Characterization and Utilization of Process-Induced Residual Stresses for the Manufacturing of Functional Surfaces by Near-Net-Shape-Blanking Processes

Near-Net-Shape Blanking processes are shear cutting processes that are able to manufacture parts with functional surfaces, that need no or only minimal post-processing. The functional surfaces are produced by plastic deformation, which can be used to control the residual stress state of the final component and thus its fatigue strength. The use of base materials with higher strength in combination with process-induced compressive residual stresses has considerable potential in terms of the targeted increase of the load carrying capacity with regard to the fatigue failure modes pitting and tooth root breakage. This offers the potential to replace cost- and time-intensive heat treatment in the manufacturing of power-transmitting gears by increasing the fatigue strength by locally adapted residual stresses. In the two-year follow-up project, this potential is to be investigated on a shear-cut pinion/wheel pair made from the previously used reference material and a higher strength steel. Fundamental relationships are systematically investigated with the models set up and validated by determining the tooth root bending strength in pulsator tests and the pit load carrying capacity in running tests.The residual stress states of the different gear variants are measured both before and after the fatigue tests. This allows to track process improvements but also ensures the predictability of the property improvements and the stability of the residual stresses. Thus, these measurements are used to extend the existing residual stress simulation model.By using a higher strength steel material, it will be shown that further improvements can be achieved in terms of tooth bending strength and pitting strength through process-induced residual stresses. Both experimental and numerical investigations are carried out for this purpose. In addition, the prediction of the respective load carrying capacity for the reference material and the higher strength material will be evaluated and if necessary improved. By integrating the results into the bidirectional model from the second funding period, it will be possible to design and manufacture shear cut gears of different materials and geometries with increased load carrying capacity by utilizing the positive effect of shear cutting process-induced residual stresses.The focus of the project is the design, layout and optimization of the NNSB processes with regard to an improved residual stress state for higher tooth bending strength and pitting strength, ensuring the predictability of the property improvements caused by residual stresses, and demonstrating residual stress stability in running tests under real operating conditions.

DFG Programme Priority Programmes

Subproject of SPP 2013:  The utilization of residual stresses induced by metal forming

Co-Investigators Dr.-Ing. Roland Golle; Dr.-Ing. Thomas Tobie