Photopolymerization

A resin print is easy to describe in everyday language: light hits liquid, liquid becomes solid. The numerical version is less forgiving. Light has direction, wavelength, intensity, pixel geometry, and path length. Resin has initiators, absorbers, monomers, thermal coupling, and a cure state that must stay inside a physical interval.

Torrentem's photopolymerization code treats that process as a coupled model rather than a single exposure constant. DLP projectors carry rows, columns, pixel pitch, masks, and pattern intensity. SLA-style irradiators can move through a scan path. Beam profiles can be Gaussian, truncated Gaussian, or Lambertian. Beneath that surface model, Beer-Lambert attenuation converts depth and wavelength into the light that actually reaches a material point.

The Light Is Not Just A Switch

The most useful detail in the optical model is that spectrum and chemistry meet before the cure update. For broadband sources, Torrentem can reduce a spectrum to an effective kinetics wavelength weighted by photoinitiator absorption. That is a small but important distinction: a lamp's brightest wavelength is not necessarily the wavelength that drives the polymerization most strongly.

The DLP schedule path is similarly concrete. Exposure frames are built from commands, images can be preloaded, and masks become binary gates over the projected plane. The simulation therefore has a vocabulary for real manufacturing controls: pixel pitch, exposure duration, pattern intensity, and whether a point lies inside the current image.

The Cure Update

The cure variable is advanced with an implicit Euler update for a Kamal-Sourour style kinetic law. The implementation uses damped Newton steps with Armijo backtracking and a bisection fallback on the interval from zero to one. That defensive structure matters because cure state is not an arbitrary scalar. Once it escapes the physical interval, the rest of the material model becomes unreliable.

Torrentem also leaves room for temperature-sensitive rates. Activation energies, reference temperatures, gas constants, and resin-specific overrides can all affect the reaction constants. The result is a model that can start as isothermal optics and grow toward a coupled heat-and-cure simulation without changing the vocabulary of the page.

What makes the module interesting is not only the number of resin types or LED traits. It is the decision to keep optical geometry, spectral absorption, and nonlinear kinetics in the same modelling frame. That is what turns a pretty cure-depth plot into a simulation of a manufacturing process.