Thermoplastic composites (TPC) are not new to the aerospace field, but in the past few years, the use of thermoplastic materials in commercial aircraft has reached its peak. The application of TPC in small parts such as brackets or small internal components has been It has been a while, and currently thermoplastics are gradually entering larger aircraft structures, and are expected to play a greater role in future commercial aircraft.
International Thermoplastic Composites Focus Events in the Past Two Years
In March 2018, Toray Industries, the world's largest carbon fiber manufacturer, acquired TenCate Advanced Composites for 930 million euros. This move appears to enhance Toray's TPC capabilities and prepare for the next wave of commercial aircraft development. Shortly after the announcement, Hexcel and Arkema announced that they will combine Hexcel's carbon fiber manufacturing technology with Arkema's polyether ketone ketone (PEKK) resin to establish a strategic alliance to develop aerospace Thermoplastic composite material.
In April 2018, Premium Aerotec GmbH in Augsburg, Germany, launched the Airbus A320 pressure bulkhead demonstrator, which was developed and manufactured using carbon fiber in a thermoplastic matrix. The demonstrator is composed of eight welded sections, demonstrating the weldability of thermoplastics and how it has the potential to make aircraft parts larger.
Premium Aerotec's A320 pressure bulkhead illustrates the weldability of thermoplastics and has the potential to be used to manufacture larger aircraft components.
In August 2018, Solvay, Premium Aerotec and Faurecia Clean Transportation established the IRG CosiMo alliance, which is dedicated to the development of materials and aims to realize the processing technology for mass production of thermoplastic composite materials for the aerospace and automotive markets.
Since June 2017, Solvay has been working with GKN Fokker to implement large-scale aerospace structural improvements through the use of TPC. The company started PEKK polymer production in September 2017 and then doubled its qualified UD thermoplastic tape production capacity in 2018. In 2019, Solvay established a dedicated TPC research laboratory in Alpharetta, Georgia, USA to develop next-generation materials.
Teijin Ltd. of Japan Teijin Ltd. announced in January 2019 that its TENAX carbon fiber and carbon fiber/thermoplastic unidirectional prepreg tape (TENAX TPUD) have been certified by Boeing and can be used as a high-level intermediate for composite materials in major structural components.
With the advancement of thermoplastic composite technology and materials, people gradually pay attention to the role of TPC in the aviation industry in the next few decades is becoming more and more important. Manufacturers are interested in taking advantage of TPC's manufacturing advantages and fast processing time, and hope to use TPC to manufacture larger structures, such as fuselage panels and ribs. In addition, TPC has high fracture toughness, good mechanical properties, recyclability and low toxicity, and can be stored at room temperature. As OEMs and aerospace-grade suppliers become more familiar with thermoplastics, they have been used for more complex parts, welded components, and basic structures.
Processability of thermoplastic composites
A major reason why TPC finds its place in the aircraft industry is their machinability. Since thermoplastics have been completely polymerized, their productivity is faster than thermosetting plastics that must be cured. "When you look at the time it takes to make thermoset parts today and compare it to the time it takes to make thermoplastic composite parts, you find that thermoplastics are about 10 times faster," said Mike Favaloro, president and CEO.
Compared with thermosetting AFP, a major advantage of thermoplastic automatic fiber placement (AFP) is faster processing time and increased productivity. After in-situ lamination and non-autoclave (OOA) merge can save costs. David Leach, director of business development at ATC Manufacturing Company, admitted that the unit cost of thermoplastics exceeds the cost of thermosetting plastics, but he believes that the price of TPC materials will fall. In addition, processing efficiency provides opportunities to reduce costs today. The general consensus in the composites industry is that compared to thermosetting plastics, the current OOA thermoplastic process can save more than 30% of the cost.
Leach pointed out: "Even if the aircraft has been put into production, thermoplastics are entering the process. This proves the cost advantage of thermoplastics." The potential of high-performance matrix polymers has exceeded the range currently available on the market. Doug Brademeyer, director of Solvay's ultra-high polymer materials, said the company is developing tailor-made polymers tailored to different manufacturing processes internally and with partners. Brademeyer said: "We are excited about these tailored PAEK solutions and can quickly apply them to the commercialization of our assets worldwide based on customer needs."
