Ultrasonic Additive Manufacturing (UAM) is a novel rapid manufacturing process that is  both additive/ subtractive;  combining ultrasonic welding with  computer numerical control (CNC) milling.  UAM permits bonding metals at half their melting temperature and allows the development of metal matrix composites along with the embedding of smart materials, actuators and sensors seamlessly in metal. However, the process suffers from a critical limitation, i.e.,  a range of build heights within which bonding between a new foil and the build feature cannot be originated. Previous, dynamic models of the UAM process  have been used to show that  as the height of the feature increases its first modal frequency approaches the excitation frequency of the sonotrode coincides with lack of bonding. Researchers theorize that this is due to the workpiece effectively sticking to the sonotrode causing a decrease in the frictional stresses in the bonding region. However,  all research work to date has been incomplete: 1) research effort have neglected the effects of  higher-order modes on the dynamic response and, 2)  do not simulate the entire weld cycle when studying the dynamics near critical height-to-width ratios. In this manuscript, a model consisting of a parallelepiped under a multidirectional moving load was developed to study the dynamic response of the build feature near critical build heights for nominal tape width build features. Again, based on the hypothesis that the cause for the critical height-to-width ratio is dynamic interaction between the substrate and top foil/sonotrode the current model predicts a maxima in the velocity response in the transverse direction directly underneath the moving load (simulated sonotrode excitation) as the build height is increased. This observation is validated by experimental results. Furthermore, the current model predicts that as the height is further increased, a maximum in the velocity response in the transverse direction directly underneath the moving load occurs at a height-to-width ratio of 1.2. This is caused by interactions between the applied excitation force and higher-order modes. This indicates that a single mode-approximation is not sufficient to describe the dynamics near critical build heights. Further increases in build height have lower magnitude velocity responded  but local maximums are still present near a height-to-width ratio of approximately 2.6. The results correlate with experimental evidence that bonding can be reinitiated in high aspect ratio features.  Finally, in studying the time response for an entire weld cycle (1.5s), the amplitude of the velocity response in the transverse direction varies on near an order of magnitude between the start of the weld cycle and the middle of the weld cycle. This indicates that assuming a quasi-static or analyzing a short time period in a model excludes potential dynamics during an entire weld cycle (on the order of 1s).


Dynamic Response Near Critical Build Heights in Ultrasonic Additive Manufacturing

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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