Process analysis of ultrasonic metal welding by acoustic emission

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In recent years, ultrasonic metal welding (USMW) has proven to be a suitable technique for joining electronic components. The increasing complexity of electrical systems already prompted the industry to widely deploy this technology. However, despite its widespread application, the USMW process still suffers from quality fluctuations. The fluctuations largely originate in the lack of profound scientific knowledge and understanding of the interdependency between the tools and joining parts, which was largely ignored in past empirical studies. Recent investigations of the applicants have indicated that measurements of the changing oscillation behavior of the entire mechanical system, comprised of the tools and the adherents, can provide valuable information about the detailed state and sequence of the thermo-mechanical process within the bond interface. The (structural) acoustic emissions in particular appear to allow for a comprehensive analysis of the complex process and thus might provide a well-founded base for its description using a scientifically based model.Therefore, a fundamental investigation of the applicability of using acoustic emission as an analysis tool for the USMW process is planned in this project. For this purpose, an extensive data acquisition concept, encompassing internal and external sensor technology as well as the pre- and post-process screening of the adherents, will be developed and applied for capturing the necessary measurement data. Based on the state-of-the-art knowledge and the analysis of the acquired characteristic structure-borne and airborne acoustic emissions, the underlying physical processes will be described for the entire joining procedure.Characteristic variables which correlate with the properties of the joint, will be derived from acoustic emission and allow the prediction of the weld quality in future projects. By analysis of defined error cases on thermo-mechanical mechanism during welding a more profound understanding of the USMW process should be achieved. Once validated, the results of this project will introduce the prospective to apply on-site measurable monitoring criteria for controlling the USMW process in real-time.