SLA
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Stereolithography
SLA & MSLA

UV light cures liquid photopolymer resin layer by layer — delivering extraordinary surface resolution and smooth finishes that FDM cannot approach.

Precision through light

SLA uses a UV laser to trace each layer in a vat of liquid resin. MSLA uses an LCD screen to flash entire layers simultaneously — dramatically improving speed while maintaining resolution. DLP uses a digital projector as the light engine.

Modern 12K mono LCD MSLA printers achieve XY resolution of 19µm — smaller than a human blood cell — at desktop price points under ₹30,000.

Advantages

  • Exceptional surface finish (Ra < 2µm) straight from the printer
  • Fine feature resolution — details under 100µm achievable
  • Dental and medical-grade biocompatible resins available
  • Castable formulations for direct jewelry investment casting
  • MSLA and DLP far faster than laser SLA for large layer areas

Limitations

  • Support structures required — tricky to remove from delicate features
  • Mandatory post-processing: wash + UV cure station needed
  • Uncured resin is toxic — PPE and ventilation non-negotiable
  • Standard resins are brittle vs. FDM engineering filaments
  • Build volumes limited compared to FDM at equivalent price

SLA / MSLA Specifications

Layer Height10–100µm
XY Resolution19–50µm (MSLA)
Build VolumeUp to 292×165×400mm
MaterialsPhotopolymer resins
Post-processWash + UV cure
Tolerances±0.1mm typical
Surface FinishRa ~2µm
Best ForJewelry, dental, prototypes
Fundamentals
SLA Basics

Understand photopolymerization, light engines, resin chemistry, and the complete SLA workflow from start to cured part.

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Light Engines: SLA vs MSLA vs DLP
SLA uses a single UV laser scanning the layer — slow but extremely precise. MSLA uses an LCD screen masking a UV LED array — cures entire layers at once. DLP uses a digital projector — highest single-point intensity, suited for engineering resins requiring short cure times.
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Resin Chemistry — Basics
Resins contain photoinitiators that fragment under UV light, triggering free-radical polymerization of acrylate monomers. The result is a crosslinked polymer network. Resin properties depend on oligomer and monomer ratios in the formulation.
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Build Orientation & Supports
Parts print inverted in MSLA/DLP — the build plate lifts up through the vat. Each layer peels from the FEP film. Support structures anchor the part to the plate and prevent failure during peel.
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Post-Processing Workflow
After printing: (1) Drain excess resin into vat. (2) IPA or water-wash bath for 2–5 minutes. (3) Post-cure under UV lamp (405nm) for 1–3 minutes per side to complete polymerization.
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Safety Essentials
Uncured photopolymer resin is a skin sensitiser. Always wear nitrile gloves, safety glasses, and ensure adequate ventilation. Dispose of resin-contaminated IPA by UV curing it solid before bin disposal.
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Key Print Settings
Normal exposure time: 1.5–4 seconds/layer. Bottom exposure (first 6–10 layers): 30–60 seconds for adhesion. Lift speed and distance controls peel force on FEP. Anti-aliasing blends layer pixel edges for smoother curved surfaces.
Step 01
Orient & Support
Position model to minimise peel forces and support contact on critical surfaces.
Step 02
Slice
Configure exposure times, lift speed, and layer height in Chitubox or Lychee Slicer.
Step 03
Print
Load resin, level plate. Print time: 30 min–12 hours. Monitor FEP for clouding.
Step 04
Wash
IPA or water wash 2–5 min. Rinse and shake to remove resin from cavities.
Step 05
Cure & Finish
UV cure station 1–3 min. Remove supports, sand, prime and paint as required.
Deep Engineering
SLA Engineering

Cure depth physics: Beer-Lambert law governs UV penetration in resin. Cure depth C_d = D_p × ln(E_max / E_c) where D_p is the penetration depth constant of the resin, E_max is the peak irradiance, and E_c is the critical energy threshold for gelation. Controlling E_max through exposure time directly controls cure depth and achieves Z-resolution.

19µm
XY Resolution
12K MSLA
Photopolymerization Kinetics

Free-radical polymerization proceeds in three stages: initiation (PI fragments under UV), propagation (chain growth), and termination (chain coupling or oxygen inhibition). Oxygen inhibits surface cure — hence tacky surfaces on under-exposed parts.

C_d = D_p · ln(E_max / E_c)
D_p = resin sensitivity (mm), E_c = critical energy (mJ/cm²)
Typical: D_p = 0.1–0.2mm | E_c = 10–25 mJ/cm²
  • Over-exposure causes blooming — XY expansion beyond pixel boundaries
  • Under-exposure causes layer delamination and poor inter-layer adhesion
  • FEP film oxygen-inhibition layer contributes 5–15µm uncured resin to each layer
  • nFEP and ACF film reduce peel forces by 40–60% vs standard FEP
Resin Formulation Engineering
  • ABS-Like resins: Core-shell rubber toughening particles — improves Charpy impact 2–4× vs standard
  • High-Temp resins: DCPD monomers raise HDT to 220–280°C — suitable for tooling and under-hood automotive
  • Dental / Biocompatible: ISO 10993 certified — restricted monomer list for intraoral contact safety
  • Castable Wax resin: ≤0.01% ash at 500°C burn-out — critical for zero contamination in precious metal casting
  • Flexible TPU resins: Shore 30A–80A range — elongation to break 100–200%, fatigue-resistant hinges
Dimensional Accuracy & Calibration
FactorEffectCompensation
Pixel Blooming+0.05–0.15mm XYHorizontal size compensation in slicer
Resin Shrinkage0.5–2.0%Scale factor in slicer per resin profile
Bottom Layers Squish+0.05–0.1mm ZReduce bottom exposure, raise lift height
Support Witness MarksSurface Ra spikeReduce contact diameter to 0.3–0.5mm
DfAM for Vat Photopolymerization
  • Hollow parts: add drainage holes ≥3mm diameter to allow resin evacuation — trapped resin causes print failures
  • Wall thickness minimum: 0.5mm for MSLA, 1.0mm for laser SLA
  • Orient critical surfaces facing upward (away from FEP) for best Ra
  • Suction cup effect: large flat horizontal surfaces trap resin — add vacuum relief holes
  • 45° orientation rule: angle large flat faces to reduce layer peel area
  • Dental splints, hearing aids, and jewelry patterns routinely achieve ±0.1mm tolerances
Advanced Post-Curing Science

Parts from the printer are only ~50–70% converted. Post-curing completes polymerization and maximises mechanical properties. Excessive curing causes embrittlement through over-crosslinking.

  • Optimal cure: 405nm wavelength matches most commercial resin PI absorption peaks
  • Temperature-assisted cure (60°C) significantly speeds conversion rate
  • Underwater UV curing eliminates oxygen inhibition, producing higher surface hardness
  • Monitor cure completion via FTIR spectroscopy — peak reduction at 810 cm⁻¹ (acrylate C=C)
SLA vs MSLA vs DLP Comparison
AttributeSLA LaserMSLA LCDDLP Projector
XY Resolution~50–100µm19–50µm25–75µm
Layer Cure TimeVariable (scan)1–4 sec0.5–3 sec
UniformityExcellentGood (LCD wear)Excellent
CostHighLow–MediumMedium–High
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