Thermoplastic composites will play a significant role in the next generation of commercial aircraft

Web Industries’ global thermoplastics market development manager, Jim Powers and Web Industries and Omega Systèmes’ director of sales Europe, Patrick Markert, look at how thermoplastic composites can offer lightweighting opportunities and green benefits in aerospace applications.

Aerospace companies are selecting thermoplastic composites for a broader range of applications than ever before, even as research programmes try to unlock the materials’ full potential. The surge of activity is easy to understand. Thermoplastics play a vital role in the effort to ‘lightweight’ aircraft, which promises lower fuel consumption and greater sustainability. Additional benefits include improved manufacturing efficiencies and possible recycling of used thermoplastic parts.

Aerospace manufacturing technologies using thermoplastic composites will require commercial-scale formatting capabilities to support projected industry build rates

Precision formatters and converters support these initiatives by linking materials manufacturers with aerospace companies and component fabricators. The formatters convert thermoplastic prepregs into formats that are optimal for sustainable fabrication into completed parts.

The appeal of thermoplastic composites for aerospace stems from their unique composition and properties. They consist of semicrystalline polymer resins combined with carbon, glass or other fibres to form prepreg systems. Material producers can alter the ratio of resin to fibres to deliver specific characteristics, such as improved mechanical performance or faster cycle times.

Aerospace-grade thermoplastics include PEEK (polyetheretherketone), PEKK (polyetherketoneketone) and PPS (polyphenylene sulfide). They exhibit superior chemical and heat resistance and are capable of withstanding high mechanical loads in aerospace applications.

Thermoplastic materials require higher processing temperatures than thermosets, a competing material, but they have advantages in other areas. Unlike thermosets, which need a curing cycle that can last as long as 12 hours, thermoplastics typically require no curing after processing and have an unlimited shelf life at room temperature. Also, they can be melted down and recycled.

Precision formatters typically receive parent rolls of prepreg materials from thermoplastics manufacturers. The formatters slit the material into narrow tapes, which are wound onto spools for further processing. Experienced formatters provide spooled material in formats that are customised for the major types of fabrication equipment, including automated fibre placement (AFP) and automated tape laying (ATL) machines. Both methods are used to make large, complex aerostructures. AFP lines employ robots to lay down continuous fibre-reinforced tape and build structures one layer at a time. ATL machines produce large flat or mildly contoured structures using unidirectional tape.

Lightweighting potential

Thermoplastic composites were first used in small components, such as brackets and clips, but are now being specified for various structural components, including stringers, spars, wings and fuselages. Lightweighting is a key reason. Its potential can be summed up in a single statistic: thermoplastic composite parts weigh up to 40% less than conventional aluminium parts or other metal parts.

A typical aerostructure fabrication operation utilising thermoplastic slit tape in AFP and ATL machines

Lightweighting offers the promise of a new generation of sleeker, more sustainable aircraft. Lighter planes require less energy for propulsion, decreasing fuel usage and related costs. This promotes a reduced carbon footprint and more eco-friendly operation.

Despite higher initial material costs, thermoplastic composites have an impressive overall ‘buy-to-fly’ profile compared with competing materials. When cradle-to-grave costs from production through service life are factored in, along with lightweighting options and green-related benefits, thermoplastics can be a cost-effective option in many applications.

Streamlining production

There are significant opportunities to improve the manufacturing of thermoplastic components in ways that support high volume rates for aerospace programmes. Many are near term developments that will likely help commercialise the materials being considered for the applications. These include consistent in situ forming fabrication methods, eliminating any post processing such as autoclave or thermal oven requirements, developing a repeatable solution to welding unidirectional tapes together to combine parts, incorporating lightning strike material without laminate degradation and creating large parts such as co-consolidated structures in one operation. There are additional processes that can potentially support the high- volume TPC production necessary to meet increasing demands for primary and secondary structures in commercial aircraft.  Continuing research is underway at each stage of the manufacturing process.

One example is the Clean Sky initiative, a European public-private partnership that funds and coordinates research activities to produce more environmentally-friendly aircraft. Clean Sky’s Multifunctional Fuselage Demonstrator (MFFD) project is developing an 8m long fuselage section made entirely of thermoplastic materials. It consists of upper and lower fuselage halves fitted with stringers, frames, cabin and cargo floors and other interior elements. Once the halves are completed, they will be welded together without fasteners or holes. The assembled fuselage is expected to weigh 1,000kg less than a comparable one made from conventional materials.

As this project demonstrates, the use of thermoplastic components can reduce the number of fasteners needed in next-generation aircraft. Compared to conventional fastening techniques which are time-consuming, the drilling, fastening, and inspection operations can be eliminated. Depending on the application, production speeds theoretically can be increased as much as 500%.

Reducing waste

At an earlier stage in the process, materials manufacturers and precision formatters are collaborating to reduce waste and make processing methods more sustainable. In a recent case, a materials manufacturer found that its practice of trimming thermoplastic rolls along the edges during the manufacturing process produced excessive scrap material. The trimmings went straight into the waste basket. The manufacturer discussed the issue with its formatter, who agreed to accept wider rolls of material that improved the formatter’s throughput and increased output yield. When the formatter slits tape at the edges, it now collects the trimmings and returns them to the manufacturer for recycling. The result has been reduced overall waste and near 100% utilisation of thermoplastic materials.

Recycling options

The ability to recycle thermoplastic parts is an added advantage. They can be melted down to separate the embedded fibres from the thermoplastic resin. A structural aerospace component reaching the end of its service life could be designated for recycling. It might be reshaped and repurposed for a less taxing aerospace application or another use. The repair of damaged parts or parts with defects is also a possibility. Research is underway to work out the technical issues involved and to make thermoplastic recycling a reality.

Partnering benefits

Aerospace companies and component fabricators can benefit from partnering with precision formatters with proven aerospace-sector experience and extensive technical capabilities. Formatters should also be adept at developing innovative solutions to new challenges and scale up quickly to meet demand.

Look for thermoplastic composites to play a significant role in the next generation of commercial aircraft. As aerospace companies explore the full capabilities of these versatile materials, they can rely on their supply partners for technical ingenuity and innovative support.

www.webindustries.com

Mike Richardson

Mike Richardson

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Source: https://www.aero-mag.com/clean-skies-ahead/