TPT January 2007

It can consequently be expected that these three regions will exhibit the most resistance to a change in shape through hydroforming (bulge test). At these points one will thus also expect to find minima of the strain component in the circumferential direction. This is borne out by the bottom diagram in figure 18. Simulation of bulge test Figure 19 shows the experimental bulge test simulated by the finite element method. The simulation model of the tube generated in Copra ® FEA RF is used, with the material properties discussed above. The tube is continuously expanded radially by internal pressure.

depend, among other things, on suitable design of the geometry of the fin roll passes and the vertical positioning of the forming stands 4 . Finite element simulation can be used to predict the properties of roll-formed, longitudinally welded tubes and their suitability as semi- finishes for subsequent forming processes. This is of particular importance for the design of new tool sets and in the use of new kinds of high-strength material. The software package outlined here also presents a solution for analysing and optimising existent tool sets. A finite element model generated by Copra ® FEA RF can be used for further investigation within an extended process chain. For the case represented here, it was used for the welding process and bulge tests. 1. Karan Shah, Yingyot Aue-u-lan, Taylan Altan: ‘Using finite element analysis to roll-form tubes’ . Tube & Pipe Journal, October 2003. 2. BD Carleer: ‘FE Process Simulation for Tube Hydroforming, Starting with the Tube Forming Process’ . Proceedings from the International Conference on Hydroforming, sponsored by the University of Stuttgart, Germany, 6-7 November, 2001. 3. Michael Schäfer: Numerik im Maschinenbau. Springer Verlag, 1999. 4. Dirk Elsenheimer, Gerrit v. Breitenbach: ‘Untersuchung unterschiedlicher Rohreinformverfahren mit Optimierung für das Innenhochdruck-Umformen’ . Unpublished paper, Institute for Production Engineering and Forming Machines, Darmstadt University, 2004. 5. MSC.MARC 2003. Company Brochure MSC Software, Santa Ana, California, 2003. 6. Gerrit von Breitenbach, Ulrich Semmler: ‘Analyse unterschiedlicher Herstellverfahren längsnahtgeschweisster Rohre mit Optimierung für das Innenhochdruckumformen’ . Zwischenbericht zur Sitzung des EFB- Arbeitskreises ‘Übergreifende Optimierung in der Blechteilefertigung’ , 14 June, 2005, Dresden. 7. S Freitag, A Sedlmaier, G v Breitenbach: ‘Prediction of longitudinally welded tube and profile properties by using FE simulation’ . Proceedings of rollforming workshop at data M Software GmbH, Valley, Germany, 10-12 May, 2005. 8. Paul Scott: ‘The effects of frequency in high frequency welding’ . Transactions of Tube 2000, Toronto; ITA Publication. References

› Figure 19 : Simulation of tube bulge test with results matching practical experiment

The bulge test on the computer model matches the outcome expected from the practical experiment – the tube fails at about the 130° position.

Summary and outlook The Copra ® FEA RF computer program system enables the design and construction of roll tooling for the production of longitudinally welded, roll-formed tubes and profiles. Two special program modules allow simulation of the forming operation for its optimisation and validation. Using the finite element method, the forming of a tube is simulated and from this the theoretical wall thickness distribution and work hardening of the final tube are calculated. These values are compared to the results obtained by bulge tests. The accuracy of the simulation results is confirmed by the practical experiments. An essential finding of evaluation of the simulation is the correlation of the patterns of wall thickness and TEPS over the circumference. Increases in wall thickness result primarily from compression applied to the profile in a circumferential direction and longitudinal stress. Compression in a circumferential direction occurs – in this example – mainly when passing through fin passes. The longitudinal stress that contributes to a change in wall thickness is created by bending of the metal strip about the longitudinal axis. The quality of the treated tube and its hydroforming properties

data M Software – Germany Fax : +49 8024 640 300 Email : datam@datam.de Website : www.datam.de

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