Development and validation of a method to determine the frequency- and temperature-dependent stiffness and damping properties of plastics for the structure-borne noise simulation more precisely using the example of the for the ultrasonic welding process relevant frequency of 20 kHz

• Applicant: Professor Dr.-Ing. Christian Hopmann
• Subject Area: Plastics Engineering
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398244070

The ultrasonic welding has been established in the industry since the 1960s. Up to now, the design of the joining parts is usually based on the user experience. As well as the geometric design of the joining part bodies, which has to be suitable for welding, an appropriate component construction requires the consideration of constructive details, such as a process-specific design of the joining zone geometry. Additional functional elements or rib structures, which directly affect the structure-borne sound processes and thus the welding process, are often also to be taken into account. In general, extensive practical trials are necessary before the start of production.The component development also requires extensive practical trials for the determination of the welding parameters. In many cases, iterative elaborate and cost-intensive redesigns of the injection moulding tools arise to influence the sound propagation, so that a high-quality weld seam is achieved. The material analysis of the dynamic stiffness and damping behaviour of plastics is challenging due to the high frequencies of ultrasonic welding, and can only be carried out by means of iterative approaches. Realistic simulation of the acoustic structure interactions can be contributed to detect and avoid critical areas. However, input data are required, which precisely reflect the viscoelastic material behaviour of thermoplastic plastics.The aim of the research project is a further development of an alternative method, which is based on a reverse engineering process. This is supposed to determine mechanical characteristic values for an amorphous plastic (PMMA) and two semi-crystalline plastics (PP and PA), which allow a model description of the complex structure-borne sound processes in joining parts for the ultrasonic welding process, taking into account thermal influences.With the help of the research results, it is to be shown that the appropriate joining part design can already take place in the design phase. As a result, time and cost-intensive iterations in the development phase of complex joining parts will be omitted. Furthermore, a comprehensive basis for a better material and process understanding of the highly dynamic ultrasonic welding process and the sound propagation will be created.

• DFG Programme: Research Grants