Development of durable sonotrode concepts for ultrasonic welding of Ti alloys by designing an efficient structuring of the sonotrode tip

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Ultrasonic welding processes are inexpensive and environmentally friendly joining methods to cre-ate robust joints of similar or dissimilar materials within fractions of a second. The welding tools used in this process, known as sonotrodes, cause the formation of the bond by oscillation in contact with the upper joining partner and are therefore exposed to high thermal and mechanical stresses, which in continuous use result in a relatively short longevity of only a few days. Recently, sono-trodes where developed especially for ultrasonic welding of titanium alloys by the applicants, whose wear behavior depends not only on the sonotrode material but also significantly on the structuring of the sonotrodes. In this research project, the influence of the sonotrode structuring on the quality of Ti/Al joints and the longevity of the sonotrodes will be systematically investigated. Finite element simulations are used to calculate stresses and deformations of sonotrodes with differently structured tips and the joining partners in a first step, without having to manufacture the sonotrodes. In order to validate the calculations, sonotrodes with the most promising structuring will be manufactured and welding experiments will be performed considering the achievable strengths and the resulting microstruc-ture in the joining area. Parallel to the welding experiments, the sonotrode wear is documented and characterised. The analysis of the microstructure in the joining area in combination with the resulting joint strengths and the wear behaviour will support the design of optimised sonotrode structures to increase joint strengths, extend tool life and broaden the basic understanding of ultrasonic welding sonotrodes.