Tubular hydroforming of automotive side members with extruded aluminium profiles

Side member left and side member right, which go from bumper to bumper in a car body, were at the focus in the present study. These side members were produced using straight round (hollow with a circular cross-section) extruded aluminium profiles as tube material. The tubes were bent and hydroformed. Rotary-draw bending yielded the best result. A spread within 8 mm after bending was found to be acceptable provided that the bent tube was hydroformed with a high maximum internal pressure (1300 bar in this study). Pressure-assisted tool closure (hydroforming tool) should be preferred. Such a tool closure prevents formation of buckles, which may be difficult to straighten out completely during hydroforming. Planeness and parallelity of the press tables and adapters play a significant role, as far as the spread and inplaneness of hydroformed components are concerned. The hydroforming tool must be matched in the press that actually will be used. Proper evacuation (of particularly air) is essential, especially in long hydroforming tools. All cross-sections must be deformed at least 2% (average perimeter enlargement) if the hydroformed components are to exhibit a reasonable spread. The critical (fracture) cross-sections predicted by finite-element simulation corresponded to those found in practice. However, the finite-element simulation was not able to predict formation of wrinkles at the tube ends caused by excessively large strokes. Such wrinkles were obtained in practice.