Residual stresses in parts manufactured by near-net-shape-blanking

Near-net-shape-blanking processes enable to manufacture functional surfaces in a single manufacturing step, which offers great potential in the production of gears, for example. Among these processes are fineblanking, blanking with a small die clearance, blanking with a v-ring, precision blanking with and without a blank holder. All of these are able to produce almost identical cut-surfaces, this means a high proportion of clean-shear almost without a fracture zone, but plastic deformation in the shearing zone varies due to the different tool setups. Therefore, the residual stresses in the produced parts, which are highly relevant for the fatigue behavior of shear-cut gears, vary as well. These process-induced residual stresses are addressed in this paper. First, sheet metal strips made of S355MC (1.0976) were subjected to a stress relief heat treatment to get a defined and low initial residual stress state. Afterwards, a circular hole was cut in the strips by the five different blanking processes. The cut surfaces of the thus produced parts were measured as well as the hardness. The residual stresses in tangential and axial direction were measured for a depth of up to 0.34 mm by X-ray diffraction. Finally, a comparison between the different manufacturing techniques regarding the residual stresses is carried out.