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Purpose: Ultrasonic additive manufacturing (UAM) is a fabrication technology based on ultrasonic metal welding. As a solid-state process, temperatures during UAM fabrication reach a fraction of the melting temperatures of the participating metals. UAM parts can become mechanically compliant during fabrication, which negatively influences the ability of the welder to produce consistent welds. This study aims to evaluate the effect of weld power on weld quality throughout a UAM build, and develop a new power-compensation approach to achieve homogeneous weld quality.

Design/methodology/approach: The study utilizes mechanical push-pin testing as a metric of delamination resistance, as well as focused ion beam and scanning electron microscopy to analyze the interface microstructure of UAM parts.

Findings: Weld power was found to negatively affect mechanical properties and microstructure. By keeping weld power constant, the delamination energy of UAM coupons was increased 22 per cent along with a consistent grain structure. As a result, to ensure constant properties throughout UAM component construction, maintaining weld power is preferable over the conventional strategy based on amplitude control.

Research limitations/implications: Further characterization could be conducted to evaluate the power control strategy on other material combinations, though this study strongly suggests that the proposed approach should work regardless of the metals being welded.

Practical implications: The proposed power control strategy can be implemented by monitoring and controlling the electrical power supplied to the welder. As such, no additional hardware is required, making the approach both useful and straightforward to implement.

Originality/value: This research paper is the first to recognize and address the negative effect of build compliance on weld power input in UAM. This is also the first paper to correlate measured weld power with the microstructure and mechanical properties of UAM parts.

A. HEHR, P.J. WOLCOTT, and M.J. Dapino, “Effect of weld power and build compliance on ultrasonic consolidation,” Rapid Prototyping Journal, 22 (2), 377-386, 2016.

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This paper focuses on the development of a 3D hysteretic Galfenol model which is implemented using the finite element method (FEM) in COMSOL Multiphysics®. The model describes Galfenol responses and those of passive components including flux return path, coils and surrounding air. A key contribution of this work is that it lifts the limitations of symmetric geometry utilized in the previous literature and demonstrates the implementation of the approach for more complex systems than before. Unlike anhysteretic FEM models, the proposed model can describe minor loops which are essential for both Galfenol sensor and actuator design. A group of stress versus flux density loops for different bias currents is used to verify the accuracy of the model in the quasi-static regime. Through incorporating C code with MATLAB, the computational efficiency is improved by 78% relative to previous work

Z. DENG and M.J. Dapino, “Characterization and finite element modeling of Galfenol minor flux density loops,” Journal of Intelligent Material Systems and Structures, Vol. 26, pp. 47-55, January 2015.