Once an aircraft engine or body part has been designed, it needs to be casted, machined, extruded or 3D printed. Coatings also play a key role in parts design reports Boris Sedacca.
The use of composites in Aerospace has come a long way since they were first tested by the US military about forty years ago. Subsequent research, testing and technological developments in the design and manufacturing process of composite materials have led to an expansion in their usage in other segments of the Aerospace industry.
According to a market research report by Visiongain titled The Aerospace Composites Market 2012-2022, this is evident in the introduction of new aircrafts such as the B787 Dreamliner and that of the A400M military transport aircraft. The range of composite materials available has also extended too.
Fibre-reinforced materials can now include glass and carbon, thermosets composites such as aramids and metal and ceramic matrices. Whilst initially, composites usage was limited to the secondary structures of aircraft, better understanding of the physical attributes of composite materials has led to increasing usage in primary structures such as airframes.
The light-weight, strength and non-corrosive quality of composites make them attractive to the Aerospace industry. For aircraft users who are keen to keep fuel and maintenance costs down, the development of aircraft which make use of substantial composite parts is particularly appealing.
Overall, the Aerospace composites market is characterised by strong and steady growth. North America, Japan and Europe are the dominant markets but the global economic crisis coupled with low labour rates and improvements in the production process from emerging markets will contribute to a shift in market share away from those more mature markets. As such, the rate of growth of the global market will be dependent on how national markets such as China, Brazil and India develop high end and high value composite materials which can be used for aircraft.
Saab has extensive experience and well equipped facilities to meet the demanding test requirements of the modern Aerospace industry. For 60 years the company has performed structural testing of specimens ranging from small components to complete airframes. Its Aerospace customers include Airbus and Boeing and it uses a range of standardised test equipment or designs and manufactures tailor-made test rigs, with operations certified to ISO 9001 and AS/EN 9100.
Aside from structural testing, the department for structural and environmental testing at Saab contains resources for mechanical and electrical (EMC) environmental testing, and employs about 30 people of which about 20 work with structural testing. At its Linköping office it has two facilities for full-scale testing and two for component testing. The environmental testing is spread over three other facilities, one for vibration and climate testing, one for rain erosion and one for EMC.
Jan-Åke Bjärkmar, manager for structural and environmental testing at Saab, told European Design Engineer: “Our experience is primarily in testing of aircraft body materials. We have resources for static and fatigue testing of aircraft structure, from Catia software design and manufacturing of the test rigs to strain gauge installation, data acquisition, control system management, test management, inspections, non-destructive testing and reporting.
“There is dedicated equipment for full-scale and component testing such as control systems, data acquisition systems and hydraulic supply at four test sites, two with strong floors. Most of the testing is verification testing, verifying the stress analyses on products designed by Saab as a part of the verification and certification processes. The feedback relates to areas such as internal stresses, static strength, fatigue sensitive areas and crack propagation rates. Sometimes we do development testing of new design solutions.
“In the past we have done all structural testing for Saab aircrafts such as Viggen, Gripen, Saab 340 and Saab 2000. We are also doing verification testing on structural parts that Saab develop and manufacture for Airbus and Boeing. When we have capacity we also offer testing directly to external customers.”
Most of the testing is on metallic or carbon fibre composites. On composites, testing is sometimes made under ‘hot & wet’ conditions at the component level. Test stations monitor up to 94 control channels on servo-hydraulic actuators ranging from 1-900kN, load-cells ranging from 0.5-500kN, capacity hydraulic load frame to 1,000kN, equipment for air pressurisation and position and strain measuring equipment.
Though the materials and composites market is dominated by large players like Saab, smaller players can also get a look in from time to time. In January 2013, Alenia Aermacchi, part of Finmeccanica, signed a contract for panels from Czech company Aero Vodochody to build a fuselage section for the Airbus A321. Aero Vodochody will produce up to 96 panel sets a year in a renewable contract initially valued at over 120 million Euros.
Ladislav Simek, president of Aero Vodochody, said: “The contract for A321 fuselage panels is a result of our long-lasting cooperation with Alenia Aermacchi on C-27J Spartan aircraft. Aero Vodochody is responsible for producing the centre wing box.
“After some problems with the C-27J Spartan program, there was a significant drop in orders, so Alenia Aermacchi decided to offer Aero Vodochody the production of A321 fuselage panels. The first set of panels should be produced by the end of 2013. We have just bought a new Integrated Panel Assembly Cell (IPAC) CNC automatic riveting machine, so it will be able to produce the fuselage panels very quickly.”
