BEST QUALITY: RIVET BY RIVET

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BEST QUALITY: RIVET BY RIVET
28 December 2006 - Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.

Take a close-up look at an aircraft and you soon realize what holds it together, rivets. Several hundred thousand metal rivets go into every passenger aircraft. The riveted joints are subjected to enormous forces. A new quality shows defects during production.

Riveted joints used to be inspected manually. Test engineers would make sure the rivet head was not scratched and run their thumb over the rivets to check how far each rivet protrudes. Critical joints were also checked using a dial gauge. Yet this manual check is time-consuming. Depending on the size of the aircraft, the test engineers need anything between an hour and a couple of hours to inspect the riveted joints on the fuselage. This downstream quality check has another disadvantage: Say a chip caught in the drill causes a defect, then up to 150 defective metal rivets might be fitted before the problem comes to light.

Engineers from the Fraunhofer Institute for Factory Operation and Automation IFF are working together with Airbus Deutschland GmbH on an automated inspection system. Their aim is to integrate the system into the riveting machines so that defects can be uncovered during production. "Since a joint is riveted every 4.5 seconds, one of the main tasks when developing the system was to ensure data was recorded quickly to monitor quality. In such circumstances, optical inspection techniques were the only viable option", explains Dirk Berndt of the IFF in Magdeburg. Other requirements meant that the system had to carry out a full inspection, provide reliable feedback on existing defects, be easy to use and interface with existing process control systems. And all that without adding substantially to the riveting cycle.

To meet these varied requirements, the scientists have come up with a sophisticated inspection concept, “OptoInspect” for three-dimensional rivet measurement. Once a joint has been riveted, a pattern of 18 strips of light is projected onto the rivet head and recorded by a camera. A three-dimensional cloud of measuring points is calculated from the stripe pattern. The rivet head protrusion and the tilt angle can then be determined from this data. If a riveted joint is defective, the riveting machine operator has all the necessary information to decide whether it is a one-off defect or whether the equipment needs to be shut down immediately, to remove a chip caught in the drill or replace a worn tool. Again the measurement process takes just a second. The inspection process is currently being tested at the Airbus plant in Nordenham. If the system manages to withstand the rigors of daily series production, it will be integrated into the existing riveting machines.

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About: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
The Fraunhofer-Gesellschaft undertakes applied research of direct utility to private and public enterprise and of wide benefit to society. Its services are solicited by customers and contractual partners in industry, the service sector and public administration. The Fraunhofer-Gesellschaft maintains over 80 research units at more than 40 different locations throughout Germany. A staff of some 12,700, predominantly qualified scientists and engineers, works with an annual research budget of over one billion euros. Of this sum, more than € 900 million is generated through contract research. Two thirds of the Fraunhofer-Gesellschaft’s contract research revenue is derived from contracts with industry and from publicly financed research projects. The remaining one third is contributed by the German federal and Länder governments, as a means of enabling the institutes to pursue more fundamental research in areas that are likely to become relevant to industry and society in five or ten years’ time.

The Fraunhofer-Gesellschaft is also active on an international level: Affiliated research centers and representative offices in Europe, the USA and Asia provide contact with the regions of greatest importance to present and future scientific progress and economic development.

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