Laser tracker speeds aircraft assembly

Manufacturing Engineering, Nov 2002

Lockheed Martin Aerospace is showcasing multiple new technologies in development of its Joint Strike Fighter (JSF) for the US Air Force.

Case in point: an LTD500 laserbased industrial measurement system from Leica Geosystems (Norcross GA). Lockheed uses the device at its Ft. Worth, TX, Airframe Affordability Demonstration (AAD) site in conjunction with an engineered jacking system to execute a JSF final aircraft mate demonstration. Able to perform up to 1000 measurements per second and with a 70-m diam measurement volume, the laser system is also used to set up, measure, and inspect assembly tooling details based on CAD models.

Manufacturing engineer Rina Molari is responsible for gathering and analyzing data collected by the instrument. During the demonstration, Molari drives the tracker's laser beam and target ball out to each of six checkpoints, which are small circular slots designed into the tool for this application. After a reading, she adjusts the jack system and watches the laser tracker feedback coordinates until the components are aligned. The aft fuselage then slides easily into position for connection.

This type of mate concept has been done on earlier programs, but required control tools and gages to maintain very close tolerances. Those tools were shipped all around the world to wherever the aircraft were built.

"On the JSF, we eliminate the control tools and gages through the use of digital data, and by having processes and machines that can meet this level of tolerances," explains Chet Burge, JSF Airframe Mate and Delivery Integrated Product Team Lead. "The laser tracking allows us to validate our designs and close-tolerance work on the JSE 3D CAD, the Internet, going directly to NC, and the laser tracking systems all create a strategic loop for precision in the JSF program."

When compared to the F-16 and other aircraft mating systems, the JSF mating process is a quantum leap. Today it takes about 8-10 days to mate the aft fuselage with the center fuselage of an F-16. A simple mate joint design, coupled with the laser tracker and the innovative jack system, is expected to cut the JSF mating cycle to about 20 hours.

The process will enjoy further time savings once the operation is automated. With Leica's patented absolute distance meter (ADM), the laser tracker can be pre-programmed for pointand-shoot measuring and will search out the coordinates. The tracker laser beam will be shooting toward each target, waiting for the operator to put the target into the checkpoint hole. The ADM allows the operator to move around the area freely, and if a beam is broken, it can be retrieved at its last location.

The JSF program also incorporates another primary laser tracking application. When assembling the tools, Lockheed workers track a locating point over the life of the tool to see if there are any variations. Using the laser tracker, they set up 3D coordinate points in space and verify them initially and on an ongoing basis.

"With the tight tolerances we are trying to maintain for this program, you have got to be able to fabricate and validate a tool quickly and accurately," says Burge. Use of the laser tracker helps us achieve a 90% reduction in tools." Circle 225