Smart ultrasonic welding of thermoplastic composites

This paper presents an overview of the latest research on ultrasonic welding of composites performed at the Delft University of Technology. Firstly, we showed that for thermoplastic composites, a simple flat energy director shape, made of a loose film of neat resin, can be used to produce welds of high quality. Furthermore, for single lap shear coupons, it was shown that the use of a microprocessor-controlled welder allows for in-situ monitoring through power and sonotrode displacement data. As a result, a smart ultrasonic welding procedure was designed in which the feedback from the ultrasonic welder was used to define the processing parameters that yield optimum weld quality, significantly decreasing development times. Based on the knowledge developed at a lab-scale level, a welding strategy was developed to demonstrate the assembly of small and medium-sized components. Experimental comparison between ultrasonically spot-welded and mechanically fastened joints into double-lap shear and pull-through configurations further outlined the potential application of this technology, as well as its limitations. While ultrasonic welding is an efficient technique to join thermoplastic composites components, another potential application was shown to be the welding of thermoplastic and thermoset composites, enabled through the very short heating times in the ultrasonic welding process. This opens up new possibilities for ultrasonic welding where optimum design and manufacturing of aircraft parts call for the assembly of dissimilar materials, and could lead to significant costs and weight reduction as compared to mechanical fastening.