SLA — Stereolithography
UV laser cures liquid resin with exceptional precision — delivering the smoothest surface and finest detail of any common 3D printing process.
SLA
Stereolithography
From a vat of liquid resin to a finished part
- UV laser (355 nm) traces each layer onto liquid photopolymer resin.
- Resin hardens instantly — light triggers the curing reaction.
- Platform lifts one layer thickness, pulling the part up from the vat.
- Repeats for thousands of layers until the part is complete.
- Part is IPA-rinsed then UV post-cured to reach final properties.
What SLA is great at — and where it falls short
- Best surface finish of any common 3D printing process
- Captures fine detail down to 0.2 mm
- Tight tolerance — ±0.15 mm
- Nearly isotropic — strong in all directions
- Wide resin range (transparent, high-temp, castable, dental)
- Large build envelope (Uniontech RSPro 1400 = 1400×700×500 mm)
- Brittle unless using Tough resin
- Degrades in UV/sunlight without protective coating
- Multi-step post-processing adds time (wash + cure)
- Higher cost per cm³ than FDM
- Liquid resin is a skin irritant — handle carefully
- Support marks left on downward-facing surfaces
When to choose SLA
- Surface finish is critical (presentation models, customer-facing parts).
- You need detail below 0.5 mm (text, fine features, miniatures).
- You need tight tolerances for mating parts and assemblies.
SLA resins we stock
Standard Resin
The workhorse of SLA printing. Produces high-stiffness, high-resolution parts with a smooth, near injection-moulded surface finish. Affordable and ideal for concept models, visual prototypes, and general-purpose parts where surface quality matters more than impact resistance.
ABS-like (Tough) Resin
Enhanced impact strength and toughness compared to standard resin — properties similar to ABS plastic. Less prone to brittleness, making it the go-to choice when the part needs to handle stress, snap-fits, or repeated assembly. Slightly less surface detail than standard resin.
Transparent Resin
Clear resin that can be polished to near-optical clarity. Balances strength, flexibility, and translucency with minimal moisture uptake. Ideal for any application where seeing through the part matters — light guides, fluid channels, lens housings, and display enclosures.
The numbers that matter
What tolerance means in practice: ±0.15 mm means a 10 mm hole prints between 9.85 mm and 10.15 mm — tight enough for press-fits, dowels, and most mating assemblies straight off the machine. For optical-class parts (lens prototypes, fluidic devices) we recommend modelling 0.1 mm under-size and polishing to final dimension.
Five rules that save reprints
Wall Thickness
Minimum wall: 0.6 mm for solid walls, 1 mm for hollow walls.
Why: thin walls lack the structural integrity to survive UV post-cure shrinkage.
Hollowing & Drain Holes
Hollow large parts to save resin — but add ≥3 mm drain holes at the lowest points.
Why: trapped resin balloons during post-cure and can crack the shell.
Clearance for Assemblies
Allow 0.1–0.2 mm clearance between mating parts.
Why: SLA's tight tolerance still has variation; clearance prevents fused fits.
Print Orientation
Orient the part to minimise support contact on visible/cosmetic surfaces.
Why: supports leave small witness marks where they touch.
Avoid Large Flat Bases
Tilt parts 10–20° off the build plate to reduce peel forces.
Why: the suction force when peeling each layer can deform large flat bases.
How SLA stacks up
| Property | FDM | SLA | SLS | MJF | SLM |
|---|---|---|---|---|---|
| Cost | $ | $$ | $$$ | $$$ | $$$$$ |
| Surface Finish | Visible layers | Near-smooth | Slightly grainy | Slightly grainy | Rough as-printed |
| Detail | Moderate | Excellent | High | High | High |
| Tolerance | ±0.5 mm | ±0.15 mm | ±0.3 mm | ±0.2 mm | ±0.2 mm |
| Strength | Anisotropic | Near-isotropic | ~85% iso | ~95% iso | Near-isotropic |
| Speed | Fast | Medium | Medium | Fast | Slow |
| Material Range | Wide | Resins (std, tough, clear, hi-temp) | PA12, PA12GB | PA12, PA12GB, TPU | Al, SS, Ti, tool steel |
| Support-free | No | No | Yes | Yes | No |
| Best for | Prototypes & big parts | Visual & detail | Complex geometry | Production batches | Metal end-use |
Key Applications
Visual Prototypes
Presentation models for client review.
Smoothest finish convinces stakeholders.
Dental & Medical Models
Surgical guides, dental crowns, anatomical models.
High detail and biocompatible resin options.
Jewellery Master Patterns
Castable resin patterns for lost-wax casting.
Burns out cleanly with minimal ash.
Miniatures & Figurines
Tabletop game pieces, scale models.
Resolves details below 0.5 mm.
Optical Housings
Light pipes, lens prototypes, fluidic devices.
Transparent resin polishes to clarity.
Investment Casting Masters
One-off metal part patterns.
Castable resins burn out with no residue.
SLA, answered
The part comes out of the printer still slightly wet with uncured resin. The IPA wash removes it, and UV post-cure locks in the final mechanical properties — without it, the part stays soft and tacky.
Most standard resins yellow under UV light over months to years. For outdoor or sunlit use, coat with a UV-resistant clear coat or choose ASA on FDM instead.
Vertical and curved surfaces are nearly layer-line-free (Ra ~1.5 µm). Flat downward-facing surfaces show slight support touch marks but can be sanded smooth.
Yes — Transparent resin is in stock. As-printed it has a slight amber tint and a frosted surface; polishing brings it to near-optical clarity.
SLA is stiffer and more accurate but more brittle than FDM. For impact resistance, ask for Tough resin which behaves more like ABS.
Our Uniontech RSPro 1400 has a 1400×700×500 mm build envelope — one of the largest SLA machines available in Singapore.