The 777X’s wing, the largest composite part ever made for an aircraft, is produced in the new Composite Wing Centre at Everett. Mark Broadbent reports
COMMERCIAL BOEING 777X
At 105ft (32m) long the Boeing 777X’s spars are the largest singlepiece carbon fibre reinforced plastic (CFRP) composite parts ever developed for an airliner. Along with the wing’s panels, the spars are produced at the new Composite Wing Centre (CWC) that Boeing has built specifically for the 777X at the Everett home of the Triple Seven.
The CWC produces four spars (front, rear, right and left) and four panels (upper, lower, right and left). Another factory, Boeing Fabrication in St Louis, Missouri, supplies the wing’s leading and trailing edges, ribs and folding tips.
Building spars
Kevin Bartelson, 777X Wing Fabrication Leader, gave AIR International a detailed explanation of the work undertaken in the CWC, which covers 1.2 million sq ft (124,000m2) in area.
The build process for both the spars and panels begins in the clean room, where carbon fibre pre-preg tape (pliable and uncured carbon fibre with resin) is laid down. Next, the parts are moved using automated guided vehicles (AGVs) to post-care for curing in the autoclave and subsequent trimming and inspection. The AGVs move components, work stands and robotic arms around the factory floor.
Bartelson first explained the build process for the spars. Two automated fibre placement machines are used to lay down the tape for the spars (one machine for the front spar, one for the rear). An automated gantry picks up the head of the machine and runs it back and forth along the length of the spar to lay down the carbon fibre. The gantry can drop the head of a machine, pick up another head and return to work within two minutes.
The head has 16 spindles on it and with each spindle laying down 0.5in (12.7mm) of tape the machines lay down 8in (203.2mm) of tape at a time. More than 100 layers of tape are required to build up each spar.
Bartelson said: “We lay the tape in various directions. We lay it down with zerodegree direction the length of the spar, a 90° direction and plus 45° and minus 45°. That gives it strength characteristics in all directions.”
The automated fibre placement machines have been supplied by ElectroImpact. Bartelson said: “These are their newest generation of machines. The next aircraft programme will get the next generation, but right now we’ve got the fastest machines that do things other machines can’t. We’re laying a half-inch tape around a pretty complex contour; no one’s ever done that before.”
Autoclave
A layer of fibreglass is added to the spar before an AGV transports the tool with the spar on it through a cross-aisle in the CWC building to the autoclave. A ramp will be lowered to enable the AGV to load the spar into the autoclave. The AGV will then be withdrawn, the ramp lifted and the autoclave door closed and locked, allowing the cure cycle to begin.
Bartelson said: “Most cures are around 350oC [662oF] and somewhere between four and ten hours long, depending on the parts you’ve got. They’re always pressurised. When you pressurise, you’re putting a vacuum bag on the part and pushing down with pressure, making sure you get all the air out and a solid laminate.”
The systems required for pressurisation and nitrogen generation, and a need to minimise noise, means the autoclave is, in Bartelson’s words, “a building within a building”. The CWC will eventually have three autoclaves; each is 28ft (8.5m) in diameter and 120ft (36m) long – large enough to fit a 737 Classic fuselage inside it.
Post-cure, the autoclave doors will be opened, the ramp lowered and the AGV will go in and pick up the spar, bringing it out into the aisle. The vacuum bag will be removed and the part taken out of the mould.
Overhead cranes will take the spar for non-destructive inspection (NDI), where a robot will spray water at the part and send a signal through it to check whether there is a solid laminate.
The crane will then take the spar to a routing machine for trimming and drilling. After washing and a second NDI test to ensure there has been no delamination during the trimming and drilling, the spar will be painted.
Producing panels
The four wing panels produced in the CWC have two basic pieces: the skin and stringers. Just like the spars these parts are prepared in the clean room, but the CFRP material for them is laid down in a separate part of the room to the spar, and it is laid down in a different way.
The skin is made by an automated fibre placement machine controlled by a gantry laying down more than 100 plies of 1.5in (38.4mm) tape. Bartelson said: “It looks stiff but it’s soft; literally, if you tried to pick up a corner of it you’d ripple the whole thing.”
Unlike the machine used to laminate the spars, which has spindles, the one used to lay down the tape for the skins has reels. Bartelson explained Boeing has found that a reel system works well for achieving the gradual contours a wing panel needs, while spindles are better for achieving the radical contours of a spar’s u-shape.
The stringers provide stiffness along the length of the panel and are made by putting together an L shape, two L charges and what is termed a noodle to fill the triangular gap created when those three other parts are put together.
