Hot work tool steels (HWS) are widely used for high performance components as dies and molds in hot forging processes, where extreme process-related mechanical and thermal loads limit tool life. With the functionalizing and modification of tool surfaces with tailored surfaces, a promising approach is given to provide material flow control resulting in the efficient die filling of cavities while reducing the process forces. In terms of fatigue properties, the influence of surface modifications on surface integrity is insufficiently studied. Therefore, the potential of the machining processes of high-feed milling, micromilling and grinding with regard to the implications on the fatigue strength of components made of HWS (AISI H11) hardened to 50 ± 1 HRC was investigated. For this purpose, the machined surfaces were characterized in terms of surface topography and residual stress state to determine the surface integrity. In order to analyze the resulting fatigue behavior as a result of the machining processes, a rotating bending test was performed. The fracture surfaces were investigated using fractographic analysis to define the initiation area and to identify the source of failure. The investigations showed a significant influence of the machining-induced surface integrity and, in particular, the induced residual stress state on the fatigue properties of components made of HWS.

For the efficient manufacturing of thin-walled components in large quantities, multistage progressive die forming processes are suitable due to the automation potential and high output rates. This process approach is extensively used for fineblanking and stamping components. However, potential for lightweight design can be further realized by functional integration of these parts. Gearing geometries are common functional elements in this case. The bulk forming of these functional elements using sheet metal as semi-finished material can be attributed to sheet-bulk metal forming (SBMF). This process class is accompanied by challenges regarding the obtainable die filling. Furthermore, previous studies have shown that there is a geometry-dependent anisotropic material flow during the extrusion of functional elements from coil. Within this study, the forming stage of a multistage process setup, which consists of various trim operations and the forming stage, is investigated using a metal strip as coil layout geometry. As a workpiece, a circular component with an abstracted locking tooth geometry is manufactured by forward extrusion. By comparing the process results of the coil layout to the forming of a circular blank, the influence of the coil layout on the direction-dependent material flow is analyzed. In particular, the effect of the workpiece connector to the carrier strip on the resulting material flow is relevant within this study. Subsequently, strategies for the improvement of die filling by geometric adaption of the semi-finished material and varying the stage sequence are derived.