High-speed blanking and its potential for producing ultra-high-strength automotive safety components

¹ IUL - Institute of Forming Technology and Lightweight Components, Baroper Str. 303, 44227 Dortmund, Germany
² Autoliv B.V. & Co. KG, Emmy-Noether Str. 7a, 85221 Dachau, Germany
³ AS Norma, Laki 14, 10621 Tallinn, Estonia

^* Corresponding author: olaf.schrage@iul.tu-dortmund.de

Abstract

Ultra-High Strength Steel (UHSS) has the potential to replace high-carbon steel and eliminate the need for hardening heat treatment of parts, with both business and sustainability benefits. The high ultimate tensile strength (UTS) of UHSS currently limits its application in fine blanking and conventional shear cutting processes, used in the production of automotive safety parts. High-speed blanking (HSB), with punch speeds of approximately 4-7 m/s, overcomes this limitation. This is demonstrated here on martensitic steel (MS) with an UTS of 1500 MPa, and on C60 steel in cold-rolled condition with a UTS of 900 MPa. HSB experiments on 3 mm thick sheets using a hydraulic impact press produce straight blanked edges with low roll-over and burr, as well as smooth surface topography (arithmetic mean roughness < 1.5 µm). The width of the shear-affected zone at the cut edge is less than 50 µm due to induced localization. Automotive safety parts require high-edge ductility due to large deformations in crash scenarios. Hole tensile tests on both materials show that HSB edges match the ductility of wire-electrical-discharge-machined or milled edges. Furthermore, the edge ductility of the HSB of MS samples significantly surpasses that of C60 samples hardened to the same strength level.