Multi-material joints are a key element for the application of lightweight construction in the transport sector. Our member Institute of Polymer Engineering at FHNW, together with MultiMaterial-Welding GmbH, has now brought a new joining technology to industrial maturity.

MultiMaterial-Welding GmbH has developed and patented an innovative platform of various products and solutions that offers a new method for joining different materials. One of these is the MM-Welding® LiteWWeight® technology, which is specially designed for sandwich structures with honeycomb and foamed core materials. Ultrasonic energy is used to introduce a thermoplastic fastener through the face sheet into the porous structure of the core. Due to the ultrasonic excitation, the thermoplastic connecting element partially melts at the interface, infiltrates the porous structure and establishes a highly stressable frictional and positive connection with the substrate.

Addressing the mechanical behaviour is the key to success. Therefore, experimental and numerical methods were jointly developed during the project to better understand the dynamic and fast process and to be able to use it industrially.
By means of an online process monitoring system, which was specifically developed for this technology, the relationship between mechanical load capacity and process parameters could be better understood through the acquisition and evaluation of high-resolution process data. In addition, a high-speed camera was used to obtain information about the penetration behaviour, such as buckling of the thermoplastic fastener under pressure, during the very short process. Furthermore, it was important to investigate the vibration behaviour of the thermoplastic fastener in more detail. By means of numerical analyses of the frequency behaviour and the elastic wave propagation, the geometry and process could be optimised and thus stabilised. This project illustrates the high increase in knowledge through the coupling of experimental and numerical methods. (Report FHNW)
The complete report can be found on the FHNW website.