Because orbital drilling allows for drilling and finishing in a single operation, a fully implemented process can reduce drilling time by 50% over conventional methods, according to Novator. The need to disassemble the parts to remove burrs is eliminated.
To exploit the advantages of orbital drilling, Airbus started a project with Novator a few years ago in order to develop a portable orbital drilling unit for final assembly lines in Toulouse, France, and Hamburg, Germany. Called Twinspin PX3, the CNC-controlled unit allows for a continuous radial offset adjustment of the cutting tool. It can produce not only cylindrical, but also conical and other complex-shaped holes.
In addition, an ID chip reader for position control and automatic diameter and parameter settings is included in the unit. The ID chip reader can also be used to identify a specific predetermined hole drilling recipe to perform adaptive stack drilling (parameters can be changed when moving from layer to layer in a material stack).
By working in close cooperation with Novator, Airbus has been able to thoroughly specify all requirements of the system to qualify and use it in a production environment. Intensive tests have been performed at Airbus to validate the industrial capability of the system for the A320 family final assembly lines, and the aircraft maker has decided to fully deploy it on all wing-to-body stations. With the switch to the Novator unit, the need for five currently used machines is eliminated.
Orbital drilling is based on machining material both axially and radially by rotating the cutting tool about its own axis as well as eccentrically about a principal axis while feeding the tool through the material at low thrust force. The small chips that are produced can be removed easily by vacuum. Efficient chip removal prevents heat buildup and eliminates the risk for matrix melting in composite materials and heat-affected zones in metals. In addition, it eliminates the risk for chip-induced damage and makes cleaning of structures obsolete.
The tool only intermittently contacts the material, which allows for efficient cooling and makes dry drilling possible. It also increases the tool life in dry drilling. Dry drilling is highly desirable as it reduces cost and has little environmental impact (vs. the use of coolant). In some applications, however, minimal-quantity lubrication is required to reduce friction between the cutting tool and the workpiece to reduce cutter wear.
Low thrust force allows for burr-less drilling in metals and delamination-free drilling in laminated composite material. It also minimizes the risk for part deflection when drilling in thin structures and it facilitates use of automation such as industrial robots, which are force-sensitive.
This article is based on SAE technical paper 2007-01-3849 by Benoît Marguet, Frédéric Wiegert, and Olivier Lebahar of Airbus France; Bertrand Bretagnol of Assystem; Fahri Okcu of Airbus Germany; and Eriksson Ingvar of Novator.