Wing assembly for the world's largest commercial aircraft, the A380 from Airbus (Toulouse, France), occurs in two phases. First, large aluminum-alloy wing panels that make up the "skin" of the structure are fabricated and joined to stringers, which provide strength and aerodynamic curvature. These wing panels-10 per wing-are then joined to an internal wing structure made up of spars running the length of the wing and ribs crossing from the leading to the trailing edge.

The sheer size of the wings makes their assembly an engineering challenge: Each wing is almost 120 feet long, creating a total surface area of 9,100 square feet. Their assembly includes the drilling of tens of thousands of precisely positioned holes to receive the requisite fasteners.

To speed up the process and ensure that the fasteners are installed correctly, Electroimpact (Mukilteo, WA), under contract to the Airbus wing construction facility in Broughton, UK, set out to automate as much of the process as possible. This, in turn, required the use of dozens of precise hydraulic and linear-motion subsystems, as well as powerful motion control.

In the past, wing panel assemblies were built on manual jigs, requiring many skilled workers to locate and drill holes, pull components apart for deburring and cleaning, apply sealant and insert two-piece lockbolt fasteners. The assemblies were then transported to a riveting machine for final rivet installation. Production rates were limited by the number of jigs in production, worker access and speed, and hole quality and rework requirements. Finished panel quality was also limited by how well the fixture held the components in correct contour.

To assemble wing panels for the A380, Electroimpact built four machine lines, each of which has a number of jigs to hold the skin and rib pieces in place while an automated, custom-built E4380 machine drills, rivets and bolts them together. Sealant is applied to the components during the jig load, and no temporary fasteners are used.

The machines can install rivets and bolts ranging in diameter from 0.25 to 0.5 inch, with a stack range up to 2.5 inches. Automated cold working, hole probing, countersink sealing and collar installation are all included.

To achieve the necessary positional accuracy, Electroimpact's machines and fixtures incorporate dozens of linear guides and ballscrews from Bosch Rexroth Corp. (Hoffman Estates, IL). These include preloaded roller-runner blocks, and preloaded ground ballscrews and caged-ball runner blocks to ensure rigidity in the system.

"At this stage, speed, accuracy and operator safety are critical to this success," says Electroimpact mechanical engineer Ben Hempstead. "The goal was not just to design machinery that automates manual tasks, but also to improve quality and reduce process time."

After the wing panels are complete, they must be moved to wing-structure jigs where they are fastened to the underlying structural framework. Because of its size, the largest of the panels, which is approximately 111 feet long and weighs 8,818 pounds, cannot be moved by crane lift-doing so would cause the panel to twist and bend. Therefore, Electroimpact decided to move the panel using six coordinated servo hydraulic arms that engage the panel along its entire length. This panel manipulation system uses a Rexroth HNC 100 servo hydraulic controller, which provides fine position control with seamless transition between position and force control.

"Two of the six arms control the vertical position of the panel," says Electroimpact project engineer Ted Karagias. "The other four arms act as slaves imparting a constant programmed force upon the wing panel. That way, when the positioning arms are commanded to move either up or down, the load-seeking arms follow along to maintain the panel's form."

Once in the wing structure jig, the wing panels are fastened to the internal rib and spar structure both manually and with Electroimpact's horizontal automated wing drilling equipment (HAWDE), a kind of transportable, 7,000-pound CNC drilling machine.

The HAWDE system uses a square rail guideway and a gear rack for movement along the X axis. All other axes use traditional linear and rotational bearings. To reach difficult areas the machine performs a "Y-shift," whereby it extends above its normal position about 3 feet using a sturdy size 45 Rexroth roller rail system.

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