Stress Relief for Crack Prevention by Adding Holes to V-Bending Die

Press forming of metal sheets has been widely used in industry. Press forming processes clamp sheet-metal between upper and lower dies, and deform them into diversified shapes by plastic deformation [1]. V-bending is a representative method of the press forming process and is widely used in the metal working field because it enables the use of general-purpose dies to form products of various thicknesses and shapes [2]. However, the stress concentrates at the bottom of the V-groove, and it sometimes causes a crack to develop, which may result in die cracking. The cracking may occur due to fatigue in normal operation or incorrect operation which applies excessive load over specification. This study employed a special die geometry to suppress the cracking of the V-bending die. The special die geometry was obtained through three-step FEM analysis. First, topology optimization was conducted and suggested that two-holes might be effective for stress relief. Second, a parametric study by iterative s-FEM was used to find the position of the holes. Third, a further parametric study by FEM determined the detailed hole geometry. Finally, experiments verified the effect of the two-holes on stress relief.