Experimental and numerical investigation of ironing in deep drawn parts

Majority of the industrially relevant deep drawn sheet metal parts undergoes an additional process after the drawing operations. Operations like flanging or hole extrusion are widely used especially in the automotive industry. In such industrial applications it is seen that process planers design the tools by using a clearance less than the sheet thickness. Due to this smaller gap between the forming steels and the post, sheet material is compressed in the thickness direction. This additional compression is definitely needed for collar forming and it is beneficial in flanging operations in terms of springback. Addition of compressive deformation state on flange regions reduces the bending effects on those parts. Ironing in sheet thickness direction is a challenging deformation state for numerical simulations. This effect can be modelled by 3D continuum elements. However, due to high computation times this solution is not feasible for industrial applications. On the other hand, shell elements are widely used in sheet metal forming problems due to their efficiency but the conventional shell elements cannot predict ironing effects since the formulation does not consider through-thickness deformation. In order to analyze the effect of ironing, cup drawing experiments were performed. Ironing level is controlled by changing the die diameter while keeping the punch diameter constant. DC04-SUPERMOD with 1.75 mm thickness was used in the experiments. The thickness distribution along the cup wall and height of the cups were measured after each operation. Same experimental procedure was modeled using new thick shell elements which accounts for the through-thickness deformation. Comparison with the experimental measurements show that the enhanced formulation of the shell elements can be used to simulate the ironing effects in deep drawn parts.