Final Thesis

Process state estimation in Ultrasonic Metal Welding from airborne sound recordings

Key Info

Basic Information

Research Area:
Numerical Acoustics,
Type of Thesis:


Bachelor Thesis of Ercandogu, Eylül

Ultrasonic metal welding is a solid-state bonding process in which metal workpieces are exposed to high-frequency vibrations. It is an effective joining technology with a wide range of industrial applications with its unique advantages. The vibrations of mechanical parts in the machine cause fluctuations in the air pressure, thus causing sound waves to radiate. The radiating sound may be directly related to the component vibrations. As a result, changes in the process can be monitored by detecting changes in the airborne sound. This thesis aims to study the airborne sound radiated during ultrasonic metal welding and estimate the relation between the sound and the process stages. Several features are examined to achieve this goal, starting with frequency analysis. The spectrogram of the airborne sound shows that the sound emitted has a mostly constant amplitude and contains many frequencies, most notably the fundamental frequency and its harmonics. These frequencies are examined in relation to time in order to define transitions between different stages. Additionally, a relationship between the welding strength and the welding frequency is investigated but no correlation was discovered. Two ratios are derived to measure nonlinearity, one comparing the fundamental frequency with all other frequencies, and the other with its harmonics. The analysis presents comprehensive tables showing the relationship between welding stages and the studied features. It is evident from the tables that there is a correlation between the frequency behaviors and the stages of the process.