Influence of pass reduction in cold rolling on damage evolution in deep drawing of rotationally symmetric cups

Abstract

Improvement of component performance by controlling the damage state after metal forming enables a reduction in sheet thickness and, consequently, in component weight and material cost. To establish methods for controlling damage in finished parts, the entire process chain from steelmaking and casting through hot and cold rolling to deep drawing must be considered. Previous research has shown that in hot rolling of an S355 steel, the influence of pass reduction on damage in the hot strip disappears when the accumulated pass reduction becomes large. However, the influence of cold rolling parameters on damage and specifically on its evolution in subsequent forming processes has not yet been systematically investigated. In the present work, specimens of the the mentioned S355 steel are cold rolled with two different pass reductions and heat treated to obtain a DP800 dual phase steel. These specimens are deep drawn into rotationally symmetric cups with variation of the drawing die radius. Sheet specimens and deep drawn cups are investigated using scanning electron microscopy to determine the respective void area fractions. While no influence of height reduction on the void area fraction after cold rolling is found, the void area fraction after deep drawing differs with variation of the pass reduction. This effect is connected to the formation of a larger number of small voids in the material rolled with a larger pass reduction.

Numerical Prediction of the Influence of Process Parameters and Process Set-Up on Damage Evolution during Deep Drawing of Rectangular Cups

“…This includes advantages inherent in the manufacturing process, such as strengthening of the material by work hardening. However, currently hardly any consideration is given to the damage occurring during the forming process and how it changes depending on the influencing factors along the process route [7]. Due to the complex nature of damage, which encompasses multiple scales and mechanisms, it is intrinsically difficult to predict and account for its evolution throughout the process route [6].…”

“…Moreover, depending on the process parameter and process set-up of each process step, a different damage state results. The damage state after deep drawing, however, is the one that influences the service properties of the component regarding fatigue and crash behavior [7]. In deep drawing, the sheet is first clamped between the blankholder and the die.…”