Engineers at The Boeing Company's Auburn, WA, Fabrication Division plant achieved a big reduction in setup times and increased productivity using a universal clamping system to fixture airframe components.

In one operation, fixture change time on a large gantry for airplane flaps was cut from nearly two hours to 20 minutes. Another changeover for smaller parts (trunnions) that used to take an hour is now completed in seconds using the Unilock universal clamping system from BIG Kaiser Precision Tooling (Elk Grove Village, IL).

At Auburn, a series of Unilock clamping chucks mate with a series of clamping knobs to hold the fixture or workpiece. Each chuck can provide up to 11,240 lb (50 kN) of clamping force and achieves repeatability of 0.0002" (0.005 mm) or better. The system provides a solution for two tough setup problems: repeatability of location from one fixture or workpiece blank to another and transfer of work from one machine tool to another.

A Unilock demonstration impressed Boeing engineers with the system's speed, repeatability, accuracy, and ease of use. Even more important, Boeing retained the ability to build its own fixtures and mating receivers with standard Unilock components.

The modular system adapts to workpieces of virtually any shape or size. Zero point clamping chucks are available in different configurations for use with mills, lathes, grinders, and EDM machines, as well as measuring equipment such as CMMs. Standard pallets come in steel and aluminum, or customers can produce their own pallets by purchasing the positioning components. Position and clamping elements can also be mounted directly to workpieces or existing fixtures.

In one operation, Boeing is using the system to hold flaps for the 777 commercial airliner during machining. The operation involves machining separate flap halves, then fastening them together. "It used to take us two hours to change out the fixtures," says process engineer Steve Martin. "With the Unilock, we just clean off the fixtures and put them back on the machine. It takes about 20 minutes."

Another operation involves machining trunnions for the 757. "The parts require seven different media for roughing, finishing, and other operations. We flip parts over to work on both sides and use several different tools. Unilock always works. The center locator is precision-ground and uses a diamond pin. We know that's where it's going to be every time," says Boeing NC programming manager Miles Olson.

"We have long run times on these parts--anywhere from 45 minutes to four hours," Olson continues. "We have six fixture changeouts per shift. Unilock has cut our clamp and unclamp time, but it's not just the speed that makes a difference. It's accuracy and repeatability. When we clamp the fixture, we're done. We hit cycle start and cut the part, knowing we are getting accurately machined parts with side A and side B matching precisely."

Boeing is using a Unilock riser plate to hold fixtures on a five-axis Makino machining center. Engineers conducted a test that involved lifting the fixture off the riser plate, then reclamping and cycling it back into the machine. "We achieved a simultaneous nesting surface for the fixture to the riser surface and Unilock chucks within 0.0002" [0.005 mm]," Olson reports. "Tooling pin locations on the first fixture probed within 0.0002" on the first check.

"We have reduced fixture clamp and unclamp time for this pallet to zero," he adds. "It also eliminates the need to re-adjust the fixture location on the pallet to get it within our fixture probing tolerance. Fixture locating accuracy and repeatability are now under control."

Boeing typically performs multiple operations--turning, milling, and grinding, for example--on the same workpiece, using several different machine tools. Typical tolerances are plus or minus a tenth or two, according to Olson and Martin. Boeing needed a central datum for transfer of a single workpiece from operation to operation and machine to machine.

With Unilock, a workpiece reference location need only be established once. Alignment is from the chuck centerline, and the location data are captured electronically and kept in the machine's CNC. Engineers can run any fixture at any time, giving Boeing a universal system for use throughout the shop.

"Operations that used to take days are now completed in minutes or hours. The system gives us much more versatility to make our commitments," Olson says.