A base charge is laid out flat on top of this assembly, which is sent to the autoclave for curing. The 777X’s wing has 86 stringers, divided between the four panels (23, 23, 20 and 20 respectively). Each stringer is 108ft (32.9m) long.
After the stringers are formed they will be sent directly to the autoclave. Two lifting fixtures called OHMEs (over head mechanical equipment) will be responsible for moving, lifting and rotating the stringers; one fixture is used for ten of the 86 stringer configurations and the other fixture for the other 76 configurations.
Bartelson explained: “An overhead crane will come along and pick [the OHME] up and take it over to where we’ve built a stringer. It’ll drop down and pneumatically pick the stringer up. That’s why it has the rotating feature, to set [the stringer] down in another location. It’s a way of turning the stringer to work on either side of it. The system can both lift and rotate, so the stringer will not twist.”
After curing, the stringers will be trimmed and NDI checked before being applied to the as yet uncured skin. The wing panel assembly with the soft, uncured skin and the hard, baked stringers attached will next go to the autoclave where the hard stringers will bond to the uncured skin to create the completed panel. This process is called co-bonding.
Post-cure, the finished panel will be demoulded. A crane will lift the panel and rotate it to a vertical position for an NDI test. It will be trimmed, inspected again and drilled before it is washed and painted and some brackets and clips installed.
Assembly
When the work on the panels is complete in the CWC, the panels will be sent directly across the Everett site to the main 777 final assembly building. When the spars have been fabricated, however, they will be moved to a separate facility, Building 4002, for subassembly work.
Holes will be drilled into them and fasteners, stiffeners and rib posts installed. Much of this work will be automated using machines supplied by the Spanish company MTorres, but more complex subassembly activities such as installing pinions will be done manually.
After this work is completed, the spars will be moved to the main final assembly building where they join the panels from the CWC and the leading and trailing edges, ribs and folding tips, which will have arrived from St Louis. Wing assembly will then begin.
Bartelson explained there will be a change in the wing assembly process on the 777X: “Traditionally, we’d take two spars, attach the ribs to them and you get this funny-looking ladder; the ribs look like steps. Typically, we do that in a vertical position.”
On the 777X, however, the spars and ribs will be joined on a horizontal build line. Following drilling, fastening and sealing of the spars/ribs assembly, the upper and lower panels will be installed, which will be followed by further drilling, fastening and sealing. Leading-edge and trailing-edge panel installation and in-tank work will follow before the wing-to-fuselage body join. The folding wingtips will be attached later.
“The processes are new and specific to us. All the tooling and equipment is designed to build these specific parts. There’s not another one in the world like it. Everything is unique.”
Automation
With the laminating machines, the AGVs and the OHMEs there’s an impressive extent of automation in the CWC. Bartelson said this helps efficiency and ergonomics: “When you lay down this type of material by hand you’ve got to use cloth to form it to the product.
There’s 100-plus layers of tape on the spar; can you imagine 100-plus layers of cloth that you’ve got to cut out? What we’re doing here is using the machines for what they do well and our people for what they do well.”
Automation also helps safety. Highlighting the fibre placement machine in spar build, Bartelson said the machine will not pass over any people on the factory floor. When it is dropping or picking up a machine head it passes over to an area where there are two cradles.
He said: “It can drop its head in one of those slots and then the machine can go pick up another head or go park. Then this robot picks up the head out of that interactive area and presents it and it shuts down completely. It’s a little feature we’re pleased with; we’ve got to keep our people safe.”
Practice work
In 2016, Bartelson said, the focus with the CWC was completing building work on the facility and installing equipment. This year it has been about building practice parts, as part of the wider focus in the 777X programme to build maturity.
Practice spars, skins and stringers were produced, with the parts then cut up and analysed to verify the components being produced by the CWC were as expected; at the time of AIR International’s interview, for example, up to 100 stringers had been built, cut up and analysed.
Producing multiple test samples of parts has also been useful in verifying the manufacturing procedures and processes. Bartelson observed: “Even if [a part] is perfect it’s not production worthy until we prove we can do it more than once.”
Building such maturity matters, because everything in the CWC is point designed. Bartelson said: “The processes are new and specific to us. All the tooling and equipment is designed to build these specific parts. There’s not another one in the world like it. Everything is unique.”
With the test samples confirming this maturity, the CWC started work on the first production parts in mid-2017. The first spars and complete panels with co-bonded stringers for the static test airframe were built in the summer, with the first parts for the initial flight test aircraft entering the production process in September.
