P 355 - Development of a test method to determine the suitability of materials for hydroforming

The material properties that change over the circumference of the pipe as a result of the manufacturing process have not yet been considered, or only to a limited extent. For this reason, the material behaviour of tubes and sheets in relation to hydroforming was investigated in a joint project between the Institute for Production Technology and Forming Machines (PtU) at the Technical University of Darmstadt, the TNO Institute for Industrial Technology, Eindhoven (NL) and Engineering System International GmbH (ESI) Eschborn, in order to develop specific semi-finished product testing methods. The PtU concentrated its work on the semi-finished product tube, while TNO and ESI focussed on sheet metal testing using hydraulic cupping and thus the usability of an already known test method. In theoretical and practical investigations, the design features of hydroforming test rigs for pipes and sheet metal were developed and initial testing experience was gained with the aid of the test rigs realised on this basis. In the case of pipe testing, it was shown that both the pipe manufacturing process and various material parameters, especially geometry parameters, are of particular influence. The finite element simulation is in good agreement with the strains achieved in the real test results. This allows a good estimation of the time of failure. A comparison of the tube tests with the corresponding tests on sheet metal showed that some of the factors that determine the suitability for hydroforming could not be recognised in the case of sheet metal. The semi-finished product test for hydroforming properties of pipes must therefore always be carried out on the semi-finished pipe product. The test procedure developed for tubes enables tube manufacturers and hydroforming users to specifically analyse and test the semi-finished product properties that are of decisive importance for hydroforming. The test results make an important contribution to the optimisation of pipe production and to incoming inspection for hydroforming users. With regard to hydroforming plant operation, the measured forming pressures provide initial indications for process control and its adaptation. STUDIENGESELLSCHAFT STAHLANWENDUNG e.V.