Guy Norris/SEATTLE
Late next month a 747-400 destined for Japan Airlines (JAL) will roll out of Boeing's Everett manufacturing site in Washington. On the outside it will look just like any other -400, but a close inspection will reveal a different story.
This aircraft, line number 1236, is the first fuselage to be completely assembled using a "snap together" technique known as FAIT - or fuselage assembly improvement team. FAIT was made possible by another initiative, proposed in 1994, known as AFA, or accurate fuselage assembly. AFA and FAIT are symbiotic and form a two-pronged attack by Boeing and 747 fuselage maker Northrop Grumman on cycle time and cost. The exercise's goal is a 40% cut in assembly flow time over the next five years. It forms a major element of the company's aim of being able to reduce to six months the time span from the start of construction to delivery - less than half the current time.
AFA used Boeing's now standard IBM/Dassault CATIA (computer-aided three-dimensional application) system to digitise the original mylar engineering drawings, many of them dating from the 1960s, of the skin panels and associated hardware. The CATIA data are used to drive numerically controlled equipment to produce precisely the "super panels" which form the 747 fuselage. These consist of two or more panel assemblies that join together and are mated to frames to form even bigger assemblies. These large sections are shipped, generally by rail, to Everett for final assembly.
The precise manufacturing of the new panels reduced the enormous variability inherent in the manufacturing of such large pieces and cut down on the hugely expensive rework of panels to make them fit once they had arrived at Everett. The variability was largely caused not only by the sheer size of some of the parts, but also by the wear and tear on the ageing manufacturing jigs at Northrop Grumman's Hawthorne plant in California.
Northrop Grumman, which produces around 25,000 parts for each 747, signed a strategic alliance with Boeing over the AFA proposal in late 1994. In April 1997 it delivered the first parts produced using the new process. Boeing, meanwhile, also began to plan ways of taking advantage of the new method. Rodger Riggers, Boeing's FAIT programme manager since the start of the effort, recalls that "after the AFA implementation, Northrop Grumman said to Everett: 'Now what are you going to do?' That's how FAIT was born."
The FAIT concept was developed in the third quarter of 1995 and built entirely on the benefits of the CATIA-based AFA process at Hawthorne. Boeing took advantage of the precise manufacturing of the super panels to ditch its own ageing assembly and manufacturing tooling. It simplified the way the aircraft could be put together by minimising the variation in the size of parts and the location and size of holes. Precision "golden holes", located every 50cm (20in), were suddenly available to "self-locate" the panels to each other. This process, known as determinate assembly, uses part-to-part indexing, rather than the conventional part-to-tool indexing system used in the past.
Changing old ways
A vital element of the switch to the new process was the gradual change-over from the old to the new. A three-phase programme was started, with the AFA hardware arriving slightly before the implementation of the new tooling at Boeing. Under Phase I, the early drawings were digitised by the third quarter of 1996. Northrop Grumman delivered the first Section 42 AFA section in early April 1997, followed two weeks later by the first Section 44.
With Phase II under way, the first of the larger aft Section 46 panels arrived in May 1997. The first aircraft to incorporate an AFA-built Section 44 panel began rolling down the line last October, with implementation the same month of the first FAIT tooling at Everett under Phase III. Section 42 improvements were instituted over six months at the end of last year and the start of this.
Section 46 hardware began arriving in April and loading into the new tooling in July. Aircraft incorporating some sections made using the advanced AFA/FAIT processes have therefore been in service since early this year, but the JAL aircraft will be the first to have an all-AFA/FAIT fuselage.
In concert with the changes being made to the bulk of the fuselage, the assembly and tooling for the tail Section 48 (built by Northrop Grumman in Texas) and the conventionally made nose Section 41 (built by Boeing Wichita) were revised to take advantage of the new process. Although the tail unit is "not really part of FAIT, we saw some synergies", says Riggers. Two major areas of the fuselage, therefore, the forward and aft sections, use the benefits of AFA/FAIT even though the tip of the tail and the nose sections have not been digitised.
Changes in the flow sequencing have been made as a result. The Section 41/42 and 46/48 joins have been moved back from the final body assembly area to the body section assembly area. "Under the old process, we built them individually and then sent them to seal and test. Then we brought them back and joined them and installed them before passing them to final body join. Under the new process, we are moving the 41/42 join and 46/48 join back to structures. We then paint and seal them before bringing them back to have systems installed. There have been difficulties and things we've had to learn, but we have seen great strides already," says Riggers. The new assembly process ensures commonality of work packages, says Boeing, which adds that it is more adaptable to "lean" manufacturing principles. A study is also under way to evaluate the possible digitising of Section 41.
Another benefit is dramatically reduced variability between tooling requirements for passenger -400s and freighter versions, which still have the original -200F-style upper deck. The new process adaptability means that "there is not so significant a difference", says Riggers, who adds that the benefit is particularly opportune, given that almost half of the expected 24 aircraft to be built next year will be -400Fs.
Because of the changes, assembly workers have had to familiarise themselves with entirely new processes. "A big part of the change to the process involved locating the panels, using the digital dataset and ensuring they were in place with two kinds of lasers," says Riggers. The "planising" laser is used initially to set the panels in place, using targets set on the parts themselves. The position of the panel targets is then assessed against reference targets located in known, fixed spots on the tooling.
"We have feedback on where we are in real time for configuring the panels," adds Riggers. "Then, afterwards, we do an autopsy and fire conformal shots using a laser tracker." A computer compares the panel position against the reference position in the database to guarantee correct positioning.
Adjustable support struts called "pogos" are used to position the structure in the vertical plane. The maindeck floor of the sections rests on a set of teflon rollers to help adjust the horizontal position. Panels are held in place by motor-driven manipulators that can be controlled with a hand-held joystick. To ensure that the large panels of some sections do not begin to spread under their own weight during assembly, Boeing has also installed adjustable jib cranes. These attach tension lines to the panels and can be used to make minute adjustments to ensure a proper fit.
The early results indicate that Boeing and Northrop Grumman's multi-million dollar investment is starting to pay off, although recent cost-overruns reported on AFA by Northrop Grumman, caused by rate change adjustments, means that break-even could be further off than planned. The overall Boeing investment in the project is estimated at around $400 million. The company says officially: "By doing this, we are making a huge commitment to the future of the 747," a claim it backs up by pointing to the space allocated for the tooling that would enable it to take sections for any proposed stretch version.
In other areas, the benefits are accruing in terms of higher quality and reduced rework. Frame and skin panel mismatching was a constant headache for Everett workers, who often spent days adjusting gaps and adding shims to bring parts into line. Initial analysis indicates that skin panel mismatching is improving by a factor of around 4:1, with the resulting reduction of rework by the same magnitude. "Around 99.73% of the time there is almost perfect tolerance versus the former system, under which it would be out of spec around 33% of the time," says Riggers, who adds: "Another big saving to us is simply maintaining the tools. Every few aircraft we had to overhaul the tools. Now all we have to do is take a few laser shots."
For the future, Boeing is studying digitising the wing, should the root-insert stretch version be developed. In the meantime, the changes ensure that the assembly and manufacture of the baseline 747 is in line with that of the 767 and 777 and that the 30-year-old design gets a new boost of life into the 21st century.
Source: Flight International
