Effect of shearing clearance and angle on stretch-flange formability evaluated by saddle-type forming test

• The optimum shearing clearance and angle for stretch-flange formability was derived.
• The saddle-type forming test was adopted for evaluation of stretch-flange formability.
• The fracture ratio on sheared surface becomes high at the optimum shearing conditions for stretch-flange formability.
• Compression stress becomes low at the specific shearing angle to induce high fracture ratio.

In this study, the effects of shearing clearance and shearing angle on stretch-flange formability are investigated. The saddle-type forming test is adopted for this investigation. A notch-type shearing line, which comprises straight and circular arcs, is used for this test. The results show that stretch-flange formability is improved in narrow clearances. This tendency is different from that obtained by the hole expansion test, wherein stretch-flange formability is improved in large clearances. This improvement might be caused by the increase in the area of the fractured surface in narrow clearances. Generally, the larger the fractured surface, the smaller the work hardening on a sheared edge. Furthermore, the investigation reveals the existence of an optimum shearing angle for excellent stretch-flange formability. FE simulation shows that the optimum shearing angle increases hydrostatic stress in materials during shearing. Compressive stress across the material thickness is mainly affected by shearing angle. The result of the analysis suggests that the optimum shearing angle increases the area of the fractured surface to improve stretch-flange formability.