CompositesWorld
Issue link: https://cw.epubxp.com/i/944580
NEWS CompositesWorld.com 35 ISC of TPCs, Part 1 Although these systems are equipped with rollers that compress the material immediately after placement to ensure adhesion and avoid formation of air pockets that would create voids, consolida- tion of the laminate still typically occurs in the second step of what remains a two-step process, under a vacuum bag, in an autoclave, oven or other heating device, such as a heated tool. is state of the art persists, at least in part, because today's certified aerocom- posite materials are predominately thermoset-based. ere is an alternative. In fact, there has been one for decades. Known as in-situ consolidation, it means, consolidation in place. e key is the use of thermoplastic rather than thermoset matrices. ermoplastic materials are liquid when heated to melt tempera- ture and solidify when cooled, but do not need to crosslink like thermosets. Consolidation of a thermoplastic composite (TPC), then, can be accomplished by quickly heating the impregnated reinforcement to the melt temperature of the thermoplastic polymer matrix and then applying pressure as the tape or tows are placed onto a tool and/or a previously placed laminate. True in-situ consolidation (ISC) is a one-step process — no further heating or pressure steps are required after fiber placement or tape laying is completed. e implications of eliminating an entire and expensive step in the manufacturing process are so significant and obvious that one might ask, why isn't everyone already doing it? For one (there are other reasons, to be discussed), the aerospace industry pays a very steep price for change. Materials substitutions inevitably require extensive and costly testing and recertification. at said, two-step consolidated TPCs are already in use in select aircraft applications. Although their processing tempera- tures are much higher than thermosets — closer to 400°C vs. 180°C/350°F for primary structures — their cycle times are much shorter because TPCs require only cooling rather than cross- linking. ermoplastics also are inherently tough, and need no special formulation to provide the fatigue-resistance necessary for aircraft applications. Further, because thermoplastics can be reheated and reformed, they can be welded (a cost-saving, fastener-free assembly option). As the aircraft industry pursues materials and processing options that will enable production rates of at least 60 aircraft/month and support the envisioned digital manufacturing, multifunctional structures and sustainability that are deemed necessary for next-generation aircraft, TPCs have emerged as frontrunners. In an impressive percentage of recently completed, large-scale aircraft demonstration projects, TPCs have been the material of choice. In this first of a two-part series, CW explores the history of ISC TPC structures, memorializing the almost four decades of devel- opment that has laid the foundation for this one-step technology. In-situ early on Development of TPC aerostructures began in the 1980s in e Netherlands. Fokker Aerostructures (Hoogeveen) and Fokker Technologies (Papendrecht) — both now part of GKN Aerospace (Redditch, UK) — started work with materials supplier TenCate (Almelo) that "resulted in the J-nose for the A330/A340 and then the A380," recalls Henri de Vries, senior scientist, composites, in the Structures Technology Department at the Netherlands Aerospace Centre (NLR, Amsterdam). A research institute that supports the Dutch aerospace industry, the NLR began working with Fokker and TenCate, and is now touted as one of the aviation industry's great reservoirs of TPC knowledge. "In 1986, we had a high-temp autoclave, Fokker had facilities for press forming and resistance welding, and TenCate had the ability to make flat panels," de Vries continues. Glass fiber/PPS J-nose technology was developed using press-molded ribs and an autoclave-cured skin. ough these were not ISC structures, they were the first TPC structures to fly and pioneered the use of resistance welding, a process that de Vries says, "was unique at the time." (See Learn More, p. 38). FIG. 1 ISC via AFP In-situ consolidated thermoplastic composites are typically made using auto- mated fiber placement. This machine by MIKROSAM can process thermoset, dry fiber or in-situ consolidated thermoplastic composite materials, the latter most commonly built using laser heating. Source | MIKROSAM