3D Printing Technology Comparison: SLA vs. DLP
Stereolithography (SLA) and Digital Light Processing (DLP) 3D printing technologies follow very similar principles, but can produce significantly different finished 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 into shape using a specific energy light source, solidifying one layer at a time, 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 completely different. Let's delve into what makes them different.
Laser-based SLA and DLP
Based on mirrored industry terminology, we will refer to laser-based technologies simply as "SLA" here. For both SLA and DLP, liquid photosensitive resin is illuminated by light to form a very thin solid surface, which is then stacked to form a complete object.
SLA uses two motors, called galvanometers (one on the X-axis and one on the Y-axis), to quickly aim a laser beam at the print area, causing the resin to solidify into shape. This technique also requires slicing your 3D model into a series of points and lines, which serve as coordinate paths for the galvanometer 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 is 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 two different machines based solely on numerical specifications.
SLA, DLP Build Size vs. Print Speed
DLP can achieve faster print times for certain objects becauseeachlayer is cured with a single flash of light, making it relatively fast. Unlike SLA, which uses a laser spot to form the object, the light needs to follow all paths.
However, DLP's speed advantage is limited to two situations: for large objects with high infill, projection printing will be faster than laser spot printing for each layer. For very small, intricate objects, a smaller projection lens can be used based on the build volume, and finer light spots can be employed to maintain good detail.
Although 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 a full build plate of high-resolution parts. For example, a DLP printer can print a single, perfectly detailed ring faster than an SLA printer. However, to print many detailed rings at once, an SLA 3D printer would be needed to maintain consistent high resolution across the entire print area.
The resolution of DLP printing depends on the projector, which determines the achievable pixel size. For example, full HD 1080p.
The projector in a DLP 3D printer must be focused to an image size to achieve a given X-Y resolution. When small pixels are needed, the entire print area is limited by shrinking the entire image. This means that precise printing on a DLP printer can only use a small portion of the entire print area, while large models can only be printed with low resolution.
The print area of a laser SLA printer 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 built up layer by layer, 3D prints often have visible horizontal layer lines. However, because DLP renders images using rectangular pixels, there are also vertical layer lines.
Notice these lines in the photos below. Vertical layer lines can be found on the surface of DLP prints.
↑↑↑DLP 3D printers use rectangular pixels to render images, which results in a vertical layer line effect. In this image, the vertical layer lines are naturally seen on the left, and the contours are more easily recognizable on the right↑↑↑
Due to their rectangular units, pixels also affect curved edges. Think of building a circle with LEGO bricks – the edges will appear stepped along the Z-axis and in 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 most suitable 3D printing solution for your workflow and printing needs will become easier. In this case, it is important to understand the required surface smoothness of the final print, as well as the object's size and complexity. Here 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 a single detailed object at a time | Printing multiple detailed objects at a time |
| Fast printing of large objects without much detail | Printing large objects with fine detail |
Original text: https://formlabs.com/blog/3d-printing-technology-comparison-sla-dlp/