This paper deals with different aspects of the hydroforming technology and its relevance for the automotive industry. Starting from a brief description of tube hydroforming and sheet hydroforming, the paper shows the progressive developments of both technologies, using results of R&D projects, prototypes and serial production parts as examples. Considerations on the future trends and chances of the hydroforming technologies will close the paper.

Tribological aspects strongly influence the deep drawing behaviour of sheet metal, being responsible for both the punch force and the material draw-in from the flange. Recent developments in lubrication technology have shown that dry film lubricants can be a good alternative to conventional fluid lubricants in case of aluminium sheets. Their main advantages are the homogeneous distribution on the blank surface, the good adhesion to the surface and the possibility of applying it already in the rolling mill. In order to introduce this technology in series production also for steel sheets more knowledge concerning the influence of the lubricant amount on the drawing forces is needed. A further important aspect to be considered is the surface quality of the steel grades and its interactions with the dry lubricant. In this paper four steel grades with different mechanical and/or surface properties are considered. After a microscopical and topographical investigation of the surface the materials were tested in a cup drawing test after applying two different amounts of the dry film lubricant Drylube E1. Further process parameters which were varied are the blank holder force FN and the drawing ration b. In this way, information about the influence of the lubricant amount on both the drawing force and on the maximum blank holder force FZ could be obtained for three different values of b. The experimental results have shown how a strong decrease of the lubricant amount (from 1.0 down to 0.5 g/m2) causes, at a given drawing ratio, only a small increase in the maximum drawing force as well as a small increase in the maximum blank holder force.

Tailored welded blanks are already used in the series production of deep drawn parts, and are now considered also for other forming technologies, like for example hydroforming. As new materials come into the market, also their combinations in the production of new tailored welded blanks increase, improving on the one hand the possibilities of matching material and functional requirements, but making the material characterisation more difficult on the other hand. For this reason new methods for a fast, precise and flexible characterisation of the mechanical and tribological properties of tailored welded blanks are needed. In particular the FE‐analysis, a powerful instrument for the definition and optimisation of forming processes, needs precise and reproducible material data in order to deliver accurate results. Therefore, when working with tailored welded blanks, it is crucial that the weld line is modelled using mechanical and tribological properties which refer to its structure and surface. This work summarises the methods used for the characterisation of the mechanical properties of the weld line at the chair of manufacturing technology in Erlangen and presents the results obtained for four different steel grades (FeP04, ZStE340, DP450 and TRIP800) and the tailored welded blanks obtained by their combinations. The accuracy of the results obtained in tensile and in friction tests were verified in simple experiments by comparing results from the tests with results from the finite element analysis. These were seen to be in very good accordance, confirming the accuracy of methods used in the material characterisation.

This paper presents a method for the experimental determination of forming limit diagrams under non linear strain paths. The method consists in pre-forming the sheets under two different strain conditions: uniaxial and biaxial, and then stretching the samples, cut out of the preformed sheets, using a Nakajima testing setup. The optical deformation measurement system used for the process analysis (ARAMIS, Company GOM) allows to record and to analyze the strain distribution very precisely with respect to both time and space. As a reference also the FLDs of the investigated grades (the deep drawing steel DC04, the dual phase steel DP450 and the aluminum alloy AA5754) in as-received conditions were determined. The results show as expected an influence of the pre-forming conditions on the forming limit of the materials, with an increased formability in the case of biaxial stretching after uniaxial pre-forming and a reduced formability for uniaxial load after biaxial stretching if compared to the case of linear strain paths. These effects can be observed for all the investigated materials and can be also described in terms of a shifting of the FLD, which is related to the art and magnitude of the pre-deformation.

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