SLA 3D Printing
Also: SLA, stereolithography, resin 3D printing, vat photopolymerization, DLP printing, digital light processing, MSLA, resin printing
SLA 3D printing cures liquid resin with a UV laser for the finest detail and smoothest surface: cosmetic prototypes, clear parts and casting patterns.
771 3D printing companies in the Noramark directory
Stereolithography (SLA) builds parts in a vat of liquid photopolymer. A UV laser, or a projector or LCD mask in the DLP and masked-SLA variants, cures each cross-section onto the part as the platform steps one layer, typically 25-100 µm (0.001-0.004"). Parts grow on thin supports, are washed in solvent to remove uncured resin, and are post-cured under UV light and heat to reach their final properties.
SLA gives the finest detail and smoothest surface of the common printing processes: sharp edges, legible small text, thin walls and features around 0.2 mm (0.008"). That makes it the choice for appearance models, fit checks on small parts, clear light pipes and flow-visualization models, master patterns for silicone molds and urethane casting, and hollow investment-casting patterns. Parts sand, prime and paint well, and clear resins polish to near-optical clarity.
The limits come from the material. Photopolymers are thermosets: most are more brittle than the thermoplastics they imitate, creep under sustained load, soften at modest temperatures unless a high-temperature grade is chosen, and yellow and embrittle under UV exposure over months. Supports leave small marks that must be sanded off. Use SLA to see and handle a design, and SLS, MJF, FDM or machining for parts that must carry load or live outdoors.
At a glance
| Typical tolerances | Standard ±0.1 mm (±0.004") up to about 25 mm (1"), plus roughly 0.1% of the dimension beyond that; ±0.05 mm (±0.002") with care on small features printed at fine layers. Long, thin and flat parts warp during post-cure, so flatness is the weak point; holes and fits that matter are drilled or reamed after printing. |
|---|---|
| Size limits | Desktop and mid-size machines build parts 145-350 mm (6-14") on a side; large-frame machines at service bureaus reach about 650 x 750 x 550 mm (26 x 30 x 22"), and the largest about 1,500 x 750 x 550 mm (59 x 30 x 22"). Minimum feature about 0.2 mm (0.008"); walls 0.5 mm (0.020") where supported and 1 mm (0.040") where free-standing. |
| Surface finish | As-printed 1-4 µm Ra (40-160 µin) with faint layer lines, smoothest on up-facing surfaces; support points leave small nubs that are sanded flush. Wet sanding and polishing reach 0.2-0.4 µm Ra (8-16 µin), and clear resins reach near-optical clarity with polishing and a clear coat. Parts take primer and paint for appearance models. |
| Lead time | Raw prototypes in 1-3 business days, often overnight; sanded, painted or polished clear parts in 5-10 business days; batches of small parts in about a week. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Resin families rather than named plastics: general-purpose resins; tough resins that imitate ABS or polypropylene; clear and polycarbonate-like resins (Somos WaterShed, Accura ClearVue); high-temperature resins with heat deflection above 200 °C (390 °F); flexible and elastomeric resins; ceramic-filled resins for stiffness; castable wax-filled resins for jewelry and dental work; and biocompatible grades for surgical guides. The ABS, polycarbonate and acrylic links point to the production plastics these resins stand in for during prototyping; the printed part is a thermoset with its own, lower toughness and heat resistance. Ask for the resin by name and check its data sheet for heat deflection, elongation and impact.
What drives the cost
- Build height and layer thickness: tall parts and fine layers take longer
- Part volume and resin price: clear, high-temperature, ceramic-filled and biocompatible resins cost more
- Support removal and sanding labor, especially on cosmetic surfaces
- Cosmetic finishing: primer, paint, texture, polishing and clear coat
- Size: large-frame machines bill at higher hourly rates
- Quantity: several small parts can share one build
When to use it
- Appearance models and presentation prototypes with sharp detail and smooth surfaces
- Fit checks on small, detailed parts such as connectors, knobs and device housings
- Clear parts: light pipes, visual-check lenses and flow-visualization models
- Master patterns for silicone molds and urethane casting, and investment-casting patterns
- Dental, jewelry and microfluidic parts with fine features
When not to
- Functional parts under sustained load, impact or repeated flexing: SLS or MJF nylon is tougher
- Outdoor or sunlit service: most resins yellow and turn brittle under UV
- Service above the resin heat-deflection temperature, often below 80 °C (175 °F) for standard resins
- Large, flat, thin panels, which warp during post-cure
- Production volumes: molding or MJF costs less per part
Design tips
- Tell the shop which faces are cosmetic so they are oriented away from supports.
- Hollow large parts to a 2-3 mm (0.08-0.12") wall with at least two drain holes of 3-4 mm (0.12-0.16") to save resin and avoid trapped uncured resin.
- Keep walls at least 0.5 mm (0.020") where supported and 1 mm (0.040") where free-standing, and thicken long, thin features.
- Do not print fine threads for repeated assembly: tap them or bond in threaded inserts, because heat-set inserts do not melt into a thermoset.
- Name the resin, or the property you need (heat deflection, elongation, clarity), instead of just writing SLA.
- Add ribs to long, flat sections, or split them, to limit warping in post-cure.
- For clear parts, say whether you need see-through clarity; it takes hand sanding, polishing and clear coat, which is quoted separately.
Frequently asked questions
- SLA vs FDM: which should I use?
- SLA for detail and surface: small parts, smooth cosmetic models, clear parts and casting patterns. FDM for size, cost and tougher thermoplastics: large prototypes, fixtures and parts in ABS, nylon, Ultem or PEEK. For a functional plastic part that needs both detail and toughness, look at SLS or MJF nylon.
- How strong are SLA printed parts?
- Stiff but brittle next to molded plastics. Standard resins reach tensile strengths similar to or above ABS, roughly 40-65 MPa (6-9 ksi), but elongation at break is only about 5-15%, and tough resins trade stiffness for more stretch. They creep under constant load and lose toughness with UV exposure, so treat SLA parts as prototypes unless the resin data sheet and a test say otherwise.
- Do SLA prints yellow in sunlight?
- Most do. UV light keeps reacting with the resin, so parts yellow and become more brittle over weeks to months outdoors or near a window. A UV-stable paint or clear coat slows it; for outdoor functional parts, choose ASA by FDM, or coated nylon by SLS or MJF.
- Can SLA parts be used as investment casting patterns?
- Yes. Hollow, honeycomb-filled SLA patterns (3D Systems QuickCast) and castable resins burn out of the ceramic shell like wax, and foundries use them for prototypes and low volumes without pattern tooling. Ask the foundry which pattern type and resin it accepts, since solid resin expands during burnout and can crack the shell.
- How accurate is SLA printing?
- About ±0.1 mm (±0.004") on features up to 25 mm (1") and roughly 0.1% beyond that, with ±0.05 mm (±0.002") possible on small features. Post-cure shrinkage and warping on long, flat parts are the main sources of error.
