A riveting need

German engineers trial gun with a difference, that incorporates automatic 3D quality checking technology to make safety process even faster. Stuart Nathan reports.

Aircraft — particularly passenger planes — use increasingly advanced technologies, but they are largely held together by good old rivets. Hundreds of thousands of them.

Checking the integrity of a riveted joint is crucial, and is still generally a manual operation. Now, however, Airbus Deutschland is working with the Fraunhofer Institute for Factory Operation and Automation to incorporate automatic rivet checking into the riveting operation itself.

To check a rivet, test engineers look at the rivet head to make sure it isn’t scratched, and run their thumb over the joint to check how far each rivet protrudes from the surface. Particularly critical joints are checked using a dial gauge.

This type of inspection is thorough and reliable, but it’s also very time-consuming. What’s more, because the checks are made after all the joints have been riveted, a malfunctioning riveting machine might make many hundreds of defective joints before the problem is discovered.

The Fraunhofer team, based in Magdeburg, aims to develop a new type of riveting gun to check the quality of each rivet as it’s fired into the panels. The device uses a 3D inspection method, OptoInspect, which tracks the shape of the rivet in the joint and detects defects, but does not increase the time needed for the riveting cycle.

After the joint has been riveted, the device projects a pattern of 18 strips of light on to the rivet head, and this is recorded on camera. A machine vision system derives a 3D cloud of measuring points from the distortions of the stripe pattern as it falls on to the head, which allows the system to measure how far the head is protruding from the panel surface, and to detect whether the head is at an angle.

This information is relayed to the riveter, who can decide whether a defective joint is a one-off, or whether it’s likely to recur. If a chip caught in the drill is likely to lead to a series of defective rivets, or if a worn tool needs replacing, the equipment can be shut down and fixed, or replaced.

The entire measuring process takes around a second, the team claims, which is vital with such a fast process. ‘Since a joint is riveted every 4.5 seconds, one of the main tasks when developing the system was to ensure that data was recorded quickly to monitor quality,’ explained research leader Dirk Berndt. ‘In such circumstances, optical inspection techniques were the only viable option.’

Airbus Deutschland is currently testing the system at its Nordenham plant, which manufactures fuselage shells for the Airbus airliner families. If the system stands up to the rigours of day-to-day production, the company plans to integrate it into its existing riveting machines.