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Long Line in Long Beach PUBLIC ACCESS

A Giant Riveter at Boeing Sews Fuselage Panels Together for the Air Force's Equally Large C-17 Cargo Transport.

[+] Author Notes

Associate Editor

Mechanical Engineering 121(10), 82-83 (Oct 01, 1999) (2 pages) doi:10.1115/1.1999-OCT-8

This article discusses various aspects of a riveter and its usage at Boeing. Boeing took delivery of the riveter in 1998 from the German company Brötje Automation and the Spanish company Torres Industries. The riveter puts together the fuselage panels of the U.S. Air Force's C- 17 Globemaster Ill, a giant military transport aircraft {CE: Please check the validity of this edit.}. In four stations, the riveter joins panels to panels, and panels to frames. At the first station, an overhead crane takes an individual panel out of a shipping container, rotates it from a vertical posture to a horizontal one, and then lowers it onto a field of spike-like ‘pogos.’ The pogos extend and retract radially from a bridge, cradling a panel by conforming to its contours like a waiter balancing a tray on the tips of all five fingers. Adding to the already complex matrix of rivet data and locations is the control of every pogo and bridge move for any given panel assembly. With nine pogos per bridge, each with radial and circumferential locations, and five bridges per car, each of which must move along the length of the shuttle for tool clearance, the machine presents a monumental programming task.

Visitors to New York City seldom realize that they are passing one of the world's tallest skyscrapers when they walk alongside the Empire State Building. The tower rises in steps, so the pedestrian who gazes upward never sees an unbroken vertical expanse of concrete and glass. Anyone actually looking for the place needs to keep an eye out for signs at entrances that seem only to whisper its name.

There is no such sign proclaiming "world's largest riveter" hanging on Building 52 at the Boeing plant in Long Beach, Calif. , either. But, then again, it probably doesn't need one. Standing beside this behemoth, you 'd have to wonder how it could be anything but.

Large does not necessarily mean complex, although in this case, it did. Teaching the machine to assemble parts at the Boeing plant took the help of robot simulation software and many hours of programming.

Boeing took delivery of the riveter in 1998 from the German company Brötje Automation and the Spanish company Torres Industries. Months after senior Boeing manager John Deitenbeck and a team of mechanics, quality engineers, and production personnel accepted the machine in Europe, the sea containers began arriving at the Port of Los Angeles . As weeks passed, they kept coming.

In March 1998, Boeing began installing the riveter. Production started in July. Fully prepared to ruin the first part they ran, as the engineers at the Boeing plant in Wichita, Kan. (which owns four similar, smaller units), had warned them they might, the Long Beach engineers managed to inflict upon it "only a couple of bumps," said Dietenbeck. At a cost of a quarter of a million dollars apiece, even their very first part was a success.

The riveter puts together the fuselage panels of the U.S. Air Force's C-17 Globemaster III, a giant in its own right. In four stations, the riveter joins panels to panels, and panels to frames. Three shuttle cars transfer the assemblies between stations. At the first station, an overhead crane takes an individual panel out of a shipping container, rotates it from a vertical posture to a horizontal one, then lowers it onto a field of spike-like "pogos." A vacuum cup tops the end of every pogo.

The pogos extend and retract radially from a bridge, cradling a panel by conforming to its contours like a waiter balancing a tray on the tips of all five fingers. Pogos can move along the circumference of the bridge as well. The bridges, five of which compose a shuttle car, can move axially. Flexibility designed into the pogos lets them accommodate a wide variety of panel shapes without needing dedicated tooling.

Longerons and Tear Strips

Coming out of the container, each panel consists of a 0.060- to 0.200-inch-thick outer skin, a series of longitudinal stringers, or "longerons," that have been riveted to the outer skin, rows of radial tear strips (which stop the outer skin from ripping in the event it is punctured), and an array of L- and T-shaped sh ear clips that have been riveted to the longerons.

After placing the first panel, the crane grabs and places a second panel, and many times a third one. The pogos hold the panels within 0.090 inch of one another. Here, at the first station, workers temporarily stake J-shaped longerons between the panels. These longerons hold the panels together until they are spliced in the operation that follows.

