DefinitionSLA (stereolithography) is a 3D printing process that uses an ultraviolet laser to cure liquid photopolymer resin into a solid part, one thin layer at a time.
Explained
How Does SLA 3D Printing Work?
A laser traces each cross-section of the part on the surface of a vat of liquid resin. Wherever the UV light lands, the resin hardens. The build platform then moves by one layer thickness, fresh resin covers the cured layer, and the next cross-section is drawn on top. Charles Hull's 1986 patent described the method as printing "thin layers of a curable material, e.g., a UV curable material, one on top of the other."
The international standard ISO/ASTM 52900 places SLA in vat photopolymerization, one of seven additive manufacturing process categories. NIST describes the category as forming structures "by curing liquid photopolymer resin with ultraviolet light."
A printed SLA part is not finished yet. It comes off the platform still coated in uncured resin and attached to support structures, which the process needs under overhangs. The part is cleaned, the supports are removed, and it is post-cured under UV light to develop its full mechanical properties.
SLA vs SLS vs FDM
| SLA | SLS | FDM | |
|---|---|---|---|
| ISO/ASTM process category | Vat photopolymerization | Powder bed fusion | Material extrusion |
| Feedstock | Liquid photopolymer resin | Nylon (polyamide) powder | Thermoplastic filament |
| Support structures | Required | Not required | Required |
| Surface finish | Smoothest, finest detail | Slightly rough | Visible layer lines |
| Typical use | Visual models, fit checks, master patterns | Functional parts, snap fits, living hinges | Concept models, large parts, early iterations |
| Tolerance at NICE Rapid | ±0.1 mm (±0.004 in) | ±0.2 mm (±0.008 in) | ±0.3 mm (±0.012 in) |
| Layer thickness at NICE Rapid | 25–100 µm (0.001–0.004 in) | 100–180 µm (0.004–0.007 in) | 100–300 µm (0.004–0.012 in) |
| Lead time at NICE Rapid | 2–3 days | 2–3 days | 1–2 days |
Which SLA Resin Should You Use?
- Standard photopolymer — smooth and rigid but brittle. Best for visual models, fit checks and master patterns for casting.
- ABS-like resin — tougher and more impact resistant, for functional prototypes, housings and enclosures.
- Flexible resin (Shore A 40–80) — elastic and tear resistant, for soft seals, grips and snap-fit trials.
- High-temperature resin (HDT above 180 °C / 356 °F) — for heat-exposed fixtures.
- Castable resin — burns out cleanly, for investment casting patterns.
When to Choose SLA
- Choose SLA when the part is judged by how it looks: appearance models, presentation samples and parts with fine text, thin ribs or small snap features.
- Use it for master patterns. The high-accuracy master for vacuum casting is typically an SLA print, and its surface finish carries straight into the silicone mold.
- Move to SLS or FDM when the part must take repeated load or impact, or when it is bigger than the SLA build volume. At NICE Rapid, that volume is 300 × 300 × 400 mm (11.8 × 11.8 × 15.7 in).
- Mention critical cosmetic faces when you order. Build orientation decides where the support marks land.
Frequently Asked Questions
What does SLA mean in 3D printing?
SLA stands for stereolithography, sometimes expanded as stereolithography apparatus. It is the resin-based 3D printing process in which a UV laser cures liquid photopolymer layer by layer.
What is stereolithography used for?
Stereolithography is used for parts where surface finish and detail matter: visual and appearance models, fit checks, housings, fine-featured prototypes, master patterns for vacuum casting and castable patterns for investment casting.
How accurate is SLA 3D printing?
SLA is the most accurate of NICE Rapid's plastic 3D printing processes. SLA parts are held to ±0.1 mm (±0.004 in) with layer thicknesses of 25–100 µm, compared with ±0.2 mm for SLS and ±0.3 mm for FDM.
Key takeaways
- SLA uses a UV laser to cure liquid photopolymer resin layer by layer.
- It belongs to the ISO/ASTM vat photopolymerization process category.
- SLA produces the smoothest surface finish and finest detail among common plastic 3D printing processes.
- Support structures are required for overhangs, and parts must be cleaned and UV post-cured.
- Resin choice drives part properties, with options including standard, ABS-like, flexible, high-temperature and castable resins.
- SLA is ideal for visual models, fit checks and master patterns for vacuum casting.
Example
Related terms
References
- US Patent 4,575,330 (C. W. Hull), Apparatus for production of three-dimensional objects by stereolithography — patents.google.com
- NIST, Additive Manufacturing: Vat Photopolymerization — nist.gov
- Koltsaki et al., "A Comprehensive Overview of Additive Manufacturing Processes Through a Time-Based Classification Model," 3D Printing and Additive Manufacturing — pmc.ncbi.nlm.nih.gov
- Kafle et al., "3D/4D Printing of Polymers: Fused Deposition Modelling (FDM), Selective Laser Sintering (SLS), and Stereolithography (SLA)," Polymers — pmc.ncbi.nlm.nih.gov