Results of an Interlaboratory Study on the Working Curve in Vat Photopolymerization II: Towards a Standardized Method

The working curve measurement in photopolymer additive manufacturing is a ubiquitous measure of the cure depth of a printing resin as a function of radiant exposure of light. The fit parameters from this measurement (the depth of light penetration D _p and the critical exposure E _c) are used to evaluate and report a resin's printability, optimize processing parameters, and inform print and resin quality control. Despite its widespread use, the working curve lacks a standard measurement method. Following up on our paper "Results of an Interlaboratory Study on the Working Curve in Vat Photopolymerization" from last year, an interlaboratory study on the working curve was performed using calibrated, reproducible, bandpass filtered light sources. With these light sources, the variability between labs in measured working curves was dramatically reduced from the initial interlaboratory study. Aggregate data from this experiment produced reliable D _p and E _c measurements at 385 nm of 39.2 ± 3.7 μm and 12.3 ± 3.0 mJ cm^-2, respectively. At 405 nm the values of D _p and E _c are 69.3 ± 3.8 μm and 17.9 ± 2.3 mJ cm^-2, respectively. The results are agnostic to the thickness measurement tool utilized by participants, ensuring broad applicability across laboratories. We also tested the generalizability of the proposed method of using a filtered light source by filtering a commercial 405 nm light source and obtaining a working curve in agreement with the aggregate data from the interlaboratory study. This interlaboratory study provides a basis for a documentary standard for the working curve, so that the entire photopolymer additive manufacturing industry can share reproducible and interoperable working curve data.