Final Thesis

Vibroacoustic modelling of an ultrasonic metal welding process

Master Thesis of Uribe Corral, Jose Maria

Ultrasonic welding is a complex bonding mechanism where high frequency acoustic vibrations are applied to workpieces to reach a solid bond formation between metal plates. The workpieces, the metal objects that should be welded, are placed on top of each other on a surface called anvil, then compressed by the machine component called the sonotrode, which then starts vibrating horizontally. This leads to friction at the workpieces, between the sonotrode and anvil interfaces, which ultimately leads to the joint formation between the workpieces.
The main goal of this thesis is to study the airborne sound radiated during Ultrasonic Metal Welding. To achieve that, the structure-borne vibrations traveling from the source of vibrations to the welding tip inside the sonotrode were studied, and non-linear effects were observed [1].
In a second step, the sound radiated by those vibrations into the surrounding air was simulated. This was done with the sonotrode vibrating with no surrounding surfaces, and including some surfaces such as the anvil and other machine surfaces, from which the sound was reflected and diffracted. Both structure and air vibrations were compared to measurement data. Although the simulation results differ from the data measured, understanding the effects and physics involved during the sonotrode excitation pave the way to successfully implement a welding-quality monitoring method.