The level of detail an SLA printer can produce is dependent on the laser spot size and resin properties. General guidelines for designing for SLA are as follows:
SLA is able to achieve much higher resolutions than FDM because it uses a laser to solidify the material. SLA printing resolution in the XY-direction (or horizontal resolution) is dependent upon the laser spot size and can range anywhere from 30 to 140 microns. This is not an adjustable parameter of printing. The minimum feature size cannot be smaller than the laser spot size.
Resolution in the Z-direction (or vertical resolution) varies from 25 to 200 microns. Choosing vertical resolution is a trade-off between speed and quality. For a part that has few curves or fine details, there will be little visual difference between a print at 25 microns versus a print at 100 microns. By comparison, a desktop FDM machine will typically print z-axis layers at 150 to 400 microns.
Hollowing and cupping
SLA machines print a solid, dense model but if the print is not intended to be a functional part hollowing the model significantly reduces the amount of material needed as well as print time. It is recommended that the walls of the hollowed print be at least 2 mm thick to reduce the risk of failure during printing.
If printing a hollow part, drainage holes must be added to prevent uncured resin from getting trapped inside the final print. This uncured resin creates pressure imbalances within the hollow chamber, and will cause what is known as “cupping”. Small failures (cracks/holes) propagate throughout the part and will cause complete failure, or part explosion, if not corrected. Drain holes should be at least 3.5 mm in diameter, and at least one hole must be included per hollow section.
Rules of thumb
SLA is ideal for small parts that require a smooth surface finish (comparable to injection molding) and a high level of accuracy.
Support structures are critical to successfully printing accurate SLA parts. If a good finish is required on a surface the part should be orientated so that that surface is not in contact with support material (typically upwards facing).
SLA parts typically have poor mechanical properties and are best suited for non-functional prototyping, enclosures and visual models.
|Supported walls||At least 0.4 mm thick.|
|Unsupported walls||At least 0.6 mm thick|
|Overhangs||Less than 1.0 mm in length and at least 19° from level.|
|Embossed details||At least 0.1 mm in height|
|Engraved details||At least 0.4 mm wide and 0.4 mm thick|
|Connections||0.2mm for assembly connections and 0.1mm for snug fit|
|Holes||Minimum diameter of 0.5mm|
Edited by Shinlocke