CAREER: Viscosity-tunable Photopolymers with Metal Powder Mixtures for Cost-effective, High-speed and Large-area Metal Additive Manufacturing

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Modern metal additive manufacturing (AM) mostly relies on a point-by-point printing scheme, in which the fabrication time increases substantially with the size of a part, in particular, the cross-sectional area of the part. Such a processing constraint prevents metal AM from being a viable alternative for large-scale production of parts in transportation, construction and many other applications. To overcome the challenge, this Faculty Early Career Development (CAREER) award supports fundamental research for an untested metal AM process, whereby a whole layer is first printed at once by curing a mixture of photopolymer and metal powder using digital light projection, followed by debinding and sintering, resulting in high-speed production. The new process hinges on a unique photopolymer with tunable properties, to balance the print-layer curing depth and homogeneous mixing of metal powder in a photopolymer suspension. If successful, this metal AM system, first of its kind, will be beneficial to heavy industries such as transportation, machinery and construction, and provide a competitive edge to U.S. industries in the global market. The project team will also organize webinars and workshops tailored for engineers to learn how the new metal AM system can be incorporated into practices, as well as introduce basic AM principles to K-12 students, offering hands-on activities (i.e., LEGO 3D printing) to inspire their interest in STEM professions.The overall goal of this research is to understand the process mechanism of a metal AM system that utilizes photopolymerization of a photopolymer and metal-powder mixture based on light projection rather than scanning, with emphases on challenges in metal powder sedimentation, curing capacity and possible oxidation-related defects. The project will first investigate the combination of thermoset-thermoplastic polymers to comprehend and control the viscosity of photopolymers. Numerical models of curability and powder packing will then be utilized to characterize the curing depth and the packing density as a function of particle size distributions in a photopolymer-powder mixture. Thermal gravimetric and microstructural analyses will also be employed to study debinding and sintering behaviors of photopolymer-powder mixtures. Moreover, a solid-state sintering model will be developed to evaluate the final part quality. The research findings will reveal principles that influence the rheological properties as well as behaviors during the curing, debinding, and sintering of photopolymer-powder mixtures. The new AM approach has the potential to allow fabrication of fully-dense, complex, and large metal parts at a high speed without oxidation or deformation. The new knowledge obtained is expected to also support advances in other AM processes, such as binder-jet 3D printing of ceramics, to improve the fabrication speed as well as the part quality.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.