Analysis of the linearity limitations of Jacobs working curve for stereolithography (SLA) additive manufacturing and exploration of potential alternatives through scaling analysis

Photopolymerization-based Additive Manufacturing (PAM) has grown in the last few years due to its capability to create parts that have complex geometries that are difficult or impossible to produce with non-additive methods. However, PAM requires a harmonious control of chemical reaction kinetics, mechanical actuation, and optical instrumentation to achieve optimum results. Therefore, a framework that connects these systems is crucial to understand how to match the chemistry of a resin to the mechanical and optical parameters of the printer. To date, the only available theoretical framework to achieve this is the so-called Jacobs Working Curve (WC). The Jacobs WC explains the connection between key printing parameters that must be properly set as a function of every resin, for example the penetration depth (Dp) and the critical dose (Ec) as a function of the cure depth (Cd), writing speed, linewidth, etc. The problem is that the Jacobs Working Curve is affected by a significant used-dependent variability and that alleged linearity stems from an oversimplification of the polymerization-based printing process. Notably, no standardized method to perform a working curve measurement has been done. Therefore, Dp and Cd values can vary by several factors and magnitudes from on user to another. Furthermore, even amongst data from a single user, a linear dependence between the incident radiant exposure (E0) and the Cd is seldom obtained. On the contrary, it is more common to obtain multiple linear regimes and uncertainty about whether absolute Dp and Cd values could be estimated from this method. In this work, we discuss a potential route to capture the inherent non-linearity of VAT photopolymerization using scaling analysis and dimensionless numbers along with a comprehensive characterization of the reaction kinetics of several SLA resins. We employed a coupled UV-Vis and NIR customed-built set-up to obtain the required kinetic data for the polymerization of commercial and in-house resins to establish correlations to the results that one would obtain with the standard Jacobs equation as compared to the analysis through adapted dimensionless numbers for the prediction of the critical dose.

https://orcid.org/0000-0003-0455-5401

56168092600