Die-less forming of sheet metal parts

In a feasibility study, funded by the Stiftung Stahlanwendungs-forschung, Düsseldorf, the manufacturing of steel tubes for pipelines by forming with working media was examined. The idea for the manufacturing of tubes is based on the high-pressure forming of flat sheet metals. Flat sheets are congruently put one upon another and welded pressure-tight. A tubular structure arises from internal high-pressure forming with working media. With this process the manufacturing can be simplified in comparison with the production of seamless or welded tubes. This causes an improved stability for the tube. A further advantage arises if the forming process is carried out at the location where the tubes are used. In this way the transport volume is reduced considerably. The most essential process parameters are gage, geometry of blanks, welding method, working media and raw material. Fluids and gases are used as working media. Corrosion prevention, environmental compatibility and working safety must however be taken into account. Components of the examination were experiments in the model scale and FE-simulations. The examination stated that the tube production is possible by forming with working media. Already with a pressure of working media of approximately 0.5 MPa, a good expansion of the tube volume is carried out. Conventional and high strength steel is suitable for the process. The welding process (the size of welded joint and of the heat-affected zone) has a large influence on the expansion of the tube. The first FE-simulations produced an agreement of approximately 6% with the experiments. This shows that the number of required experiments can be reduced during further research by FE-simulations.