P 537 - Future potential of prefabricated blanks made of steel materials

P 530 - Extension of a semi-finished product test method for hydroforming Hydroforming (hydroforming) is used as a manufacturing process for hollow components in medium and large batch sizes. The semi-finished products used are usually longitudinally welded tubes. In the hydroforming process, the semi-finished tube is moulded into a tool engraving under the effect of the internal pressure of a liquid medium and the sliding movement of the axial punches. At the beginning of the forming process, the tube has no contact with the engraving; the forming process is determined by the balance between the forces applied and the reaction force of the tube. The hydroforming process is therefore particularly sensitive to changes in the semi-finished product properties. The pipe properties permitted by the relevant standards do not cover the requirements of hydroforming users. Testing the sheet materials does not provide sufficient information about the forming properties of the pipes, which are produced in a complex manufacturing process that is subject to a wide range of influencing factors. For this reason, a technological test method for tubes has already been developed (research project P 355 "Development of a test method to determine the suitability of materials for hydroforming"), which maps the stresses and strains that occur during hydroforming. The method has already been implemented in a commercially available test rig. It is not yet widely used to characterise hollow profiles. The semi-finished product testing method was therefore investigated in this research project with a view to standardisation. Standardised pipe characterisation enables IHU users to specify their requirements for the semi-finished product. The semi-finished product manufacturers are able to prove the suitability of their products for hydroforming. Various factors influencing the test method were determined in the research project. Test speed, test sequence control and the sensor technology used all have an influence on the test result. The influence of semi-finished product manufacture on the formability of the tubes in hydroforming was investigated by testing semi-finished products that had been moulded, longitudinally welded, heat-treated and, if necessary, calibrated using different methods. This showed that the most homogeneous possible semi-finished product properties over the circumference are a prerequisite for good utilisation of the forming capacity of the sheet materials used to manufacture the tubes. A uniform wall thickness is of particular importance here. A high-resolution measuring device was therefore developed to measure the wall thickness profile around the circumference of the tube. The proposals developed for a standardised semi-finished product test for hydroforming ensure comparability of the test results. forming ensure comparability of the test results obtained with different test equipment. This enables quantitatively definable requirements for the forming properties of the semi-finished product, which can be used to increase process reliability and thus improve the economic efficiency of hydroforming. Authors: P. Groche, G. von Breitenbach, R. Steinheimer Publication: 2004