Enhancing edge integrity of high-strength steels by high-speed blanking to achieve improved crashworthiness

Abstract

The increasing use of ultra-high-strength steels (UHSS) in automotive safety components is driven by stricter crash safety requirements, vehicle weight reduction, and ecological goals in production and service. The application of UHSS requires adaptations in the manufacturing process chain, as conventional slow-speed blanking (SSB) used in mass production is challenging due to tool wear. Another aspect is crashworthiness: The interaction between material properties and blanking-induced defects—such as surface irregularities, microvoids, and microcracks—promotes crack initiation at free edges and limits edge formability. Local plastic deformation without breakage is a precondition for a stable break load of safety components, wherefore edge stretchability serves as an indicator for crashworthiness. High-speed blanking (HSB) of three steels with ultimate tensile strengths in the range of 1500 MPa—martensitic Docol 1500M, press-hardened (PH) 22MnB5, and carbon steel C60—is examined. Blanking trials are followed by central-hole tensile tests (CHTT) to assess edge stretchability. HSB produces edges with high geometric accuracy and homogeneous fracture surfaces, exhibiting roughness values comparable to wire-eroded surfaces. The shear-affected zone is confined to a narrow band of less than 2% of the sheet thickness, which is four times smaller than those observed in SSB. CHTT results show that HSB edges retain the same load-bearing capacity and edge fracture strain as wire-eroded edges, showing that edge integrity has not been compromised by HSB. In contrast, SSB triggers premature crack initiation reducing the achievable fracture strain by nearly half.