Comparison: SLA vs. DLP
Mirroring industry terminology, we’ll here to refer to laser-based SLA simply as “SLA.” For both SLA and DLP, a vat of photo-reactive liquid resin is selectively exposed to light in order to form very thin solid layers that stack up to create one solid object.
SLA uses two motors, known as galvanometers or galvos, (one on the X axis and one on the Y axis) to rapidly aim a laser beam across the print area, solidifying resin as it goes along. This process breaks down the design, layer by layer, into a series of points and lines that are given to the galvos as a set of coordinates.
DLP uses a digital projector screen to flash a single image of each layer across the entire platform at once. Because the projector is a digital screen, the image of each layer is composed of square pixels, resulting in a layer formed from small rectangular bricks called voxels.
The fact that the basic units of the two processes are different shapes makes it difficult to compare the different machines by numerical specifications alone.
Dig into what 3D printer specs really mean, and get tips for effectively evaluating which 3D printer is right for you.
Print Size vs. Speed in SLA and DLP
DLP can achieve faster print times for some parts, as each entire layer is exposed all at once, rather than drawn out with a laser.
This faster print time applies in two cases. For large, fully dense prints, where the print will fill up much of the platform, each layer is exposed faster than it would be if drawn out by a laser. For very small, finely detailed prints, it can be possible to swap out projector lenses according to the area of build volume, and consequently use a narrow amount of light to more quickly build small layers.
Though faster, printing full volume with DLP introduces trade-offs in resolution and surface finish, whether with large parts or sets of many smaller, finely detailed parts.
Read more about understanding X-Y resolution, and understanding Z resolution.
DLP resolution depends on the projector, which defines how many pixels/voxels are available. For example, full HD is 1080p.
The projector in a DLP 3D printer must be focused to an image size in order to achieve a given X-Y resolution. When small pixels are desired, this constrains the overall build area by shrinking the entire image. That is, a detailed print on a DLP printer must only use a fraction of the overall build area, and large models can only print at a coarse resolution.
DLP 3D printers are restricted by pixel size. A printer that has a large build volume has a fixed amount of large pixels, making it impossible to print small details at full build volume.
A laser SLA printer’s build volume is completely independent from the resolution of the print. A single print can be any size and any resolution at any location within the build area.