C. Gonzalez Lugo, K. Fouladi, B. Eslami
Keywords: additive manufacturing, 3D printing, relative humidity, computational fluid dynamics
Summary:Common additive manufacturing (AM) filament materials such as polylactic acid (PLA) are hygroscopic causing the polymer to attract and absorb moisture from the surrounding environment. It is shown that relative humidity (RH) can adversely affect the material properties (e..g., strength) of filament materials like PLA. A controlled enclosure would be ideal to reduce the negative effects of RH on the final quality of 3D printed parts. This project is focused on designing and developing an environmentally controlled enclosure for a commercial 3D printer. Numerical simulation using computational fluid dynamics (CFD) and experimental testing were both utilized to investigate various designs for the environmentally controlled enclosure. CFD simulations can provide the necessary information to select the optimal and feasible design while experimental testing is used to validate the CFD simulation results. The environmentally controlled encloser allows for test samples to be printed at several RH percentages (20% RH, 50% RH, 80% RH). The test samples were characterized at both macro- and micro-scale. The macro-scale characterization was performed by static tensile testing procedure, while the micro-scale polymer material properties were done using Atomic Force Microscopy (AFM). Overall, an environmentally controlled enclosure was designed and developed with an average RH uniformity of over 0.70. The enclosure is able to print three batches of ASTM D638 standard test samples at 20% RH (Low RH), 50% RH (Mid RH), and 80% RH (High RH). Through the macro-scale characterization, it was shown the samples printed at lower humidity had statistically significantly higher tangent modulus, ultimate tensile strength, and rupture strength. These studies were also verified by AFM studies at micro- and nano-scale. In this study, it was found printing PLA at lower humidity can enhance the effective printed parts quality. To achieve this capability, an environmentally controlled enclosure was designed and developed.