Light Becomes Solid
Stereolithography converts liquid resin into solid plastic using the energy of ultraviolet light. When a UV photon strikes a photoinitiator molecule dissolved in the resin, it generates a free radical that triggers a chain reaction of monomer crosslinking. Within milliseconds, a liquid drop transforms into a rigid polymer network. By precisely controlling where light strikes, SLA builds objects with resolution measured in tens of micrometers — the finest of any 3D printing technology.
The Jacobs Equation
The cure depth Cd = Dp × ln(E/Ec) is the master equation of SLA. It states that polymerization depth depends logarithmically on the ratio of delivered energy E to the critical threshold Ec, scaled by the resin's optical penetration depth Dp. This logarithmic relationship means doubling the laser power does not double the cure depth — it adds only one Dp of additional penetration, a crucial insight for process optimization.
Balancing Cure and Overcure
Every SLA layer must cure slightly deeper than the layer thickness to bond with the previously cured layer below. This deliberate overcure — typically 20-50 μm — ensures structural integrity. But excessive overcure causes overhanging features to thicken, distorting dimensional accuracy. The simulator lets you tune exposure to find the sweet spot: enough overcure for adhesion, not so much that geometry suffers.
Resin Chemistry Matters
The penetration depth Dp and critical exposure Ec are resin properties, not machine settings. Clear resins have large Dp (deep penetration, risk of overcure), while pigmented or filled resins have small Dp (shallow cure, need for higher exposure). Photoinitiator concentration, monomer reactivity, and UV absorber additives all interact to define the working curve. The simulator abstracts these into Dp and Ec, letting you explore how resin chemistry governs the SLA process window.