Advanced Materials Land In The UK

The aerospace industry’s dogmatic pursuit of composites could make the material more accessible to other sectors, Justin Cunningham reports…



Aerospace design engineers like composite materials because of their outstanding strength to weight ratio. Composites mean lighter aircraft, which equates to more efficient flight and reduced operational costs.
Despite the many practical difficulties and pitfalls involved in its use, the industry has pursued its introduction with a stubborn persistence. Yet, even with the perceived advantages of using composites, most other engineering sectors have shied away from their use.
For starters, composites are expensive and time-consuming to produce. The material needs to be cured, repeatability is difficult and it is notoriously hard to automate manufacture. It is an engineering minefield that has led to fierce debate between designers and their production counterparts. But this seems to be changing.
“Composites are the future,” says Marcus Bryson, chief executive of GKN Aerospace. “It is important that we are developing technology that is going to be around for 20 years, unlike some of the other work that is metallic.”
In the longer term, composites will allow designers to get away from the restrictions metallic’s place on aircraft. Aircraft structures, at present, resemble flying cigar tubes with wings. The reason is the limitation in the materials available.
However, composites such as carbon fibre reinforced plastics will allow for far more exotic designs, such as blended wings – already successfully demonstrated by the Northrop Grumman B-2 flying wing. Additionally, Boeing has been researching a Blended Wing Body concept, a large passenger aircraft that is only possible because of advances in composite material.
Nearer term, composites are allowing engineers to design larger one piece structures, reducing parts count and weight. However, designers are still being limited by what can actually be manufactured. As manufacturing technology advances, so too will the ability to evolve and revolutionise conventional designs.
From fishing rods to bike frames to flak jackets, if an applications needs high-strength and lightweight, composites are unrivalled. As fuel and energy efficiency become prevalent in the transport sector, so will the need to lighten structures. In all industry sectors, composite materials have a big role to play in removing weight while maintaining – and, in some instances – improving strength and rigidity. Additionally, the ability to orientate the fibres in multiple directions means that the properties of the composite material can be tailored to the application.
However, despite its favourable design characteristics, factors such as higher cost and relatively slow manufacture often deter potential users.
GKN has invested heavily in developing the manufacturing technology, opening its advanced composite research centre on the Isle of Wight in 2005. It wants to enable automated composite manufacture, which will primarily benefit the aerospace industry.
However, the increased use of the materials will help to lower production cost and allow industries with higher throughputs – such as automotive –to begin explore its use.
Phil Grainger, GKN’s senior technology director, says: “The ability to manufacture complex and larger parts in one go has so many assembly hours benefit. Carbon fibre is better on weight but, at the moment, it costs more. We want to get it competitively priced against aluminium products, but with all the other benefits.”
Although the company has seen a vast expansion of its defence business in the US, it saw a good opportunity to bring composites to the UK and develop the technology. “In terms of doing it in Europe, that is my preference,” says Bryson. “If we develop the technology in the UK, we take it anywhere we want to. If we do it in the US, it is more difficult to get the technology out.”
The investment has continued and the company recently took ownership of Airbus’ Filton wing manufacturing operation. Although much of the current work at the site is metallic, Airbus has been at the forefront of composite material technology development. As a result, it has increased the amount of composite in aircraft designs such as the A380 and the A350.
The A380 Superjumbo airframe is made up of some 25%, by weight, of composite material. And the A350XWB, due to enter production in 2010, will be made up of around 50% composite material. As a result, many of the shop floor staff can expect to retrain on the material in the coming months.
Pete Bermingham, head of assembly business, explains some of the changes: “If it was all-composite design, it would be easy. If it was all metallic, it would be easy.”
The problem comes, for example, at the trailing edge, where different types of material tend to be stacked. Dealing with these stacks requires skill.
“If you have a composite spar, an aluminium rib and then titanium, the hardest stuff you are drilling is at the end and all the swarf is going up through the composite, which can damage the fibres,” Bermingham adds. “Developing that drilling technology and getting it right is really crucial.”
Engineers working on the design of the new aircraft have had to carefully assess where stacks of materials are and the effect which the joins will have on the overall structure. However, an ongoing concern is the rate of production that will be required.
GKN is continuing to develop key manufacturing technology, such as automatic tape laying (ATL) machines. These are generally used to lay-up flat composite, which is then put through hot drape forming machines that press parts into shape while simultaneously partly curing them. Automatic fibre placement (AFP) machines are also being developed. They can lay-up over curved surfaces and use a number of narrower tapes.
The company has successfully used ATL machines and hot drape forming to manufacture the A400M wing spar. However, the larger A350 spar will need a much higher rate of production and is placing a need for the company to refine the process.
“If you look at the A350, it all starts to become a lot more mechanised,” says Bryson. “It is a highly capital-intensive process. The investment we are making, in terms of tape-laying machinery and technology, takes the composite manufacture to a new level.”
The accuracy of the parts being produced from composites is also rapidly improving. Where parts used to have to be machined to tolerance, GKN has demonstrated with the A400M wing spar the accuracy that is possible from the process, a tolerance of just 0.5mm in 14m. This reduces tooling and assembly time, as what used to be several parts is now a single component that needs only a minimum amount of machining.
The company is also keen to keep the curing of composite out of large autoclaves, which is a time consuming process. As a result it is researching and developing microwave curing.
“We have been looking at this for some time, but it has not yet been successfully deployed,” says Phil Grainger, GKN’s senior technology director. “But we are making headway with it. As a result, we could use this instead of autoclaves, allowing single piece flow.”
The UK aerospace industry is likely to be a key player in the development of composite technology and is already setting-up supply chains. For design engineers, it means the technology and materials availability will increasingly become available in the UK.
“It’s introducing major composite technologies in to the Bristol area and that is where we believe the growth is going to be,” says Bryson.


Advantages
· Offers superior strength to weight ratio to metallics
· Formability: can be shaped to almost any contour
· The ability to make larger single piece components
· Directional strength can be tailored to suit the application by different fibre orientation
· Longer life: composites do not corrode

Disadvantages
· More expensive than metallics
· Manufacture is time-consuming and can be problematic
· A lack of practical design data from real-life use
· Internal damage can remain hidden
· Virtually impossible to recycle


Pointers
* The aerospace industry is driving technology to automate the manufacture of composites
* The material will allow lightweight and extremely strong structures
* The material properties can be tailored to suit function and application

Author
Justin Cunningham

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