Making a Splash! - Rexroth Ball Rails Plunge into First Underwater Application for Aircraft Part Inspection

Underwater inspection of aircraft landing gear using ultrasound may be fairly common within the aircraft industry, but this type of inspection recently took Rexroth Ball Rails on an extremely uncommon journey. That journey led inside an immersion basin used by an aircraft parts inspector—an environment comprised solely of water.

The idea to use Ball Rails in this application was the brainchild of Mecnov, Inc., a Quebec, Canada-based original equipment manufacturer specializing in material handling equipment. Kennedy Gagnon, Mecnov technical manager, explains that in order to conduct non-destructive inspection of aircraft landing gear in an immersion basin, inspectors first submerge the forged titanium part in the basin. The landing gear forging comprises a structural part made of a titanium pipe or cylinder shaped like a tree trunk with a branch cut. The cylinder area of the part measures from 150mm to 180mm, while the overall part measures from 300mm to 700mm with a weight of 100kg to 600kg.

The operator uses non-destructive ultrasound within the immersion basin to look for inclusions or defects in the forging.

Next, the operator uses nondestructive ultrasound, which, like an x-ray, freely travels to the part using the water as its conductor. The inspector then looks for inclusions or defects in the forging amplified with the ultrasound. This amplification allows the inspector to identify inclusions in the early stages of the manufacturing process before the forging is further shaped into a finished product. During each inspection, information about the part is stored in the machine for later review, at which time the operator can determine whether to accept, reject, or repair the part. "We chose Rexroth Ball Rails for the submersed portion of this unusual application based on our success with the product in other applications," says Gagnon. "We noticed that when splashed with water from a nearby process, a competitor's rail quickly began corroding, which led us to investigate Rexroth Ball Rails and ultimately to switch to Rexroth."

MKR linear module for demanding speed and load requirements.

Later, for an Asiatic client, Mecnov was tasked with developing a system able to inspect the titanium forgings completely submerged in water. "In addition to the underwater aspects of the process, one of our biggest challenges was to design a part rotator able to accommodate parts of different sizes and weights as well as a way of loading and unloading the parts," says Gagnon. When the immersion basin application presented itself, Mecnov contacted Michael Beaudry from Bosch Rexroth Canada in Montreal to discuss the possibility of completely immersing the Ball Rail in the basin.

"We had a sample of the Rexroth Ball Rail and tested it by immersing it in water for one week," says Gagnon. "When the product showed no signs of corrosion after one week, we decided to try the rail in the immersion tank."

The Ball Rails and blocks are used within a high precision mechanism in the immersion basin to axially adjust a mobile, nonmotorized spindle point, allowing easy loading and part holding during inspection. Because the landing gear part is in an early stage of the process and has just been forged, the "raw" nature of the titanium adds pollutants to the water in the test basin. So, the performance of the Ball Rail is additionally impressive because of the contaminated nature of the water in which it resides.

The Rexroth Ball Rail remains in good condition after two years of continuous immersion and operation in the basin.

"This was the first time Rexroth Ball Rails were used under water," notes Gagnon, "and the results far surpassed our expectations." According to Gagnon, the immersed Rexroth Ball Rail is still in good condition after two years of continuous immersion and operation.

In addition to the submersed Ball Rail, Mecnov uses MKR and CKK linear modules with 25mm blocks on the top of the machine as part of a 5-axis Cartesian robot to position the ultrasound probe around the part being inspected.