Transfer path analysis for vibro-acoustic quality monitoring for ultrasonic metal welding
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Bachelor Thesis of Joyeux-Alcindor, Thomas
Ultrasonic Metal Welding (USMW) is a technique used for numerous industrial applications. However, the welding process is in fact poorly known, and same values of input machine parameters can lead to different weld qualities. It is necessary to assess with more details which phenomena happen during welding, to extend the use of USMW. This thesis aims at caracterizing the transfer of vibrations, called the transfer path, between two pieces of the USMW machine, the horn and the anvil. To do so, measurements have been done using laser vibrometers. With an input, the horn displacement, and an output, the anvil displacement, it is possible to identify a system representation tool called a transfer function, which describes the transfer path. Matlab has got indeed various identification algorithms to compute a mathematical link between an input signal and an output signal. After a study of the literature and of the mechanical models, a transfer function order will be derived, and used for the identification. This work has shown that the transfer function order derived fits well with the measurement signals. The mechanical model used for this thesis can be considered as representative of the welding system. Also, the transfer function identified on the startup of the welding has indicated poor performances compared to the rest of the welding signals. It has been assessed that the beginning of the welding can hardly be considered as a linear system. Keywords : Ultrasonic Metal Welding (USMW), transfer function, identification.