thermoplastic composites

Ultra-lightweight: how thermoplastic composites are changing aviation

redaktion
04.06.2018
8 minutes

The demands on materials and manufacturing processes in aviation are exacting: they need to be lightweight, stable, safe and cost-effective. Plastics have already shown themselves to be an alternative to existing materials on account of their positive properties, and increasingly thermoplastic composites are replacing aluminium and other metals in aircraft construction.

53 percent of the Airbus A350 XWB is already made of carbon fibre reinforced plastic (CFRP). We will explain what thermoplastic composites actually are and how they are changing the face of aviation.

Up to 70 percent less weight – that’s why aviation is relying on new materials

Competition for the cheapest passenger-kilometres is forcing a rethink amongst airlines and aircraft manufacturers. Every kilogramme of weight saved reduces fuel consumption and costs, which explains why there is a focus on lightweight constructions: the use of thermoplastic composites delivers up to 70 percent less weight than conventional materials. Optimised and automated manufacturing processes can also reduce production costs.

Many factors have to be considered when selecting materials to meet the stringent demands of aviation:

Environmental objectives as well as economic objectives, which overlap and complement each other. The most important demands include alternative fuels and their consumption, reduced environmental pollution, environmental design and the recyclability of materials.

Aircraft manufacturers, such as Airbus, are therefore seriously driving forward research in plastics technology, with even the company’s huge wings being made of carbon.

Where are fibre composite materials used in aviation?

Fibre composite materials are considered for a number of components in aviation:

Airbus A350: thermoplastic high-flyer

Airbus started it: for over 30 years the aircraft manufacturer has been using CFRP in all its aircraft. While its predecessors had to make do with very few carbon parts, an impressive 53 percent of the Airbus A350 XWB is manufactured from the lightweight plastic. Its carbon parts include the vertical stabiliser, upper and lower fuselage shells and the 32-metre long wings. Some 48 rolls of carbon fibre are laid for each wing shell at “CFK Valley” a total of 19,200 metres. The wings are pushed into an autoclave, almost 40 metres in length, to be cured: under 10 bar pressure and at 180 °C.

Watch the video to see how a wing is produced tape by tape:

Flexible, lightweight and ultra-stable: thermoplastics and composites

Thermoplastics – the ice cubes of plastics

Thermoplastics are plastics than can be moulded to any shape within a certain temperature range. When they then cool down, they retain their stable and durable shape. This process can be repeated almostas often as is needed, rather like an ice cube that is melted and can then be refrozen in a new shape.

Composites – hybrid all-rounders

Composites consist of a minimum of two components which are joined together:

  1. a technical fibre, which strengthens the product (for instance made of carbon or glass)
  2. and a plastic or polymer used as a binder matrix (for instance thermoplastics)

A distinction is made with composites depending on the length of the reinforcing fibres in the finished component. Reinforcing fibres several millimetres in length are referred to as long fibre-reinforced thermoplastics, while fibre layers and fabrics are known as endless fibre-reinforced thermoplastics.

There are different options for arranging the fibres in the matrix. The simplest method is to spray the fibres, which ensures a random arrangement of the fibres. More sophisticated techniques facilitate special structures, which significantly increase load-bearing strength, as is the case with layers.

Combining components results in properties that the individual components alone do not possess, including very high impact resistance, tensile strengthand vibration damping. This makes composites hybrid all-rounders.

Prepregs et al: thermoplastic semi-finished products

Semi-finished products represent the starting point for the aircraft parts of the future. Thermoplastic semi-finished products are generally produced in the form of plates, tapes, threads, pipes or rods, and have a solid or dough-like consistency. They are then further processed in various automatic processes to create a finished product. The semi-finished products have a wide range of flexible uses and can be processed in most diverse ways:

Prepregs (preimpregnated fibres)are the most common fibre-matrix semi-finished products in aircraft construction. Admittedly prepreg technology is one of the most expensive processes but ensures a very high quality of components. In this process, endless fibres are impregnatedwiththermoplastics (such as PEEK) and consolidatedunder pressure and at temperature. Prepregs boast excellent strength and rigidity, are fatigue-and wear-resistant, flame-retardant and insensitive to environmental influences. Plate-shaped thermoplastic prepregs are also known as Organo Sheets, and consist of fibre fabrics or layers.

Preforming: from semi-finished products to finished parts

Semi-finished products undergo complex manufacturing processes, most of which are specifically developed for these materials, to produce finished parts from the composites. High-tech robots are used in automated production processes, which lay, cut to size, drape and join the plastic sheeting together in micro-processes. Machines sometimes resembling huge ovens are used for curing.

Preforms are produced in preforming processes, which are then cured to produce the finished parts. The fibre semi-finished productsvery closely resemble the shape of the finished products and are produced from fabrics, layers or mats. They are then cut to size and joined to each other. In stacking, the layers are then stacked to create the required structure.

This video shows the complex production process of a carbon component:
https://www.youtube.com/watch?v=SkIN1FDlMkU

After preforming, the required components can then be produced in various processes. Positive pressure is used in the autoclave process to cure the material, while, in resin transfer moulding, dry fibres are wetted with resin and cured by heat. Fibre spraying, pressing and winding processes are also used. Modern hybrid moulding processes even combine several steps; the composite semi-finished products are moulded, then oversprayed and finally lacquered. We are excited to see where this journey is heading!

Cover picture © SFS

by redaktion

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