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SEP 2018

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NEWS 53 CompositesWorld.com adapt to PEKK, PAEK and PEI," he adds. "We should be able to weld unidirectional (UD) tape as well," he also notes (challenges associated with welding UD tapes are explained below). Kupke says there is no limit to the part thickness being welded, "it could be 3 mm or 30 mm, but care must be taken with thermal manage- ment at the weldline." He says the next step will be to develop a range of optimized CF resistive elements. "We've just used off-the-shelf materials for now." Kupke points outs this was only a demonstrator, not an indus- trial process. "To industrialize, we would do it a bit differently. e welding process for each join in the A320 bulkhead took 4 minutes, however, only 90 seconds of welding current was applied. e remaining time was for heating and cooling of the PPS thermoplastic at the weldline. With industrialization, we believe the total time would be faster and the welding would still take only 60-90 seconds per 1.5m join." Induction welding KVE began working with induction welding in the early 2000s. e basic tech- nique involves moving an induction coil along the weldline. e coil induces eddy currents in the inherently conductive CFRP laminate, which generate heat and melt the thermoplastic. "We began with single-lap shear coupons, following the building block approach, and progressed to L-joints, T-joints, then basic struc- tures and finally elevators and rudders," recalls KVE managing director Harm van Engelen. e company developed computer simulations in parallel. "Simulation helps you to predict what the tempera- ture will be at the outer surface and at the weldline," he explains. "You need to concentrate heat in the weldline, but not overheat adjoining sections. e top surface heats up faster than the inter- face, so you have to get rid of that heat." KVE patented not only the resulting heat management technology, but also its tooling-based approach to main- taining pressure during welding, and its robotic control of the induction coil and weldhead, which it developed by 2005. "is provided an alternative to resis- tance welding for CFRP that did not require a susceptor or welding strip," says GKN Fokker's Offringa. "We licensed the KVE technology and implemented it on the Gulfstream G650 elevators and rudder, which have been flying since 2008." KVE was a key partner in the development and indus- trialization of the robotic induction welding process. A refined second-generation technique is used for the elevators and rudder on the Dassault Falcon 5X. Van Engelen notes that welding for the G650 was automated but completed in multiple steps. "For the Dassault, it is done in one shot," he adds. "All of the parts are placed in the tools and then two elevators and a rudder are welded in one shift overnight." By 2008, KVE had begun single-lap shear (SLS) testing of Welding Thermoplastics

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