SEP 2018


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NEWS 59 Gulfstream aircraft, "We have used ultrasonic welding for joining more than 50,000 injection molded TPC parts to floor panels. It is very fast and highly automated, but it's a spot weld, at only one location." Still, he sees potential for this method in produc- tion of an integrated fuselage, like that proposed in the Clean Sky 2 program's Multifunctional Fuselage Demonstrator (see Learn More, p. 63). "Fuselage brackets are often bonded, riveted or bolted to current thermoset composite fuselage structures," Offringa observes. "With ultrasonic welding, you can achieve very good connection with brackets, which are often unreinforced thermoplastic." Ultrasonic welding has been used with plastics for several decades, typically with energy directors at the weld interface. ese triangular or rectan- gular ridges of neat resin, molded into the surfaces to be welded, increase local heat generation. However, Irene Fernandez Villegas at Delft University of Technology (TU Delft, Delft, e Nether- lands) has shown that 0.08-mm thick, unreinforced thermo- plastic films may be used in their place. "She is working to develop continuous ultrasonic welding," says Offringa, and this work is continuing within Clean Sky 2. In her 2016 paper, titled "Smart ultrasonic welding of thermo- plastic composites," Villegas states that it is possible to scale up the ultrasonic welding process via sequential welding — that is, letting a continuous line of adjacent spot welds serve the same purpose as a continuous weld bead. Lab-scale sequential spot welding was used in the Clean Sky EcoDesign demonstrator's TPC airframe panel, using flat energy directors to weld a CF/PEEK hinge and CF/PEKK clips to CF/PEEK C-frames (Fig. 6, p. 60). Experimental comparisons with mechanically fastened joints in double-lap shear and pull-through tests showed promise. e process is further explored in 2018 papers by Villegas' TU Delft team member Tian Zhao. Kupke reports that DLR ZLP also is working on robot-based continuous ultra- sonic welding. "Spot welding is the current state of the art, but ours is truly continuous," he says. "We are optimizing the process on a roughly 1m-long test bench, performing parametric studies using different materials and configurations. ough the welding machine and digital control are designed for a robot manipulator, we are still exploring how to refine the head and which velocity and energy works best for each material and laminate thickness. Our objective is to show you could do very long welding, such as the joints of a fuselage." Laser welding Although laser transmission welding was discussed in Yousef- pour's 2004 review of TPC welding technologies, it has since The greatest driver for TPC use in aircraft is the ability to join components via fusion bonding/welding. Welding Thermoplastics

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