Ultrasonic Additive Manufacturing of Multi-Material Structures

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Ultrasonic additive manufacturing is a solid-state additive process for fabrication of fully-dense metal structures from foil stock. When combined with subtractive processes, it can be used to fabricate 3D structures that incorporate dissimilar metals (e.g., aluminum, copper, and titanium), internal conformal channels for cooling and other transport purposes, and temperature-sensitive components such as sensors, reinforcement fibers, electronic circuits, fiber optics, and smart materials. A lack of scientific understanding of the process and how it affects build properties currently limits the quality and size of builds and the range of dissimilar material combinations that can be additively welded. This award supports fundamental research in order to understand its complex process-property relationships and enable in-situ process quality monitoring using hardware that already exists in commercial equipment. Results from this research will lead to increased use of this US-based manufacturing technology in the automotive, aerospace, biomedical, and electronics industries. The research objective is to correlate macroscopic energy transfer effects (i.e., electromechanical transduction in the welder, vibrational energy imparted by sonotrode on foil, and effects of mechanical compliance on the energy available to dynamically recrystallize the microstructure) with details of the microstructure at the weld interface and mechanical properties of ultrasonic additive manufacturing builds. First-principles thermodynamic models will be formulated to describe the complete flow of energy in the ultrasonic additive manufacturing process, including system level electromechanical relationships in the welder (using classical electroacoustics theory) and quantification of the energy available to recrystallize the microstructure (from thermodynamic balances between input weld energy, surface and bulk energies, and losses). In-situ experimental techniques for measuring shear force at the sonotrode will be integrated with measurements of weld vibration amplitude, voltage, and current to validate the energy models. These validated models will be used to predict process-property relationships in new material combinations (e.g., ultra high strength steels and titanium), enable new 3D weld configurations, optimize process parameters without massive experimental trials, and provide the basis for a new power-based process control framework that overcomes current quality, size, and real-time process monitoring limitations. A key aspect of intellectual merit is that this will be the first comprehensive energy mapping of the ultrasonic additive manufacturing process and also the first to be experimentally verified by both in-situ weld power measurements and microstructural analyses.