In-situ ultrasonic monitoring for Vat Photopolymerization

Abstract

Vat Photopolymerization (VPP) additive manufacturing processes employ photopolymerization reactions to crosslink monomers layer by layer under light exposure schemes corresponding to the cross-sections of a target object. Such processes have been widely used in various applications, from rapid prototyping to biomedical implants, soft robotics, and flexible electronics. In-situ process monitoring is critical for process optimization and control to achieve precise structures and desired properties via VPP. As existing research focuses on the online measurement of part geometry, there lack in-situ monitoring technologies to obtain real-time information about the curing and mechanical properties of VPP printed parts, especially the degree of conversion (DoC) that greatly affects the mechanical properties of as-printed and finished parts. This work demonstrates for the first time, an in-situ ultrasonic monitoring (IUM) method, developed based on ultrasonic testing methods for DLP process monitoring. The developed method is simplistic, rapid, versatile, cost-effective, and non-invasive compared to the state-of-the-art methods such as in-situ Fourier-Transform Infrared Spectroscopy and Atomic Force Microscopy that are adapted to monitor VPP. An IUM framework with specific data analytics methods is developed to process the real-time acquired ultrasonic signal for evaluating the evolving Young’s modulus and DoC of the as-printed part during VPP. An experimental study is performed to exemplify that the developed IUM method can vividly reveal the process dynamics under different exposure intensities and probe the part properties evolution with adequate sensitivity and accuracy. This novel IUM method will offer unique insights into process dynamics and process-property relationships for VPP processes modeling and real-time feedback control, facilitating 3D and 4D printing of sophisticated products such as soft robots that require localized manipulation of mechanical properties.