Europe investigating new aerospace press-forming possibilities

  • 04-Aug-2008 04:00 EDT
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A multipoint forming (MPF) prototype unit was built at Jilin University in China.

DATAFORM, a project granted by the European Commission within the 6th Framework Programme, is developing what it says is an accurate and flexible technology for the manufacture of aircraft panels. Based on digitally adjustable multipoint tooling methodology, the technology is in the maturation process at DATAFORM, whose members are:

• The University of Cardiff (U.K.)

Jilin University (China)

Open Engineering S.A. (Belgium)

Cenaero (Belgium)

Kayser Italia (Italy)

Sener Ingeniería y Sistemas S.A. (Spain)

Multipoint forming (MPF) tooling already is being used in China to manufacture body panels of high-speed trains and construction column elements with irregular angles for Beijing’s national stadium (the Bird’s Nest), an architectural highlight of the Olympic Games. Jilin University has experience in MPF tooling methodology and is helping it become an established technology in the European aeronautical market. Within the DATAFORM project, the application possibilities of multipoint press forming, stretch forming, and jigless positioning processes are being explored while appropriate software is being developed to direct and control the manufacturing automatically.

Producing a panel with MPF technology is similar to the forming process with solid dies. Where the latter uses two opposite solid dies that are pressed on a sheet metal blank to conform it to a particular shape, MPF technology replaces the solid die with a matrix of several punches that are adjustable in height by means of linear actuators. This allows for fast changes in the kinds of shapes that can be produced from a particular unit.

While a solid die takes several months to be made, multipoint die forming, also known as discrete die, takes only several minutes for the die shape to be formed and set in position. Along with the time savings comes cost savings. A side benefit of discrete die is that it obviates the need for storage of solid dies.

Implementing software to drive adjustments of the discrete die creates the opportunity to build an automatic control system allowing for fast change of the punch array for whatever on-the-fly adjustments may be required.

As a first step in the process, the shape of the panel has to be defined by a CAD model. Then the design specifications must be introduced into the system, which will convert the data into the positioning of the punch array in the discrete die. Before setting all punch elements into position, possible deformation predictions of the panel can be calculated and taken into account when positioning the elements to obtain a more accurate result. Depending on the method used, an extra quality control can be introduced into the system by measuring the formed panel and repeating the process until all small forming defects have been eliminated. One study is focusing on how to automatically calculate and predict deformations in the beginning of the process. Studies on how to make the commercial CAD software compatible with the system are being undertaken.

To study all the different effects that can occur, finite-element modeling tools are being used to predict possible deformations. Defects including rupture, dimpling, wrinkling, and spring-back already have been examined in detail. For example, it has been found that dimpling, the golf-ball-like indentations caused by the rounded punches, can be avoided by use of an elastic interpolator that acts as a cushion to spread the force of the punches more equally across the surface of the blank.

Also being investigated are the usability and advantages of the technology for jigless positioning. The project involved construction of three prototypes—one each for multipoint press forming, multipoint stretch forming, and jigless positioning. Investigations will continue until October 2009.

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