Knockout punch

A European project aimed at making the production of aircraft body panels faster and cheaper is about to develop its first prototype.

After three years of research, a team of engineers and academics from around Europe are soon to unveil their first prototype for a new fast and flexible technology for producing aircraft panels.

The basic idea of the 'digitally-adjustable multipoint forming' tool is to replace a solid die (the metal block used to shape panels) with a matrix of several punches that are height adjustable using software. This would mean the punches could change to produce a variety of shapes within a short timescale.

The upshot of this, the researchers hope, will be that solid dies will no longer be necessary for panel making, leading to a significant reduction in costs and time.

The project, known as DATAFORM, started in 2006 with backing from the European Commission. Partners include institutions and companies from Europe and China, and it is being coordinated by the Manufacturing Engineering Centre at Cardiff University.

"This project focuses on forming metal panels, mainly aluminium ones, for the aeronautical industry," says Katy Vanbrabant of SENER, a Spanish engineering consultancy that is involved in the DATAFORM project.

"Even though the use of composites is increasing in the aeronautical industry, we believe that helping to reduce tooling costs and tool development time could help panel manufacturers supply aircraft panels faster and cheaper."

Multipoint forming (MPF) has already been used in China to produce body panels for highspeed trains, and the technique is also being used for the construction of columns with irregular angles for the national stadium for this summer's Olympic Games.

The researchers say that the contribution of China's Jilin University in MPF tooling methodology has been key to bringing the technology to the European aerospace industry.

The production of a panel by MPF technology is very similar to the forming process with solid dies. Where the latter uses two opposite solid dies that are pressed on a blank sheet metal to conform it to a particular shape, the MPF technology replaces the solid die with several punches.

While the solid die would take several months to be produced, however, the multi-point die forming, also known as discrete die, would take a matter of minutes to be set in position.

This would make it possible to start the forming process right after defining the shape of the 3D panel and then adjusting the discrete die into position.

The researchers also point out that the use of a discrete die can be a big space saver, as storage of the different specific form-dependent solid dies would no longer be necessary. At the same time, using software to drive adjustments of the discrete die creates the opportunity to build an automatic control system to obtain a more accurate panel, as the array of punches is able to rapidly change position to give the needed adjustments in the 3D panel if required.

Design led

The process to form the blank sheet metal into a panel according to aeronautical standards starts with design. As a first step, the shape of the panel has to be defined by a computer-aided design (CAD) model. Second, the design specifications need to be introduced into the system, which will convert the data into the positioning of the different punches of the discrete die.

Before setting all punch elements into position, possible deformation predictions of the panel can be calculated and taken into account to obtain a more accurate result. Depending on the method used, an extra quality control can be built into the system, by measuring the formed 3D panel and repeating the process until all defects have been removed.

Once the tool shape is set according to CAD data, a hydraulic press is used to shape the metal. After one pressing cycle, the formed shape is measured and can be re-formed with the tools if necessary - ensuring that 'spring-back' by the metal is compensated for.

Methods for making the commercial CAD software compatible with the system are being researched by the DATAFORM team to ensure that it can be easily transferable to meet industry needs.

There is also a continuing research project aimed at automatically calculating and predicting deformations early, which would make it possible to add corrections at the start of the forming process to avoid defects afterwards.

To study all the different effects that can occur, 'finite element method' tools are being used to predict possible deformations, the researchers say. In particular, defects like rupture, dimpling, wrinkling and springback have been examined in detail to obtain suitable solutions.

For example, dimpling, an effect caused by the different rounded punches that leave a golf-like surface on the panel, can be avoided by use of an elastic interpolator that acts as a cushion to spread the force of the punches more equally during the forming process. The use of elastic interpolator material to form the heads of the rounded punches can help to avoid this defect.

Universal tool

The researchers are also hopeful that their MPF technology will be able to be used in other engineering sectors as well as for manufacturing product prototypes.

DATAFORM is also investigating the usability and advantages of the technology for jigless positioning of panels.

"Right now the project is focused on the feasibility of the multipoint forming process in order to satisfy the aeronautical requirements," Vanbrabant says.

"Already some preliminary tests have shown satisfactory results, but much more work must be done from the CAD / CAE platform and the control system. This concerns both multipoint stretch forming and multipoint press forming technology. The multipoint positioning tooling technology, which can serve as a flexible fixture, should produce a first prototype later on this year."

She adds: "There is also the possibility of adapting the multipoint forming technology to composite manufacturing, but that would only be possible when starting a new research project specifically on this subject.

"On the other hand, this technology could be also suitable for other industrial fields, where the need exists for manufacturing medium-sized panels of medium series with a process lying between bending and stamping."

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