ANALYZING BLENDED MATERIAL TRANSITIONS PRODUCED BY A DUAL-HOPPER LARGE FORMAT ADDITIVE MANUFACTURING SYSTEM

Additive Manufacturing (AM) has seen rapid growth in terms of popularity, capabilities, and methods in recent years, especially in multiple material (MM) printing vital to expanding the applications of AM beyond modelling and prototyping. While small-scale systems have successfully demonstrated MM printing capabilities, Large-Format Additive Manufacturing (LFAM) instruments have remained largely limited to single-material processing. This dissertation investigates a novel method for MM LFAM printing utilizing a novel dual-hopper configuration developed for the Big Area Additive Manufacturing (BAAM) system from Cincinnati Inc. The BAAM dual hopper produces blended material transitions in-situ by switching from one material to the next. The primary goal was to characterize the material transition process through analysis of processing parameter effects on transition rate, transition length, and mechanical properties. Initial work investigated compositional analysis methods and developed a novel technique for analyzing reinforcement content. A novel framework for comparing transitions printed with different conditions was developed through normalizing by a system-specific residual volume. Multiple material transitions were printed using different screw speeds and system configurations for both an acrylonitrile butadiene styrene (ABS) and carbon fiber-reinforced ABS (CFASB) material pair and a CFABS and thermoplastic polyurethane (TPU) material pair. The analysis framework indicated that screw speed had negligible influence, but transition direction, screw design, nozzle design, and material viscosity demonstrated significant relationships with transition behavior. A mathematical model was developed and verified these observations. This suggested the transition process could incorporate site-specific properties into printed LFAM structures. Complementary investigations characterized the internal morphology, cross-sectional homogeneity, and inter-bead strength of printed structures as a function of fiber content. The dual-hopper system demonstrated effective in-situ material switching that avoids discrete material boundaries typically found in MM-capable systems.