At GKN Aerospace, composite material processes include automated tape laying, double diaphragm forming, automated fibre placement, resin transfer moulding, resin film infusion, liquid resin infusion, microwave curing and laser ablation.
Automated tape laying allows the rapid deposition of composite pre-impregnated tapes to either a flat or curved tool to produce complex parts. This method allows the deposition of both individual plies directly on the tool or may stack the plies in the correct orientation prior to placement on the tool.
Used on Airbus A400M composite wing spar and A340 landing flap, the advantages include reduced cost cycle time, manufacture of large structures up to 14 metres in one go, automated process and increased accuracy, repeatability and quality.
Double diaphragm forming forms flat composite material under heat and vacuum to provide complex shapes. Also used on Airbus A400M composite wing spar and A340 landing flaps, the advantages include use of different temperatures during the forming process, automated process, controlled forming and good quality and repeatability.
Automated fibre placement
Automated fibre placement of pre-impregnated composite fibres/tapes onto a tool at high speed provides several advantages to GKN Aerospace, including speed of deposition, reduced scrap, improved part-to-part uniformity, and reduced weight. The method is used on Airbus A350 XWB rear spar and trailing edge assembly, and allows steering of fibres and greater component complexity and features.
Resin transfer moulding reduces weight, cost and assembly time. Used on environmental lightweight fan blades, Lockheed Martin F-35 Lightning II front fan frame, Airbus A380 rudder actuator brackets and A340 rear pylon fairings, Saab Gripen weapon fairings and Taurus KEPD 350 missile wing, it provides quality and repeatability, integrated structures and accurate interface.
Resin film infusion technology was developed by GKN Aerospace and utilises a lay-up process that allows out-of-autoclave curing using either an oven or heated tools. Used on Efficomp, Tango spars, Awiator winglet and Airbus A380 trailing edge panels, it removes size and cost constraints of an autoclave, improves cycle times and quality, and offers the potential to reduce weight and cost, while allowing lean flow of product.
Liquid resin infusion is a process where dry carbon fibre material is laid into a tool. The carbon material can be pre-formed into 3D shapes. The resin is then injected according to precise requirements of temperature and pressure. Used on integrated wing programme and next generation composite wing programme.
Also used on integrated wing programme, microwave curing delivers direct heating to the part and does not require high pressure to be maintained inside the chamber. It allows a better coefficient of thermal expansion to be achieved between the part and the mould which means that more accurate complex components can be obtained.
The modular design of the microwave chambers allows them to be used in series so that materials can be passed through on a conveyor system. The equipment allows for metal items to be introduced into the process without the risk of arcing or damage. The process benefits from the heat up and cool down rates over a conventional autoclave.
Finally with the ability to be used on all composite structures, laser ablation works by removing the matrix or resin from the composite by vapourising the resin with a low energy density using a TEA CO2 laser. There is no contact during the process, avoiding the traditional machining and grinding where fibres may suffer local damage. The exposed fibres are brushed away until the repair is ready for replacement material to be bonded in place.
Composites withstand high temperature and cut weight
The diagrammatic image of a Boeing 777 (bottom image, left) demonstrates Henkel’s curing epoxy-based composite surface film, Hysol EA 9845 SF, which enables a 30 per cent weight saving, while a high temperature modified epoxy film adhesive, Hysol EA 9658, provides long term thermal durability.
Hysol EA 9845 is applied to the outer surface of a control panel surface for composite structures including wings, fuselage, control surfaces, engine cowling and fairings. EA 9845 is a composite surfacing film that contains a non-woven fabric designed to improve the surface quality of honeycomb stiffened composite parts. It reduces surface imperfections, provides a 30 percent weight saving compared to current surfacing films and minimises pre-paint preparation. In addition, lightning strike formulations are available.
Henkel claims aircraft manufacturers can save up to 30 per cent weight with Hysol EA 9845 SF. Through its low weight, the surfacing film is said to minimise core crush and reduces core mark-through. The increased resistance to UV radiation before painting eliminates the need for sanding and rework prior to painting. Even without sanding, Henkel maintains that EA 9845 SF guarantees good paint adhesion which increases the durability of the finished surface of the composite part. It can be cured from 120-176 degrees centigrade. The innovative Hysol EA 9845 SF can be applied to fuselage, wings, engine cowlings and control surfaces among others.
Hysol EA 9658 is a nacelle film adhesive that combines high temperature controlled flow to minimise hole blockage and flash/flow clean up, which Henkel asserts is three times as tough as industry-standard high temperature film adhesives and is suitable for metal, composite and honeycomb bonding where continuous exposure to temperature up to 177˚C is possible.