Stretch flangeability of AHSS automotive grades versus cutting tool clearance, wear, angle and radial strain gradients

Abstract Stretch flangeability tests are performed on cold rolled AHSS automotive steel grades for crack sensitivity evaluation. The ISO16630 procedure is used with different cutting edge conditions including clearance, tool wear, angle and hole expansion punch geometry. Among all influence parameters, the clearance considered to be most critical control. Low (<10%) high (>20%) clearances significantly detrimental ratio (HER). An optimum in HER reached around 15% clearance. Both wear die each affect negatively values comparison new sharp tools. Varying concave convex punching geometries instead of orthogonal has a rather negative effect stretch due irregular cut quality along perimeter excessive configuration. geometry (flat R25, biaxial Nakajima R25 vs. 60° conical) also investigated. (true) proportional FE simulated logarithmic radial strain gradient at fracture.