Influence of the edge rounding process on the behaviour of blanked parts: numerical predictions with experimental correlation

Blanking of sheet metal is an important forming process in the automotive industry for the manufacture of mechanical components. The final component shape, obtained at the end of bending or deep-drawing processes, often has sharp edges due to the blanking operation. Concerning passenger safety components, like seat belt anchors, rounding of the edges by punching is necessary to avoid cutting the belt material. In addition to removing the sharp edges, the punching results in work hardening of the material in the rounded zones which results in an increase in the local resistance of the material. In this study, a high-strength low-alloy steel (HSLA S500MC) has been tested with the aim of quantifying the blanking and edge rounding operations. The mechanical behaviour of test specimens is investigated by means of tensile tests and the material is characterised in terms of Vickers micro-hardness. Numerical simulations of the edge rounding process are developed using previously identified material behaviour laws. The residual stress fields are characterised and compared to experimental results. This is done so that numerical simulation can be done in the future to prediction the in-service behaviour of the component. Specimens with rounded edges are compared to specimens that were not submitted to the rounding operation. It is shown that Edge Rounding by Punching improves the component resistance, therefore justifying the use of this process in the manufacture of automotive safety components.