Changing the equation

The impact of composite materials on the design and manufacturing of civil aircraft has been immense over the last 25 years. From the low levels of around 10% of aircraft consisting of composites in the 1990s; now both Boeing, with the 787 and Airbus with the A350, use more than 50%. The weight reductions that these new materials offer mean that ever more efficient aircraft can be produced by the OEMs. However, there are drawbacks. Traditional composites currently used widely in aerospace, and the chemicals needed to bond them together, take more time to produce parts compared to their metallic equivalents. The drive to find composite materials that offer reduced cycle times is at the forefront of the sector’s research and development. One of the main areas of progress is a move away from thermoset polymers to thermoplastics. Now, polymer raw material specialist, Victrex has introduced a new Polyaryletherketone (PAEK) based product Victrex AE Composite, which it says has the potential to revolutionise the production of aerospace parts made from thermoplastics. “The major part of what we do is finding composite replacements for metal parts and when it comes to aerospace there is still a lot of metal that can be replaced on the aircraft,” begins Tim Herr, aerospace director at Victrex. “However, we believe there is also a lot of underperforming composite thermoset materials also. This is why we are using thermoplastic polymers combined with composites to offer what we feel is a compelling solution to the market.” Lighter and faster Victrex, whose PEEK parts have been used in aerospace for 25 years, produces its new AE Composites as unidirectional (UD) tapes and laminate panels which it says offer substantial benefits in terms of speed of component manufacture and installation. This new composite has shown to give weight savings of up to 60% under certain circumstances when compared to metals such as aluminium, stainless steel and titanium. “What’s special about this polymer is that it melts at a lower temperature and that affords many advantages,” Herr continues. “Firstly, it can be processed on existing equipment by most processers who use Polyphenylene sulfide (PPS). Additionally it can be overmoulded with our short-fibre reinforced Victrex PEEK polymers in a way that gives you a fully consolidated part with all the appropriate mechanical properties.” Effectively Victrex, through its hybrid moulding technology developed with the new AE Composite material, is offering something which bridges the gap between composite materials and injection moulding, enabling the production of complex composite components that were impossible to make this way before. Ryan Brady, Victrex global strategic marketing manager, explains: “With the addition of the overmoulding process you get all the benefits of composites, such as the specific strengths and the mechanical characteristics – namely all the reasons you would want to replace metal parts with composites – but with the design flexibility of injection moulding. That means our customers can, for example, take a component made of three parts and make it into one. This means you are not only reducing weight, you are also reducing costs and saving assembly time.” Taking the load Victrex AE Composites continuously reinforced components are designed to perform extremely well under load. Parts manufactured this way can include brackets, clamps, clips and housings used throughout the aircraft in primary and secondary structures, from the cabin including seats to the engines and fuel tanks. Herr affirms: “It was an achievement to invent a polymer and a process that would work. However, it was just as important to get a process that was manufacturable and repeatable enough for the aerospace market so that it could be proliferated. Now we have a very robust repeatable process that we can take to the existing supply chain base which allows them to make these parts.” Despite its lower melting temperature the new material fulfils all the FST properties required by aerospace. PAEK thermoplastics also offer better damage tolerance than thermosets, greater chemical resistance and fatigue performance whilst matching the strength and stiffness of thermosets. In comparison to metals they also offer improved corrosion resistance, processing speed and thermal insulation, according to the company. “We believe the industry will steadily move to thermoplastics, primarily because they offer reduced cycle times,” Herr adds. “With thermosets you have to cure them in an autoclave which can take considerable time; with thermoplastics an injection moulded part can be made in a matter of minutes as opposed to hours. “Most people in the industry consider PAEK materials as expensive, but it’s not just about the cost per pound aspect of the material. It’s about what it can do in terms of applications, how it can save time and manufacturing cost, rework costs, scrap reduction etc. There are all sorts of other ways in which you can save money by using this material and also make parts quicker for aircraft.” According to Victrex composites made from its high-performance thermoplastics are up to 60% lighter than AISI 4130 steel, a tough chromium-nickel-molybdenum alloy widely used in aerospace applications. They also achieve significant weight advantages over other lightweight metals including: TA6V titanium, 7075-T6 aluminium or ZK60A-T5 magnesium. The company says they are also stronger. For example, the specific strength of the composite is five times that of AISI 4130 steel. Another benefit of using thermoplastic materials is that they are 100% recyclable compared to thermoset alternatives. Thermoplastic materials can be easily reground compared to thermoset materials that need complex extraction processes if they are to be used again. It’s early days for this new material for use in aerospace applications but Herr is confident that in time it will be widely adopted by the industry. “We only launched Victrex AE Composite around a year ago. At the moment we’re making demonstrator parts so we can then share data results, costings etc. to help customers make informed decisions about the material. “This technology paves the way for components which can be manufactured more cost-effectively and with increased functionality and reliability,” he concludes. “We believe that our materials and technology solutions will continue to tilt market share in favour of composites in the aircraft construction industry. They help to reduce costs, achieve weight savings, offer more design freedom and provide durability and fast production times.” www.victrex.com/en Caption/images: Victrex AE Composites UD tapes and laminate panels Tim Herr: Victrex aerospace director A Victrex PEEK product made for an Airbus Helicopter(Copyright Airbus)