Improving the springback behavior of deep drawn parts by macro-structured tools

Many automotive parts are manufactured by means of sheet metal forming technology. The process limits in sheet metal forming are highly dependent on the material flow and friction forces. In most cases, it is beneficial to reduce the friction between tool and workpiece to expand the process limits and increase the lifetime of tools. Macro structuring of tools is a novel approach to reduce the amount of friction forces in the deep drawing process [1]. The induced alternating bending in sheet metal during the deep drawing with macro-structured tools leads to an increase of its geometrical moment of inertia and consequently stabilizes the sheet against wrinkling. An increase in the peak-to-valley height difference, which is directly associated with a greater restraining force in flange area, leads directly to improved dimensional accuracy in terms of springback behavior of workpiece. This positive effect of the increased restraining force is known from the literature [2], but in lubricant free deep drawing process it is not applied by means of conventional blankholder force but also geometrically through macro structuring of tools. Within the scope of this paper, the influence of alternating bending on the springback behavior of parts in deep drawing process with macro-structured tools is studied. Since the springback in a workpiece depends on its material, two industry relevant materials DC04 and Al5182 are chosen for numerical and experimental tests. For this purpose conventional deep drawing process is compared with lubricant free deep drawing process. To investigate the effect of alternating bending on springback behavior of the components in lubricant free deep drawing with macro-structured tools, the ring splitting method is used. In this test, a ring from each cylindrical deep drawn cups formed by standard and macro-structured tools will be cut out and subsequently split to open. The opening gap of split ring indicate the amount of tangential residual stresses in rotationally symmetric deep drawing parts which is an indicator for springback behavior. The results of this paper show that springback behavior of sheet metal parts can be reduced by increasing the peak-to-valley height difference during lubricant free forming process with macro-structured tools.