Chassis for e-mobility: Bainitic steels and hydroforming reduce weight and increase operational stability
05.06.2019 | Initiative Automotive
Current electric battery operated or hybrid drive vehicles are heavier due to their onboard energy storage systems and partial component duplication in the powertrain. This is what frequently increases the vehicle's overall weight. The need to adapt the structure of the bodywork and chassis to guard against typical load cases resulting from driving and crash scenarios results in greater weight in most instances.
A particular challenge is posed by the need to safeguard the operational stability of chassis frame structures, often known as subframes or integral subframes, having due regard to the package restrictions which are even narrower than with conventional drive concepts.
Today, hydroforming is already the method generally used to shape axle frames to meet their stress specifications and the manufacturing method, materials and wall thicknesses are carefully matched to each other. Consequently, experts regard the technical quality of hydroformed axles as being particularly high - they are also commercially attractive due to their fully interlinked production concepts.
Compared with alternative materials, the hot-rolled bainitic top products from Salzgitter Flachstahl GmbH not only exhibit a higher degree of stability with static characteristics but also display considerable performance gains, particularly with regard to the dynamic stresses in welded constructions.
The initial trial results from Salzgitter Mannesmann Forschung GmbH led to the selection of SZBS600 as the material for further intensive study for use as the particularly robust axle frames required for electromobility.
Under the 'Initiative Automotive' by Salzgitter AG, the companies are working together on implementing this. The SZBS600 from Salzgitter Flachstahl GmbH was tubed and the hydroforming component was produced in conditions close to mass production at Salzgitter Hydroforming GmbH. At Salzgitter Mannesmann Forschung GmbH, a comparison was made between the two hydroforming components - one in SZBS600 and one in S460MC, a typical reference material.
Results: The challenging reforming, with a higher degree of stability, was absolutely comparable with the less stable S460 MC. The maximum circumferential expansion figures obtained in the burst test of 13.4% with the SZBS600 compared with 11.3% (S460MC) were perceptibly higher, and this was even with a 0.2 mm reduction in wall thickness.
And the best of all: Both the material SZBS600 and hydroforming as the manufacturing process are immediately available at Salzgitter and can be used without reservation to increase operational stability and/or reduce weight in components used in e-mobility.