An electromagnetic dent-removal (EDR) process used by McDonnell Douglas Aerospace (MDA) is being offered to outside users following its formal certification as an approved repair process for the MD-90.

EDR has been under development at MDA since 1986, and used on commercial and military production lines to undertake pre-delivery dent removal.

The company estimates that repairing instead of scrapping parts such as leading edges and flaps using EDR technology saved around $14 million during 1993.

The system works by conducting electromagnetic fields across the inner and outer surfaces of the damaged areas during a two-phase process, using a hand-held flux- concentrator coil. During the first phase, called a slow-bank action, the electromagnetic field is generated by discharging a capacitor through the concentrator coil. This puts a field at the front and rear of the dented surface.

The second phase involves a second capacitor discharge, which causes the instantaneous collapse of the magnetic field at the front of the dent. When the field collapses, the magnetic field at the back of the dent creates a force, which pushes the metal towards the concentrator coil from the inside out. By holding the coil against the surface, the operator prevents the metal from bulging outwards.

Demonstrations have been given to Beech, Cessna, Dassault and Gulfstream. Around 14 corporate aircraft have been repaired since the beginning of the year.

Made in Seattle, Washington, by Electroimpact, EDR is operated by MDA under licence.

Providing an example of potential savings claimed by MDA, Jack Cotter of the company's engineering technology says that a dented slat for a Dassault Falcon valued at $75,000 and costing "...between $20,000 and $25,000 to pull out and re-skin and repair, can be repaired for less than $5,000 using this technique".

The portable ERS system can be used to repair flight ramp dents without removing the part from a fully fuelled aircraft, or taking off the paint. It can be used on single-sheet aluminium and bonded-aluminium honeycomb surfaces. Repaired surfaces retain "at least 90% of their original strength", says the company.

Source: Flight International