Quick fix

GKN Aerospace and German company SLCR (Selective Laser Coating Removal) are developing a novel automated laser process that prepares the surface of damaged composite aircraft parts ready for repair.

From bird impact through to runway vehicle accidents and dropped tools, composite bodywork on aircraft faces damage through a variety of causes, and every day an aircraft or component is out of work costs the airline money. Repairs to this kind of damage form a significant part of GKN’s £160m MRO (maintenance, repair and operating equipment) business.

Preparing a surface for repair is a highly skilled, time-consuming manual process, using fine abrasives that can create hazardous dust particles, which have to be cleaned off using solvents. In the new system, the laser, which covers a broad area and is tolerant of being placed varying distances from the target, evaporates only the organic glue that bonds the composite from the surface.

Phil Grainger, senior technical director and chief technologist at GKN Aerospace, explained: ‘It is self-limiting in that it will only take away the layer of organic material that it can see. As the light hits the surface, anything that’s behind something else is shrouded and can’t be damaged.

‘The reason we’re so interested in it is that for many of our applications where we currently use a manual method we only have 0.1mm of tolerance. We need a system that is as good as this, and a laser is the only system available today that can do that.’

GKN Aerospace estimates that using the new system technicians can carry out a repair in a third of the time a manual repair takes, and with a 60 per cent cost reduction. A typical repair for a flap takes one person two weeks, including carefully rubbing one layer of composite glue at a time before putting the repair patches in. SLCR’s technology carried out the same preparation step on a test coupon in around one hour.

‘The repair process also includes the restoration, repair, the re-curing and so on, but preparing the repair surface could be very quick indeed, and so reduce the total repair process by a third,’ said Grainger.

After three years working on the project, SLCR was successful in getting approval for the process from Airbus at the end of last year, and it also has approval from Boeing for the process, subject to meeting certain American regulations.

‘If Airbus and Boeing allow use of the process on the aircraft, we will seek to expand the Airbus approval and get overall approval by applying this technique to everybody’s aircraft and engine parts,’ added Grainger.

BAE Systems is also considering adopting the process for military aircraft and has shown interest in joining GKN in this venture, he said.

SLCR already has an Airbus-approved production system, which is used to either prepare units such as rudders and tail units for painting, or to evaporate off the organic paint from painted units. The company is preparing to market a system that will de-paint whole aircraft when they are in for maintenance. A KUKA Omni-move robot holds the laser head, and the machine can be programmed to automatically remove one layer of paint or primer at a time down to the organic adhesive on top of the composites.

Under GKN and SLCR’s technology agreement, the companies aim to have a demonstration machine built in two years, but Grainger said they’d like to push that forward and have it done by the end of 2010. ‘That will be an application machine, but not a full production machine,’ he added. ‘The final machine will have optical sensing and will be CNC controllable so it can learn to do the job.’

The programme has funding from ELF (Environmental Lightweight Fan), the exclusive agreement between GKN and Rolls-Royce to develop composite fan blades for Rolls-Royce engines.

‘Those parts are micro-engineered, and each laminate is about 1/5,000 of an inch thick, so it will particularly benefit from this repair technology,’ said Grainger.