3D Printing Technology Comparison: SLA vs. DLP
Stereolithography (SLA) and Digital Light Processing (DLP) 3D printing technologies operate on very similar principles, yet can produce significantly different end products.
Understanding the nuances of each 3D printing process helps to manage user expectations for the final print results and how to effectively maximize the potential of each different machine.
"Stereolithography" comes from the Greek word "stereo," meaning solid, and "(photo)lithography," which is a method of photolithography. In 3D printing, stereolithography refers to using light to create solid objects. SLA technology solidifies liquid resin layer by layer using a specific energy light source, stacking them to form an object.
By definition, both SLA and DLP are stereolithography technologies, but drawing layers with a laser (SLA) and projecting layers (DLP) are entirely different. Let's delve into what makes them different.
Laser-based SLA and DLP
Based on the industry jargon for mirrors, we'll refer to laser-based technologies simply as "SLA" here. For both SLA and DLP, liquid photosensitive resin is illuminated to form a very thin solid surface, which is then stacked to create a complete object.
SLA uses two motors, called galvanometers or galvos (one on the X-axis and one on the Y-axis), to quickly aim the laser beam at the print area, solidifying the resin accordingly. This technique also requires your 3D model to be sliced and broken down into a series of points and lines, which serve as coordinate paths for the galvos to reflect the laser.
DLP uses a digital projection screen to illuminate a single image for each layer on the print platform. Because the projected image comes from a digital screen, each layer's image is composed of square pixels, resulting in each layer being formed by small rectangular blocks called voxels.
The fact that the basic units of the two photopolymerization methods have different shapes makes it difficult to compare the two different machines based on numerical specifications alone.
SLA, DLP Build Size vs. Print Speed
DLP can achieve faster print times for certain objects becauseeachlayer is cured in one go, making it relatively fast.Unlike SLA, which uses a laser spot to solidify, where the light needs to trace all paths.
However, the speed advantage of DLP only applies under two conditions: for large objects with high infill, projection-based printing will be faster than laser spot printing for each layer. For very small, intricate objects, a smaller projection lens can be used depending on the build area, and finer light spots can maintain good detail.
While faster, printing multiple objects simultaneously with DLP technology may affect the resolution or surface integrity of the objects.
DLP 3D printers are not ideal for printing full-plate high-resolution parts. For example, a DLP printer can print a single, perfectly intricate ring faster than an SLA printer. However, to print many intricate rings at once, an SLA 3D printer would be needed to maintain consistent high resolution across the entire build area.
The resolution of DLP prints depends on the projector, which determines the achievable pixels. For example, full HD 1080p.
The projector in a DLP 3D printer must focus on the image size to achieve a given X-Y resolution. When small pixels are needed, the entire print area is limited by scaling down the entire image. This means that precision printing on a DLP printer can only use a small portion of the entire print area, while large models can only be printed at low resolution.
The print area of laser SLA printers is completely independent of the resolution of the printed object. A single object print can be of any size and any resolution at any location within the print area.
Surface Finish: Pixels and Layer Lines
Because objects in 3D printing are composed of stacked layers, 3D prints often have visible horizontal layer lines. However, because DLP renders images using rectangular pixels, there is also a vertical layer effect.
Notice these lines in the photo below. Vertical layer effects can be found on the surface of DLP prints.
↑↑↑DLP 3D printers use rectangular pixels to render images, which results in a vertical layer effect. In this image, the vertical layer effect naturally appears on the left, and the contours are more easily identifiable on the right↑↑↑
Due to the rectangular shape of the units, pixels also affect curved edges. Think of building a circle with Lego bricks – the edges will be stepped along both the Z-axis and the X-Y plane.
↑↑↑The rectangular shape of pixels causes curved edges to appear stepped↑↑↑
After analyzing the differences in technology and results, choosing the 3D printing solution best suited for your workflow and printing needs becomes easier. In this case, it's important to understand the required surface smoothness of the final print, as well as the object's size and complexity. Below are some general guidelines on which types of objects are better suited for DLP and SLA:
| DLP is suitable for | SLA is suitable for |
| Printing single, intricate objects at a time | Printing multiple intricate objects at once |
| Rapid printing of large objects without much detail | Printing detailed large objects |
Original text: https://formlabs.com/blog/3d-printing-technology-comparison-sla-dlp/