HAMMERING SHEET METAL INTO SHAPE

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HAMMERING SHEET METAL INTO SHAPE
27 February 2003 - Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.

The tool at the pressing plant resonantly pounds the sheet metal, ejecting the newly formed vehicle hood moments later. Although this operation runs like clockwork on the production line, it caused the developers of the metal-forming equipment many a headache, since sheet metal springs back (unbends elastically) when the press is opened.

The shaped part for a fender, for example, can differ from the forming tool by up to several centimeters. "To a large extent, the experts understand the mechanical behavior of sheet metal and modify the geometry of the tool accordingly," says Dr. Winfried Schmitt of the Fraunhofer Institute for Mechanics of Materials IWM. "Yet even they need several costly and time-consuming redesign cycles to achieve the required dimensional precision." The process becomes significantly more complex when forming thin sheets made of higher strength steel or light metals such as aluminum or magnesium alloys, since there is little experience of working with these modern materials. To shorten the route to the perfect shape, companies such as ThyssenKrupp, Müller-Weingarten and Karmann call on the knowledge, measurement techniques and calculations of experts at the Fraunhofer Competence Center for Component Simulation.

In the processing of sheet metal, especially in the case of complex shapes, there are many different forces at work: An area of the sheet that has been stretched may need to be compressed shortly afterwards. Other areas may be subject to different types of stress at slightly different times. Thin sheet metal, which is increasingly used in lightweight construction, is especially critical, since it is more prone to fracturing than conventional sheet metal. "It is precisely this varying temporal and spatial interplay of forces that was scarcely considered in previous simulation techniques," emphasizes Schmitt. "We therefore investigate the behavior of the sheet metal in combined tensile and compression tests. Once we have this reference data and the geometry of the pressing tool, the behavior of the entire component can then be reliably predicted by computer."

Similar problems occur elsewhere, in a completely different industry. The service life of electrical and electronic devices is often limited by the quality of the miniature plug-in connections. In this instance, the question is: What is the best way to form a copper connector, to allow for maximum elasticity and ensure reliable electrical contact? The computer model even allows designers to predict the gradual wear on metal surfaces through repeated connection cycles.

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The Fraunhofer-Gesellschaft undertakes applied research of direct utility to private and public enterprise and of wide benefit to society. Its services are solicited by customers and contractual partners in industry, the service sector and public administration. The Fraunhofer-Gesellschaft maintains over 80 research units at more than 40 different locations throughout Germany. A staff of some 12,700, predominantly qualified scientists and engineers, works with an annual research budget of over one billion euros. Of this sum, more than € 900 million is generated through contract research. Two thirds of the Fraunhofer-Gesellschaft’s contract research revenue is derived from contracts with industry and from publicly financed research projects. The remaining one third is contributed by the German federal and Länder governments, as a means of enabling the institutes to pursue more fundamental research in areas that are likely to become relevant to industry and society in five or ten years’ time.

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