The fundamental principles of stereolithography (SLA) have been described in a limited number of key publications since the early development of the technology, including Jacob’s classic paper: Fundamentals of Stereolithography.
In practice, most production and application workflows do not require building full working curves or using detailed mathematical correlations to obtain reliable settings. 3Dresyns General Instructions for Use (IFU) provide a fast, practical, and scientifically grounded calibration approach for SLA, DLP, and LCD printers.
Core concept: cure depth control
SLA typically fabricates parts by photocuring a liquid resin layer-by-layer at a selected layer thickness. Controlling cured layer thickness (cure depth) is essential: exposure must be high enough to ensure interlayer adhesion and build success, but not so high that excessive light penetration reduces accuracy and feature definition.
Light dose can be controlled by adjusting light power (when available), scan speed (laser-based systems), or exposure time (projection-based DLP and LCD systems).
Working curve model: Cd, Dp, Ec and dose
A widely used semi-empirical model correlates cure depth to applied energy dose:
Cd = Dp × ln(E / Ec)
- Cd: cure depth (cured layer thickness), measured in µm or mm
- Dp: penetration depth at a given wavelength (depth at which irradiance is reduced to 1/e, where e = 2.718)
- Ec: critical energy (minimum dose required to reach the gel point)
- E: energy dose per area (mJ/cm2) delivered to the resin
The Cd-versus-E relationship is commonly referred to as the “working curve”. On a semi-log representation (Cd vs ln(E)), the curve becomes approximately linear: the slope corresponds to Dp, and the intercept at Cd = 0 corresponds to Ec.
This model is consistent with the exponential attenuation of light in absorbing media described by the Beer–Lambert law.
Why published Ec and Dp values often do not translate directly
Published resin parameters (including Ec) may have limited direct applicability because many printers do not disclose absolute light power, and because power readings can vary substantially depending on the light meter spectral response and calibration conditions. This is a key reason why “manufacturer values” frequently do not match the values measured on a user’s printer.
In addition, printer light power varies significantly from printer to printer and decays naturally over time, which directly impacts cure behavior and settings.
Undercure vs overcure: printability and accuracy
- Undercure (insufficient dose) can cause weak layer adhesion, incomplete polymer conversion, and print failures.
- Overcure (excessive dose) increases light penetration and can reduce dimensional accuracy and resolution by curing beyond intended boundaries.
Fine tuning approach: speed and resolution modifiers
3Dresyns Fine Tuners are designed to support predictable adjustments of cure behavior without requiring users to work with full kinetic models:
- Fine Tuners FT: photo-accelerants (photoreactivity modifiers) to increase curing speed
- Fine Tuners LB: “resolutioners” to improve dimensional accuracy and resolution by controlling light penetration
Practical calibration: curing-rate fingerprint on your printer
A simple, reproducible way to calibrate is to build a cure-thickness fingerprint for your specific printer state by curing resin drops at multiple exposure times (for example: 5, 10, 15, 20, 25, 50, 75, and 100 seconds). The resulting cured thickness-versus-time profile provides a practical basis to select exposure settings for different z-layer thicknesses.
Glass slides (around 1 mm thickness) or FEP film can be used as clear supports for curing the drops. This approach is particularly useful when printer power is unknown or changes over time.
For additional guidance: Fine tuning additives for custom tuning of printing speed, resolution, precision, and dimensional accuracy .