Offering improved manufacturing as a result of smarter designs, reduced costs, reduced weight and faster production rates, PAEK-based overmoulded composite solutions are increasingly finding interest with the aerospace design engineering fraternity, not least because of the favourable returns the solution offers in comparison to traditional materials like aluminium, stainless steel, and titanium.
In some instances, the weight reductions translate directly into significant gains in fuel efficiency and reduced CO2 emissions, whilst these composites materials demonstrate higher strength capabilities compared to the aforementioned metals.
One of the leading protagonists in this field is thermoset and thermoplastic advanced composite materials solution provider, TenCate Advanced Composites, who used last month’s JEC World Paris event to showcase its comprehensive range of advanced composite materials and a number of unique end-user applications.
Billed as its next generation composite materials for aerospace and high performance industrial applications, the company’s new thermoplastic and thermoset prepreg systems are said to feature enhanced processability and performance capabilities including an engineered PAEK-based thermoplastic prepreg that harnesses high performance mechanics with lower processing temperatures for aerospace applications.
Named TenCate Cetex TC1225, and suitable for overmoulding with PEEK, TenCate’s engineered PAEK composite materials enable form freedom and part consolidation in the highest performance applications.
Available in carbon and/or fiberglass-based UD tape, laminates and semi-preg fabric formats, TenCate Advanced Composites chief technology officer, Scott Unger takes up the story: “TC1225 is in the same family of materials as PEEK and PEKK, but the key benefit that sets it apart is that it has comparable glass transition temperature to both, and yet has a lower processing temperature.
“It also allows the customer to process closer to where polyphenylene sulfide (PPS) would usually process as a matrix, which in turn lowers the manufacturing stresses in the component because there are less thermal expansion issues within the part. Whilst it makes manufacturing easier, perhaps one of the most intriguing benefits is that it makes injection overmoulding easier too.”
But here’s the part where it gets really interesting. Unger says customers can now make composite parts from TC1225 and then overmould them with an injection moulding process using a short fibre reinforced PEEK material. Because the PEEK has a higher melting point than the TC1225 parent composite material, a very strong and aesthetically pleasing ‘thermal weld’ between the parent material and the injection overmould material can be readily obtained.
“It’s such a good interface between the two parts that it literally looks like the materials have been laminated together,” claims Unger. “TC1225 works very well with processing techniques like out-of-autoclave consolidation, stamp forming and continuous compression moulding and automated fibre placement – all these processes become a little easier when you can work with a material that has a lower melting point. It really enables a different perspective about how you make structural parts.”
A tough act to follow
“TC380 is a unique system in that it’s as mechanically tough as many of the toughest thermoset materials, but processes out-of-autoclave with a vacuum bag-only cure,” continues Unger. “It also has the ability to be continuously used hot-wet at 120°C, whereas as most high toughness materials are usually around 95-100°C, so it has high service temperature, good toughness, great mechanical properties and can be used out-of-autoclave.
“With most thermosetting out-of-autoclave systems, by the time the matrix has been toughened enough to make it suitable for an aerostructure, then typically the ability to use it out-of-autoclave, without high pressures to consolidate the laminate doesn’t really align very well. It’s taken TenCate a combination of ten years of research, and a couple of intermediate product launches in between to develop the technology and the manufacturing knowledge that it took to pull this whole system off. It’s a really unique product with some great properties.”
Unger reminisces by adding that when we think about the progression of materials in the aerospace sector, it all began with aluminium and titanium which served the market very well, but then fuel price increases and the desire to do things ‘out of the box’ changed the game for the airliners - and passengers - forever.
“There’s only so much we can do with aluminium structures to make them both efficient and light, and the OEMs have done this over the years to create very efficient structures and manufacturing processes - but in many cases, they are still too heavy! Titanium is a great material, but it’s very expensive to make aerostructures from and much more expensive than aluminium or CFRP. Indeed, it would be cost-prohibitive to make an entire commercial aircraft from titanium.
“Then the Boeing 787 came along, made largely from thermoset materials, and more recently the Airbus A350 XWB has entered the market offering similar usage levels of carbon fibre composites. The OEMs are looking more closely at thermoset materials - just like they viewed aluminium in the past in terms of how to make them more efficient. Thermoplastic materials are just one of the ways these OEMs want to improve structures; resin infusion is another, as well as out-of-autoclave epoxies, because thermoplastics aren’t perfect for every application, and nor are thermosets. There are areas that are ideal for thermoset applications and also those for thermoplastic applications too. Airframe OEMs will pick and choose where they will qualify the materials to best suit their needs.”
Fast track thinking
Clearly there are many opportunities for thinking out of the box with thermoplastics, but as Unger concludes, what is really driving the latest design initiatives is part manufacturability.
“The OEMs want to make parts quickly, with consistent part quality and using automated or semi-automated processes to eliminate where possible, manual labour. This is where all the real cost is in making many thermoset composite part – hand laid-up parts are simply too cost-prohibitive from a labour perspective.
“Airframers want to reduce the weight for efficiency and carry more passengers and cargo. However, one of the intangibles that the airline operators perhaps don’t really market well enough is that because CFRP is a stronger material, an aircraft fuselage can be pressurised at a higher pressure to make the passenger feel more like they are flying at a lower altitude. It makes them feel much more comfortable because the cabin environment isn’t sucking all the moisture out of the air.
“Further, composite materials do not corrode, so the aerostructure can handle more humidity inside the cabin. Passengers will feel much more refreshed when they fly long-haul on an all-composite aircraft. Airlines really should be doing more to market the comfort and passenger experience. It’s all about what composite materials can do that other materials can’t. These are the kinds of issues that are really driving the industry.”