Station No. 2 splices the panels together. Here, a ring riveter with dual robots joins the panels in a process that Boeing calls "seam sew-up." One robot flits around above the panel, while a second robot works in unison with the first from below. The upper robot drills and countersinks the panel. Then, with the lower robot serving as an anvil, together the two robots install a rivet. This dance repeats a thousand times or more for every assembly.

A butt splice joins one panel to its neighbor. Six rows of rivets, 3/4 to 1 inch apart, make the splice, sandwiching between them a J-shaped longeron, a doubler, some sealant, the outer skins, and a "beauty strip," which covers the gap between adjacent panels.

At station No. 3, workers temporarily attach frames to the panels, securing them to several prepiloted shear clips. The frames run perpendicularly to the longerons, and nest up between them.

At the fourth and final station, the frames are permanently riveted to the shear clips. Another robot- working alone this time-gets up around either side of a frame, where it drills and countersinks a hole, then inserts and squeezes a rivet. The robot repeats the sequence a hundred times or so for every panel assembly.

Spanning 300 feet of floor space, the automatic line in Long Beach dwarfs a stepladder. The frame riveter (in the foreground) has a panel in place. So does the ring riveter, which is farther back.

Grahic Jump LocationSpanning 300 feet of floor space, the automatic line in Long Beach dwarfs a stepladder. The frame riveter (in the foreground) has a panel in place. So does the ring riveter, which is farther back.

Upon leaving the riveter, the assembled panels move to an intermediate-assembly building, where they link up to become the forward, center, and aft tubes of the aircraft. To make one C-17, the riveter must convert 29 individual panels into 11 panel assemblies. The biggest of these assemblies measures 25 feet wide by 41 feet long.

The new machine increases riveting productivity more than tenfold, according to Robert Dale, a Boeing numerical control programming manager for the C-17 program. Compare six to eight fasteners a minute by the Brötje machine to one fastener every two minutes by hand . Besides speed , the automated riveter delivers a better job than did former manual methods, and avoids costly rework.

Of course, the rivets are not all identical. They vary by size and style. To keep track of all possibilities, Boeing groups like fasteners by layers in a CAD file. Complicating matters, each spot on a panel that gets a rivet has coordinates and attributes identifying rivet placement and type. All this information would be difficult enough to keep straight by someone riveting by hand. The problem is no less daunting for the machine.

Adding to the already complex matrix of rivet data and locations is the control of every pogo and bridge move for any given panel assembly. With nine pogos per bridge, each with radial and circumferential locations, and five bridges per car, each of which must move along the length of the shuttle for tool clearance, the machine presents a monumental programming task. There really isn't any good way to test programs on the machine using the expensive panels themselves. For this reason, off-line robotic simulation software mimics the Brötje first.

Starting from 3-D geometries of panels that have been designed on the Boeing CAD/CAM system. (from Unigraphics Solutions Inc. in St. Louis), the company's NC programmers retrieve data on fastener type and location. Then, they program fastener type, approach and retract motions, and tool selection for every hole to be drilled and each rivet to be inserted. Macros eliminate some repetitive tasks. Working with a single CAD layer of like fasteners, for example, programmers call up an offline processing system to interrogate the fastener attributes file, which then determines what machine function codes to write in the program.

Programming a typical assembly of two or three panels takes about 300 hours. "Without offline robotic simulation, programming the many panels would be inconceivable; at the very least, it could take years," Dale said. Simulations, because of their massive file sizes, run for approximately 16 hours.

Deneb Robotics of Troy, Mich., supplied Igrip simulation software to Brötje and supported program development for the riveter from its office in Germany. Boeing secured a license for Igrip software to continue the task of programming the Brötje machine for most of the

C-17's panels. This effort continues today. Some panel assemblies, such as those that make up the fuselage ends, are too complex to be riveted automatically. The riveting of these few pieces will likely remain a manual process.

Simulation saves the NC people worry over holes either going undrilled or getting stuffed with too many rivets. It also alleviates concern about crashing the robots into the machine or into the panels. Of course, simulation is practical only up to a certain resolution; beyond that, the programmer s still like to get out to Building 52 and ride the riveter. That way, they know for sure that their freshly coded programs aren't running the riveter ragged.

Copyright © 1999 by ASME
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