Low melting point PAEK
As aircraft OEMs and suppliers compete to increase productivity and shorten cycles, processability becomes key. Polyetheretherketone (PEEK) has the largest database and the most extensive qualifications, and has long been the first choice for thermoplastic polymers. But Favaloro believes that low melting point polyaryl ether ketone (LM-PAEK) has some advantages, especially in automated processing methods such as ATL.
"PEEK can be processed by stamping and continuous forming, but LM-PAEK has a lower processing temperature and a lower working viscosity, which can achieve better automated processing, lower crystallinity, and lower residual molding stress. LM-PAEK has 350 -385℃ wide process window. For reference, the processing temperature range of polyphenylene sulfide (PPS) is 330-350℃, while the processing temperature of polyetherketoneketone (PEKK) and PEEK are 380℃ and 400℃, respectively. Scott Unger, CTO of Advanced Composites, said: "This material has gained such great appeal because of its processability. "
"The purpose of developing TC1225 is to create a product that can be easily processed at temperatures close to the PPS service temperature, which has a favorable cost position for the end user and has the mechanical and fluid resistance characteristics of PEEK," Unger said. "With TC1225 LM PAEK, I think we have achieved all these goals. Cetex TC1225 is currently being certified by the National Advanced Materials Performance Center.
According to reports, the use of LM-PAEK tape can increase the speed of placement. Tim Herr, Victrex Aerospace SBU Director, said: "We can achieve the unprecedented laying speed of in-situ AFP and AFP consolidation outside the autoclave." He said that 60 meters per minute can be laid on the oven consolidation panel . In terms of quality, Unger claims that low-melting PAEK provides the ability to use in-situ fiber laying to obtain the same laminate quality as fiber laying laminates, which are cured by oven curing after fiber laying.
Composite bonding
The solderability of TPC is a major advantage for materials used in aircraft development. Fusion bonding/welding finds alternative methods for mechanical fastening and using adhesives, both of which are used to join thermoset composite parts. Stephen Heinz, director of product development at Solvay, said: "Connecting and welding play an important role in the future of assembly, and it is possible to cut costs and improve the reliability of aerospace structures. Companies such as GKN Fokker are taking the lead in demonstrating welding technology."
GKN Fokker has been devoted to the development of TPC welding, and has been attempting resistance welding of thermoplastics since the 1990s. The company has been using a thermoplastic welding process to connect the tip's internal ribs and shell. At the 2019 JEC World Exhibition, the company showed a thermoplastic composite fuselage panel divided by region made with Solvay APC (PEKK-FC) UD tape. The result is the result of a joint R&D project between GKN Fokker and Gulfstream Aerospace. According to reports, due to the simple "butt" orthogonal grid reinforcement and fully welded frame, the part is the lowest cost composite plate.
GKN Fokker shows a regional composite thermoplastic composite fuselage panel
Arnt Offringa, head of technical development for thermoplastic composites at GKN Fokker, explained: "Using thermoplastics, you can greatly simplify orthogonal grids by "butting" the grid to the skin. "The grid now consists only of simple flat preforms These preforms are consolidated with the skin laminate to form a low-cost, overall hardened shell. Weld the frame to the grid. These welds are subjected to shear forces, so all bolts can be omitted. "
Although welded thermoplastic structures have been used on aircraft cabins for some time, the technology now appears to be ready for the main structure. Mike Favaloro believes that aerospace manufacturers and OEMs are increasingly confident in TPC, especially process control. He said: "In 10 years' time, we will see it become more and more widely used."
Recyclability
Another benefit of TPC is recyclability. Because thermoplastic polymers can be remelted and reshaped, some companies are looking at TPC as a way to reuse materials. One such recycling program operated by the Thermoplastic Composites Application Center and the Thermoplastic Composites Research Center focuses on the reuse of production waste from TPC processing to collection and shredding.
The TPC-Cycle projects of TPAC and TPRC focus on production waste from collection to shredding, reprocessing to application
The TPC-Cycle project is dedicated to the development of affordable and environmentally friendly recycling methods for the high-end, high-volume market, while producing recyclable materials that should retain as much of the mechanical properties of the original thermoplastic material as possible. The collaboration includes multiple industry partners from materials, manufacturing, design and applications, including GKN Fokker, Toray Advanced Composites, Cato Composite Innovations, Dutch Thermoplastic Components and Nido RecyclingTechniek.