Prozessanalyse der thermo-mechanischen Vorgänge während der Verbindungsbildung beim Metall-Ultraschallschweißen

Ultrasonic Metal Welding (USMW) is a particularly suitable process for joining electric components and its use is growing due to the increasing complexity of electronic systems. Despite its widespread application, USMW suffers from quality variations. These are often unclear due to a lack of deep scientific knowledge regarding the complex interactions between tools and joining parts during welding process. Therefore, the aim of this doctoral thesis is to describe thermo-mechanical processes in the mechanical overall-system, consisting of horn, anvil and joining parts, which occur during bonding formation in USMW of similar sheet metal joints of copper. This work is divided in three main parts: Chapters 4 and 5 present the experimental setup with process data acquisition system, the processing of the measured signals and an evaluation concerning their suitability for process analysis. For this purpose, in addition to the machine internal sensors, the oscillation behavior of the mechanical overall-system during the USMW process is recorded externally by a high-speed camera and two laser Doppler vibrometers. The processed measurement signals are used in chapter 6 to identify characteristic transient process signals. In order to be able to assign concrete states of bonding formation to these signals later on, the welding process is stopped after defined times and the bonding formation is characterized under microstructural and fracture-mechanical aspects. Finally, in Chapter 7, the thermo-mechanical processes taking place during bonding formation are described by a process phase model by correlating characteristic process signals with the mechanisms of bond formation. The final verification under changed process conditions also provides information about the interchangeability of the model. Regarding the current state of research, the results of the present work allow deeper insight into the thermo-mechanical processes taking place in USMW. Thus, the in-situ process analysis is helpful to a more profound understanding and leads to an improved process capability of the USMW

Effects of heat treatment and welding process on superelastic behaviour and microstructure of micro electron beam welded NiTi

Medical devices with small dimensions made of superelastic NiTi become more popular, but joining these parts remains challenging. Since laser welding was found to be an option, electron beam welding seems to be an interesting alternative as it provides additional advantages due to the precise beam positioning and the high vacuum. Superelasticity is influenced by microstructure and surface layer composition that are mainly affected by welding process and by heat treatment and therefore will be investigated in the present paper