Shear cutting of press hardened steel: influence of punch chamfer on process forces, tool stresses and sheared edge qualities

In order to cope with the difficulties of shearing operations of press hardened steels, this work attempted to optimize these processes. Herefore, it is necessary to reduce the press forces and stresses in tools, while still obtaining adequate sheared edge quality levels. To reach this goal, different punch chamfer angles (0°, 2°, 7° and 20°) and relative cutting clearances (5, 10 and 15 % of the sheet thickness) were tested in a cutting tool, which was adapted in a way that different active elements could be mounted. The tool was equipped with a measurement system, which allowed the determination of the process forces in three dimensions at each punch stroke. Basis was an AlSi coated 22MnB5 sheet with a thickness of 1.5 mm. In addition a finite element model was developed to predict the stress distribution in tools and the sheared edge qualities. According to the experimental results the application of a 20° chamfer angle succeeded to reduce the forces and stresses of tools, but the sheared parts had a poor quality. In contrast, the 7° chamfer angle gave lowest tool stresses and sufficient part qualities, but the forces were very high. The simulation results agreed with the experimental data, except for the prediction of the rollover zone. These deviations were attributed among others to the presence of the AlSi coating, which was not considered.