining high-resolution on DLP printers is to utilize a 4K projector or stack projectors next to each other.
Finishes
DLP and SLA printing create smooth finishes. The difference in their finishes is only in the fine details.
Due to resin 3D printing forming their prints through a layering process, small horizontal lines are sometimes present in the finish. For DLP printing, vertical voxel lines may also be present due to the pixels used to cure the resin. Additionally, for curved prints, the rectangular units of DLP printing make curved edges appear stepped.
The curves are not smooth or round as they were formed through rectangular layers. To smooth them out, if desired, one would need to sand the edges or engage in another form of post-processing. With advanced SLA printing, such as LFS, the layer lines are much less visible and smoother. The reduction in force from the LFS minimizes surface roughness.
SLA Speed
SLA printers carefully draw each point of a layer with their laser. So, for larger prints, SLA printers may be slower than other 3D printers, such as a DLP printing process. However, for small or medium-sized prints, especially those with more detailed pieces, an SLA printer is around the same speed or faster than a DLP printer.
Although the laser’s careful process may seem slow, SLA printers can adjust their build volume to almost any need of their user, making them more efficient with throughput.
DLP Speed
DLP printers allow users to create layers with a flash of the projector, hitting each point simultaneously. As a result, DLP printers create layers faster than most resin 3D printers. DLP printers are faster at creating large dense prints. However, due to their limitations in build volume, users are limited in the size of parts they can create and the throughput of the machine.
Materials
Materials change the speed, resolution, and even accuracy of a product. Most DLP and SLA printers come with easy-to-use materials that can be replaced with more advanced equipment if and when desired.
There are even some advanced resin tanks that can automatically refill the tank. There is even a wide range of resins to create different prints. Some resins even allow for faster output and are often used to create prototypes of products.
The more advanced a person gets at 3D printing, the more advanced the product they will want to create. Understanding both DLP and SLA resin 3D printing and the materials that go into them allows users to maximize their production goals and become experts in the industry.
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Scott Gabdullin
Scott Gabdullin is a Canadian entrepreneur, investor, and marketing expert who has successfully combined his passion for technology and innovation with a love for adventure and exploration.
Scott brings 12 years of digital marketing experience and a hardcore work ethic to his new passion for 3D printing. If he is not working on this business, he is likely travelling and Overlanding across North America with his wife and 2-year-old son in their Jeep Rubicon.
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