SEP 2018


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NEWS 51 Welding Thermoplastics of ermoplastic Composites," by Ali Yousefpour, National Research Council Canada (Ottawa, ON, Canada), "e process of fusion-bonding involves heating and melting the polymer on the bond surfaces of the components and then pressing these surfaces together for polymer solidification and consolidation." e result is very different from thermoset joining. "You are creating a unitized structure, such as a rib welded to a skin," explains Arnt Offringa, head of Aerostructures R&T for GKN Fokker (Hoogeveen, e Netherlands). "When viewed under a microscope, you see just homogeneous polymer, so this is different than bonding. ere is no dividing line, no split, no identifiable joining material such as adhesive. ere is only one material, which is why you use the same polymer on both sides of the weld. us, authorities will accept such a join without mechanical fasteners." (Offringa uses the word "join" here because the result of the welding process is not a joint, but one solid piece.) In fact, such welded TPC structures have been flying for decades. And although resistance welding and induction welding are the two most established methods, others, including ultra- sonic welding, laser welding and conduction welding, are being advanced for use with composites. Development of these methods continues as welding proponents seek the necessary reliability in predictive process simulation software, increased inline control of welding process variables, and extension of welding processes to production of aircraft primary structures. Resistance welding Along with KVE Composites Group (e Hague, e Nether- lands), GKN Fokker is an acknowledged leader in TPC welding development (see Learn More, p. 63). "We started with resistance welding in the early 1990s," says Offringa. "e elegance of this method is that heat is produced exactly at the weld interface." Electric current, passed through a resistive element at the weld interface, creates heat and melts the thermoplastic polymer (Fig. 1). However, this resistive element — a metal or carbon fiber (CF) — stays in the finished part. "We developed a method using a PPS-coated metal mesh as the resistive element, and then certi- fied and flew resistance-welded CF/PPS main landing gear doors on the Fokker 50 turboprop aircraft in 1998," says Offringa. "is then led to conversations with Airbus UK (Broughton, Chester, UK) and the development of glass fiber/PPS fixed leading edges for the A340/A350 and then A380 widebody aircraft." GKN Fokker has continued its resistance welding research, focused mainly on carbon fiber-reinforced plastic (CFRP). e technology has advanced. Premium AEROTEC (Augsburg, Germany) showcased an Airbus (Toulouse France) A320 rear pressure bulkhead demonstrator at the 2018 ILA Berlin Air Show. e bulkhead comprises eight press-formed CF fabric/PPS segments assembled via resistance welding. "We have been using resistance welding for some time," says Dr. Michael Kupke, head of the Center for Lightweight Production Technology (ZLP) for the German Aerospace Center (DLR) in Augsburg. "For the Premium FIG. 1 Advanced Thermoplastic Composite Welding Technologies

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