The portal bridge swings automatically into place above the black component. Attached to it is a swivel-mounted red support bracket with a fiber placement head that approaches slowly, emitting a soft humming noise. A filament of black CFRP is gradually being spun from each of the twelve bobbins positioned along the sides of the head. CFRP is short for carbon fiber reinforced polymer – and it is the reason the latest generation of aircraft are much lighter than their predecessors. All the major aerospace manufacturers have adopted the new material with open arms as it allows them to cut back on weight, save kerosene and slash expenses. The new material not only offers greater stability and is easier to process than aluminum or other metals, its outstanding benefit is that it weighs a lot less than conventional materials.
This 12.5mm wide CFRP tape contains more than 12 000 epoxy resin-soaked carbon fibers side by side and on top of each other.
The carbon fibers are soaked in epoxy resin and can only be handled with cotton gloves; this is to protect the material, which is still heat and pressure sensitive, and avoid skin irritation caused by the resin.
To give the material the necessary stability the CFRP tapes are laid in four directions, each at a 45° angle to the previous layer.
The placement head of the fiber-laying machine passes automatically across the upper wing shell numerous times.
The placement head has twelve bobbins of CFRP tape along each side; each bobbin holds 1 400 meters of tape; 350 rolls with a total of 490 kilometers of tape are needed to produce an upper wing shell.
Each placement head includes a heating element which heats the material to 40° C before laying it; this ensures that the layers of CFRP tape adhere better.
To ensure that the layers bond perfectly, the robot pushes them under a radiant heater; then it stops, lifts the placement head, spins it around by 180 degrees and starts back over the sheet. Gradually, layer by layer, the largest individual CFRP part ever produced in the aerospace segment emerges: The upper shell of the wing of an Airbus A350, which will be joining the Lufthansa fleet at the beginning of 2017.
“This machine is our latest fiber laying device,” explains Sandra Bube, 29. The slender technician smiles proudly. Bube grew up not far from the Airbus plant in Stade on the Lower Elbe, an hour’s drive west of Hamburg – and she has devoted her career to CFRP. Following an internship, an apprenticeship, a year as a machine operator and five years in equipment assembly, she recently qualified as a “Master of Fiber Composite Materials. She couldn’t have chosen a better place to follow this career path, as the use of CFRP in aerospace applications was practically invented in Stade.
CFRP accounts for 53 percent of the plane’s weight. In the 1980s, airplanes contained less than 10 percent.
“It started here as early as 1983, when CFRP was first used to make the rudders for the Airbus A310,” says facility manager Kai Arndt, 44. “In just over 30 years, we have built a truly impressive CFRP expertise here.” Back then, Lufthansa was one of the first customers for the A310; very soon, the carrier is due to take delivery of the first of 25 jets of the innovative A350 XWB series. XWB is short for eXtra Wide Body, describing the aircraft’s generously proportioned fuselage. The A350 XWB has another distinctive feature: no other aircraft has a greater proportion of CFRP. This composite material accounts for 53 percent of the plane’s weight. In the 1980s, airplanes contained less than 10 percent.
The new production hall for the A350XWB upper wing shells in Stade is gigantic. Staff use scooters to get around.
“CFRP is our black gold. It never ceases to amaze me how versatile it is,” says Sandra Bube, “and how rapidly the technology is developing.” Thanks to its low weight and high stability, CFRP is the ideal material for the aerospace industry and is swiftly replacing aluminum in the new long-haul jets. The A380 (maiden flight 2005) only has 22 percent CFRP, the Boeing 787 (maiden flight 2009) already has 50 percent, and the proportion of the A350 XWB (maiden flight 2013) has risen by a further three percent.
The basic ingredient in CFRP is oil; this is used to make carbon fibers, thinner than a human hair and exceptionally strong. The individual fibers are grouped in strands consisting of several thousand individual fibers that are soaked in epoxy resin. The CFRP filament that the new machine is laying is only 2.7-millimeter-wide – but contains a staggering 50 000 strands. CFRP can be used to make airplane parts that are reinforced in the places that are exposed to particular stress and are thinner elsewhere. This approach is used for the upper shell of the wing, the exterior skin of the upper sides of the A350 XWB. “The rear wing root, where the wing is attached to the fuselage, bears enormous bending forces, and we apply more than 250 layers of CFRP tape here; each layer is 0.25mm thick,” explains Bube.
The wing tips are a different matter: here, around 40 layers are sufficient to provide the necessary stability. With an overall length of 32 meters and up to six meters wide in places, the upper shell of the wing is made in a single piece and weighs 2.5 tons. It is an impressive component, and one which passengers on board a Lufthansa A350 will soon be able to admire from the comfort of their seats. “In terms of its size and dimensions, the wing shell is definitely the most complex CFRP component in the A350,” says facility manager Arndt. The placement head has to lay nearly 480 kilometers of the 1-centimeter CFRP tape in four different directions to give the component the necessary degree of stability exactly where the bending forces are greatest.
In Stade, the tail fins for all Airbus models are made of CFRP, including the nine-meter long tail fin of the A350.
The autoclave is a key component in the CFRP production process. The tunnel-sized pressurized container can take up to two wing shells simultaneously and is the largest serially operated autoclave in the world.
This special truck is used to move the 32-meter upper wing shells from the production hall to the autoclave. The 30 wheels on each side can also move sideways, just like a lunar vehicle.
This unit is like a gigantic pressure cooker: a gas-tight pressurized container that is closed with a round steel gate weighing several tons; it is nearly 36 meters long and nine meters wide.
The finished upper wing shells made in Stade, which are an incredible 32 meters long, give an indication of the vast dimensions of the wings of the Airbus A350XWB.
After the first session in the autoclave at 10 bar pressure and a temperature of 180° C, the stringers – which are also made of CFRP – are applied to the shell before it goes back in the autoclave.
At 53 percent, the Airbus A350XWB has the highest proportion of CFRP of all commercial aircraft; the composite material is used to make the fuselage, the wings, and the tail section.
Then the wing shell is shifted on to a special truck which, just like a lunar vehicle, can also move sideways, and is driven to the world’s biggest serially-operated autoclave. This unit is like a gigantic pressure cooker: a gas-tight pressurized container that is closed with a round steel gate weighing several tons; it is nearly 36 meters long and nine meters wide, and resembles a tunnel. Two upper wing shells can be rolled in simultaneously. The chamber is locked, gas pumped in to bring the pressure up to ten bars, and it is then heated to 180 degrees Celsius. “The first session takes 13 hours,” says Bube. In the next step, the longitudinal reinforcements are applied to the shell and the shell is treated in the autoclave for a further eight hours. “Pressure and heat fuse the fibers in the resin and cure them into the given shape,” explains Bube. Previously, making an upper shell in a three-shift production rota took around five days; in future, it will take only half the amount of time.